Coarse Sand Layer Research Articles

Denitrification potential in relation to lithology in five headwater riparian zones.

The influence of riparian zone lithology on nitrate dynamics is poorly understood. We investigated vertical variations in potential denitrification activity in relation to the lithology and stratigraphy of five headwater riparian zones on glacial till and outwash landscapes in southern Ontario, Canada. Conductive coarse sand and gravel layers occurred in four of the five riparian areas. These layers were thin and did not extend to the field-riparian perimeter in some riparian zones, which limited their role as conduits for ground water flow. We found widespread organic-rich layers at depths ranging from 40 to 300 cm that resulted from natural floodplain processes and the burial of surface soils by rapid valley-bottom sedimentation after European settlement. The organic matter content of these layers varied considerably from 2 to 5% (relic channel deposit) to 5 to 21% (buried soils) and 30 to 62% (buried peat). Denitrification potential (DNP) was measured by the acetylene block method in sediment slurries amended with nitrate. The highest DNP rates were usually found in the top 0- to 15-cm surface soil layer in all riparian zones. However, a steep decline in DNP with depth was often absent and high DNP activity occurred in the deep organic-rich layers. Water table variations in 2000-2002 indicated that ground water only interacted frequently with riparian surface soils between late March and May, whereas subsurface organic layers that sustain considerable DNP were below the water table for most of the year. These results suggest that riparian zones with organic deposits at depth may effectively remove nitrate from ground water even when the water table does not interact with organic-rich surface soil horizons.

Infiltration and redistribution of LNAPL into unsaturated layered porous media

Enhanced understanding of light non-aqueous phase liquid (LNAPL) infiltration into heterogeneous porous media is important for the effective design of remediation strategies. We used a 2-D experimental facility that allows for visual observation of LNAPL contours in order to study LNAPL redistribution in a layered porous medium. The layers are situated in the unsaturated zone near the watertable and they are inclined to be able to observe the effect of discontinuities in capillary forces and relative permeabilities. Two experiments were performed. The first experiment consisted of LNAPL infiltration into a fine sand matrix with a coarse sand layer, and the second experiment consisted of a coarse sand matrix and a fine sand layer. The numerical multi-phase flow model STOMP was validated with regard to the experimental results. This model is able to adequately reproduce the experimental LNAPL contours. Numerical sensitivity analysis was also performed. The capillarity contrast between sands was found to be the main controlling factor determining the final LNAPL distribution.

Hydrodynamic characteristics of the western Do�ana Region (area of El Abalario), Huelva, Spain

The Donana region, in southwestern Spain, comprises a large and important nature reserve, the wetlands of which are affected by human activity. Planting of an extensive eucalyptus forest in the 1950s and, more recently, the use of aquifers for irrigation and water supply for some coastal tourist resorts, have altered the natural groundwater-flow system. The area of the study is the western sector of the region, called El Abalario, which is a gentle topographic elevation between the Atlantic coast and La Rocina Creek (Arroyo de la Rocina). Underneath a variable layer of eolian sands with high dunes near the coast, thick Plio-Quaternary detritic strata, mostly fine silica sands, overlie marls. Near the base there is a variable, deltaic-origin layer of coarse sands and gravels. The dome-shaped water table, inside the sands, is close to the surface everywhere except beneath the dune belt, and small, temporary, shallow lagoons are numerous. The coarse sand and gravel layer conditions groundwater flow and behaves as a semiconfined layer between sands. A cross section through the area was simulated with a model to check the validity of the conceptual groundwater-flow pattern and its sensitivity to the hydraulic parameters. The model was calibrated using parameter values obtained by pumping tests and multilevel piezometric data, and checked against the estimated groundwater discharge into La Rocina Creek. Groundwater flows peripherally to the sea coast, to La Rocina Creek, or directly east and southeastward into the Donana marshlands, in the Guadalquivir River delta. The average net aquifer recharge rate was calculated to be between 100 and 200 mm year−1 for the area covered by brush, but is remarkably lower in the areas of eucalyptus trees. The transient-state model shows that recharge varies spatially and is not clearly proportional to annual precipitation. Phreatic evapotranspiration plays an important role in decreasing the net value of aquifer recharge to approximately 0.4–0.6 of that calculated with a soil-balance model. The cross section model was used to study the effect of groundwater abstraction on water-table depth by subtracting the contribution of vertical flow, calculated by a well-hydraulics formula, to the semiconfined deep aquifer. The result was a decrease in phreatic evapotranspiration, flow into La Rocina Creek, and lagoon-inundation frequency. Replacement of the eucalyptus forest with native vegetation may raise water-table levels and even reactivate old tributaries to La Rocina Creek.

Depositional history and evolution of the Paso del Indio site, Vega Baja, Puerto Rico

AbstractPotshards discovered during excavation of bridge pilasters for a major expressway over the Rio Indio floodplain, a stream incised within the karsts of north‐central Puerto Rico, required large‐scale archaeological excavation. Five‐meter‐deep bridge pilaster excavations in the alluvial valley provide a 4500‐year history of deposition. Stratigraphic analysis of the exposed pilaster walls in combination with textural and organic carbon analyses of sediment cores obtained over a much broader area suggest a fluvial system dominated by overbank deposition. Six sequences of alternating light and dark layers of sediment were identified. The darker layers are largely composed of silts and clays, whereas the lighter layers are rich in sand‐sized sediment. Archaeological evidence indicates the organic‐rich dark layers, believed to be buried A horizons, coincide with pre‐historic occupation by Cedrosan Saladoid, Elenan Ostionoid, and Chican Ostionoid, extending from A.D. 450 to A.D. 1500. Lighter layers below the dark soil horizons are interpreted as overbank deposits from large magnitude flood events. The floodplain aggraded discontinuously with rapid deposition of sand followed by gradual accumulation of silt, clay, and organic material. An approximately 1‐m‐thick layer of coarse sand and gravel halfway up the stratigraphic column represents an episode of more frequent and severe floods. Based on radiocarbon ages, this layer aggraded between A.D. 1000 and A.D. 1100, which is well within the Elenan Ostionoid era (A.D. 900–1200). Rates of sedimentation during this period were approximately 8 mm per year, ten times greater than the estimates of sedimentation rates before and after this flood sequence. The cause for the change in deposition is unknown. Nonetheless the Elenan Ostionoid would have had to endure frequent loss of habitation structures and crops during these events. © 2003 Wiley Periodicals, Inc.

Temporal development of prograding beach–shoreface deposits: the Holocene of Kujukuri coastal plain, eastern Japan

Prograding beach–foreshore deposits with a basal ravinement bed are recognized from detailed AMS 14C dating and grain size analyses of Holocene deposits of the Kujukuri coastal plain facing the Pacific coast of Japan. The Holocene deposits are about 20 m thick and consist of an upward-shoaling beach–foreshore succession that has a basal unconformity overlain by a thin layer of relatively coarse sand. The unconformity is a downlap surface, which originated from a ravinement surface. The overall succession was formed by a prograding beach–foreshore system during the highstand in sea level of the last 6000 years. Poorly preserved fossil shells, enclosed in the thin layer of coarse sand at the base of the succession, date from the transgressive stage in sea level before 6000 cal yr BP. Grain size distribution patterns are polymodal in the basal sand layer and unimodal in the remainder of the succession. Modal classes of the basal part are fine (3.3–2.6φ), medium (2.3–1.8φ), and coarse (1.2–1.0φ). The fine mode and the unimodal grain sizes define an overall upward-coarsening trend, which correlates with the upward-shoaling succession. In contrast, the medium and coarse modes are restricted to the basal sand, and are interpreted as related to the ravinement process. The thin basal sand layer, an admixture of these modal classes, is interpreted as a type of ravinement deposit preserved during sea-level highstand. No transgressive deposit was preserved on the ravinement surface because sediment supply was so small that the sediment on this surface experienced thorough reworking by storm waves.

Biomass accumulation and carbon utilization in layered sand filter biofilm systems receiving milk fat and detergent mixtures

This research evaluated utilization of organic compounds and biomass accumulation in three different layered sand filter biofilm systems renovating a mixture of detergent and milk fat. Organic compounds were measured as chemical oxygen demand (COD) and biomass as ATP. A two-layer sand filter with coarse sand on the top and fine sand at the bottom; a three-layer sand filter with pea gravel on the top, coarse sand in the middle, and fine sand at the bottom; and a two-filters in-series sand filter biofilm system each received mixtures of butterfat and detergent. While the three-layer sand filter system had greater COD utilization capacity due to a longer filter run, the two-filters in-series sand filter system had greater COD utilization efficiency. The COD utilization was highly associated with the period of filter run to clogging. The decrease of COD utilization rate could lead to the clogging of sand filters. To maintain long filter runs without clogging, a COD loading rate of 2100 mg O 2/m 2/h was recommended for three-layer sand filters and 1800 mg O 2/m 2/h for two-layer sand filters for high fat content wastewater. In the two-layer sand filters and the three-layer sand filters, biomass did not seem to accumulate in any particular layer on a unit volume of sand. However, based on unit surface area, the coarse sand layer accumulated more biomass than the fine sand layer and the pea gravel layer.

Investigações geofísicas na borda da bacia sedimentar de São Paulo

Este artigo mostra resultados parciais de investigações geofísicas realizadas na borda da Bacia Sedimentar de São Paulo, dentro do campus da Universidade de São Paulo. O principal objetivo desta pesquisa é a caracterização dos sedimentos e do topo das rochas do embasamento da bacia, utilizando os métodos GPR-Ground Penetrating Radar e Resistividade Elétrica. Os perfis geofísicos foram realizados ao longo de uma mesma linha, visando comparar os resultados com as duas metodologias. Um perfil de 216m foi adquirido com as antenas de 50 MHz e um perfil de resistividade com dipólos de 20m. Além disso, duas Sondagens Elétricas Verticais - SEV's foram feitas sobre a mesma linha. A análise do perfil GPR permitiu identificar o limite entre a base do solo e uma camada de areia. Os resultados estão de acordo com as informações de poços. O perfil elétrico identificou uma zona anômala de condutividade entre 80 e 110 m, relacionada provavelmente com uma zona de cizalhamento.

Palynology and paleoecology of strata associated with the Ohoopee river dune field, Emanuel county, Georgia

Fourteen auger holes were drilled through ancient dunes near the Ohoopee River in Emanuel County, Georgia. Driller's logs and sieve analyses show that the wind‐blown sands of the dune field overlie a layer of coarse sand and gravel, which in turn overlies clayey Late Tertiary strata. Clay‐rich sediment recovered from two of the holes contained diatoms, sponge spicules, and other siliceous marine microfossils, while clay analyses from seven other holes revealed the presence of the clay mineral attapulgite (a variety of palygorskite). Twenty‐two sediment samples collected from six of the drill holes contained sufficient organic material to warrant palynological analysis. Eighty‐one taxa of pollen, spores, and algal cysts were used along with the diatoms, clay analyses, and stratigraphy to indicate probable ages and environments of deposition of the sediments. Both the diatoms and the attapulgite indicate marine depositional conditions. Overlying the marine units, but below the eolian sands we found rare occurrences of the extinct or extirpated genera Casuarinidites, Sciadopitys, Pterocarya, and Momipites. We believe these support a Late Tertiary age interpretation for the clayey strata. The presence of taxa such as the Cyrillaceae, Nyssa, Sphagnum, Myriophyllum, and Pseudoschizaea in the uppermost Tertiary units indicates that these sediments accumulated in freshwater wetlands. Our interpretation of the depositional history is that Late Tertiary marine strata accumulated first, probably during the Miocene. As sea level dropped fluvial and paludal conditions led to the accumulation of freshwater swamp/marsh sediments and probable stream sands or gravels later in the Tertiary. Exposure of the Inner Coastal Plain during the Pleistocene resulted in the formation of dunes that migrated over the Tertiary strata at the site of deposition.

Lacustrine Sedimentary Environments in High Arctic Proglacial Bear Lake, Devon Island, Nunavut, Canada

Combined catchment, subbottom acoustic, and sedimentary studies of high arctic, proglacial Bear Lake, Devon Island, were carried out to evaluate the role lacustrine processes and Holocene catchment evolution have had on the sedimentary record. In the proximal basin, bottom deposits up to 60 m thick are generated in part by turbid underflows associated with peak meltwater flow from the Devon Island Ice Cap. These underflows produce rhythmically laminated structures that are likely varves. In shallower locations, accumulation is slower and results from homopycnal distribution of fine suspended sediment throughout the proximal basin, resulting in a simple varve couplet. The distal basin is isolated from glacial meltwater by a shallow sill, although some fine-grained detrital carbonate transported by the glacial meltwater is deposited in both basins. In most locations in the distal basin Holocene sediments are less than 10 m thick. They are composed primarily of massive clay and some carbonate interrupted by irregular graded carbonate units produced by sporadic heavy summer rainfall and sediment transport from small plateau tributaries. Eolian sedimentation is also important throughout the lake, especially when high accumulations melt through the ice in the proximal basin, producing isolated grains and layers of coarse sand in the sedimentary record. Holocene ice margin changes have influenced the sedimentary record substantially, particularly during the mid-Holocene when the ice cap is inferred to have retreated from the catchment.

Lacustrine Sedimentary Environments in High Arctic Proglacial Bear Lake, Devon Island, Nunavut, Canada

Combined catchment, subbottom acoustic, and sedimentary studies of high arctic, proglacial Bear Lake, Devon Island, were carried out to evaluate the role lacustrine processes and Holocene catchment evolution have had on the sedimentary record. In the proximal basin, bottom deposits up to 60 m thick are generated in part by turbid underflows associated with peak meltwater flow from the Devon Island Ice Cap. These underflows produce rhythmically laminated structures that are likely varves. In shallower locations, accumulation is slower and results from homopycnal distribution of fine suspended sediment throughout the proximal basin, resulting in a simple varve couplet. The distal basin is isolated from glacial meltwater by a shallow sill, although some fine-grained detrital carbonate transported by the glacial meltwater is deposited in both basins. In most locations in the distal basin Holocene sediments are less than 10 m thick. They are composed primarily of massive clay and some carbonate interrupted by irregular graded carbonate units produced by sporadic heavy summer rainfall and sediment transport from small plateau tributaries. Eolian sedimentation is also important throughout the lake, especially when high accumulations melt through the ice in the proximal basin, producing isolated grains and layers of coarse sand in the sedimentary record. Holocene ice margin changes have influenced the sedimentary record substantially, particularly during the mid-Holocene when the ice cap is inferred to have retreated from the catchment.

PALYNOLOGY AND PALEOECOLOGY OF STRATA ASSOCIATED WITH THE OHOOPEE RIVER DUNE FIELD, EMANUEL COUNTY, GEORGIA

Abstract Fourteen auger holes were drilled through ancient dunes near the Ohoopee River in Emanuel County, Georgia. Driller's logs and sieve analyses show that the wind‐blown sands of the dune field overlie a layer of coarse sand and gravel, which in turn overlies clayey Late Tertiary strata. Clay‐rich sediment recovered from two of the holes contained diatoms, sponge spicules, and other siliceous marine microfossils, while clay analyses from seven other holes revealed the presence of the clay mineral attapulgite (a variety of palygorskite). Twenty‐two sediment samples collected from six of the drill holes contained sufficient organic material to warrant palynological analysis. Eighty‐one taxa of pollen, spores, and algal cysts were used along with the diatoms, clay analyses, and stratigraphy to indicate probable ages and environments of deposition of the sediments. Both the diatoms and the attapulgite indicate marine depositional conditions. Overlying the marine units, but below the eolian sands we found...

Distribution of Methanotrophs in Trichloroethylene-Contaminated Aquifers in a Natural Gas Field

The distribution of methanotrophs was examined in shallow aquifers contaminated with trichloroethylene in the southern Kanto gas field, Chiba, Japan. The total populations of methanotrophs and the numbers of methanotrophs producing soluble methane monooxygenase (sMMO) were determined separately. Hydrostratigraphic units of a Pleistocene to Holocene stratum consisted of three aquifers separated by nontransmissive silt layers. Dissolved methane concentrations increased with depth and were highest in the third aquifer. The number of methanotrophs was higher in the second aquifer than in the first aquifer. A clear relationship was observed between microbial populations and lithofacies. The greatest abundance of methanotrophs was observed in the coarse sand layers of the second aquifer, with the lowest abundance observed in silt layers. The high abundance of methanotrophs in the coarse sand in the second aquifer implied that this part of the stratum plays an important role in in situ bioremediation.

FUSSIM2: brief description of the simulation model and application to fertigation scenarios

Standard theories for water movement, solute transport and uptake by roots can be applied to closed, recirculating cropping systems, even when coarse substrates are used. Some of these systems, such as bedding systems or potting plants, are vulnerable to accumulation of solutes in the root zone, which may be harmful to crop development. A two-dimensional simulation model for the above-mentioned processes is briefly described. This model can be used, amongst other possibilities, to search for good fertigation strategies in order to minimise solute accumulation in the root zone. This modelling approach can largely reduce the number of experiments. Some simulated scenarios showing different distributions of the electrical conductivity in a layer of 15-cm coarse sand are presented. This study is not meant to be an extensive search for the best fertigation strategy but to demonstrate how the simulation model can help in finding alternative strategies.

Legacy of the California Gold Rush: Environmental Geochemistry of Arsenic in the Southern Mother Lode Gold District

Gold mining activity in the Sierra Nevada foothills, both recently and during the California Gold Rush, has exposed arsenic-rich pyritic rocks to weathering and erosion. This study describes arsenic concentration and speciation in three hydrogeologic settings in the southern Mother Lode Gold District: mineralized outcrops and mine waste rock (overburden); mill tailings submerged in a water reservoir; and lake waters in this monomictic reservoir and in a monomictic lake developing within a recent open-pit mine. These environments are characterized by distinct modes of rock-water interaction that influence the local transport and fate of arsenic. Arsenic in outcrops and waste rock occurs in arsenian pyrite containing an average of 2 wt% arsenic. Arsenic is concentrated up to 1300 ppm in fine-grained, friable, iron-rich weathering products of the arsenian pyrite (goethite, jarosite, copiapite), which develop as efflorescences and crusts on weathering outcrops. Arsenic is sorbed as a bidentate complex on goethite, and substitutes for sulfate in jarosite. Submerged mill tailings obtained by gravity core at Don Pedro Reservoir contain arsenic up to 300 ppm in coarse sand layers. Overlying surface muds have less arsenic in the solid fraction but higher concentrations in porewaters (up to 500 μg/L) than the sands. Fine quartz tailings also contain up to 3.5 ppm mercury related to the ore processing. The pH values in sediment porewaters range from 3.7 in buried gypsum-bearing sands and tailings to 7 in the overlying lake sediments. Reservoir waters immediately above the cores contain up to 3.5 μg/L arsenic; lake waters away from the submerged tailings typically contain less than 1 μg/L arsenic. Dewatering during excavation of the Harvard open-pit mine produced a hydrologic cone of depression that has been recovering toward the pre-mining groundwater configuration since mining ended in 1994. Aqueous arsenic concentrations in the 80 m deep pit lake are up to 1000 μg/L. Redistribution of the arsenic occurs during summer stratification, with highest concentrations at middle depths. The total mass of arsenic in the pit lake increases coinciding with early winter rains that erode, partially dissolve, and transport arsenic-bearing salts into the pit lake. Arsenic concentration, speciation, and distribution in the Sierra Nevada foothills depend on many factors, including the lithologic sources of arsenic, climatic influences on weathering of host minerals, and geochemical characteristics of waters with which source and secondary minerals react. Oxidation of arsenian pyrite to goethite, jarosite, and copiapite causes temporary attenuation of arsenic during summer, when these secondary minerals accumulate; subsequent rapid dissemination of arsenic into the aqueous environment is caused by annual winter storms. As the population of the Mother Lode area grows, it is increasingly important to consider these effects during planning and development of land and groundwater resources.

Funneled flow mechanisms in a sloping layered soil: Laboratory investigation

Artificial capillary barriers are being used to divert water away from sensitive underground regions. Conversely, funneled flow over natural capillary barriers may increase the danger of groundwater contamination by decreasing the travel time and contact area. There have been relatively few experimental studies of capillary barrier flow patterns. In this study, water was applied uniformly across the top surface of a backlit tilting chamber, 1 cm thick, 110 cm high, and 180 cm long, in which a coarse sand layer was imbedded in a fine sand. Bedding slope and water application rates were varied between 0° and 12° and 1 and 3 cm h−1, respectively. After attaining steady state, matric potential was measured along the textural interface, and photos of dye traces were taken in order to visualize streamlines. The funneled flow was characterized by three discrete regions: an initial capillary diversion, a breakthrough region, and a toe diversion. The breakthrough region consisted of a significant zone of partial breakthrough where the vertical flux into the coarse layer was less than the water application rate. The lateral distance of the capillary diversion was explained well by previously published relationships when the water entry value at the textural interface was replaced by lower, observed matric potential at which breakthrough occurred at the most upslope point. The length of the capillary diversion was overpredicted using the air entry value. Finally, the toe of the coarse layer had significant, observed effects on funneled flow patterns, which have previously received little, if any, attention. The results of this study imply that the slope of the coarse layer and infiltration rate will largely govern the effectiveness of capillary barriers and that capillary barriers are less effective than previously assumed.

Retention of liquid contaminants in layered soils

Observations of organic contaminant liquids retained in layered soil profiles indicate contaminant saturations much greater than residual, where residual saturation would be expected, if one assumes a static distribution of fluid pressure. It is theorized that the increased retention of fluid is caused by coarse soil layers that reach a very small unsaturated hydraulic conductivity early in the drainage process, and thus prevent further drainage. The results from a retention experiment in a one-dimensional column were used to test this hypothesis. A vertical column was dry packed with a layer of fine sand (high entry pressure head) overlaying a layer of coarse sand (low entry pressure head). The column was saturated with an organic liquid and then drained. The saturation and pressure profiles were monitored over an extended period of time. A dual-gamma system was used to determine the liquid saturation, and specially fitted ring tensiometers were used to measure the capillary pressure at selected points along the column. The pressure readings and saturation profiles showed a high retention of oil in the fine layer above the interface of the two soils. The profiles were compared first with static pressure and corresponding saturation profiles, and secondly with profiles calculated assuming a very small steady flow through the column. The experimental profiles closely resemble those profiles that assume small flow rates, and display a much higher retention above coarse layers than the static profiles.

Experimental Study of the Gelation Behavior of a Polyacrylamide/Aluminum Citrate Colloidal-Dispersion Gel System

Summary The gelation behavior of a polyacrylamide/aluminum citrate colloidal-dispersion gel (CDG) system was investigated in sandpacks at frontal advance rates of 2 ft/D. A gelatinous mass formed where the gelant encountered a change in flow medium. Permeabilities of homogeneous media were reduced only by factors that were similar to those obtained with a polymer displacement alone. A laboratory investigation of a polyacrylamide/aluminum citrate CDG system was conducted to determine whether the system develops in-depth permeability modification in unconsolidated sandpacks. The study includes flow of the polymer and in-situ gelation behavior of the gelant in porous media and aggregate growth during the gelation reaction in beakers. Flow experiments were conducted in long unconsolidated sandpacks in which the gel solution was mixed in-line before injection. Injection rates were designed to provide adequate residence time for the gel solution to develop in-situ flow resistance during displacements based on bulk gel characterization tests. Residual resistance factors were determined following a static rest period in which the sandpack was left saturated with the injected gel solution. For comparison, apparent viscosity and residual resistance factors were also determined for the polymer flowing through unconsolidated sandpacks. Membrane dialysis was used to study the aggregate size distribution of the gel system at selected times after mixing. In-depth in-situ flow resistance did not develop when the gelling solution was injected into the sandpacks at frontal advance rates of 2 ft/D. Propagation through the sandpack was similar to a polymer solution. Flow resistance was characterized by the formation of a gelatinous filter cake, which formed when the injected solution encountered a change in flow medium, such as a screen placed at the ends to retain sand in place, the interface between the 50-mesh coarse sand layer at the inlet and the rest of the sandpack, and void spaces. Delaying injection by 2 hours after mixing in-line (to simulate field conditions) resulted in severe front-end stripping of gel aggregates. In all cases, residual resistance factors for the gel solution were similar to those obtained with a polymer displacement alone. Effluent fractions from gel solution displacements never developed a gel structure, and their viscosities were significantly lower than the injected solution. In the study of gel size distribution, aggregates were not detected at reaction times of 4 and 8 hours.

Soil Heating for Enhanced Remediation of Chlorinated Solvents: A Laboratory Study on Resistive Heating and Vapor Extraction in a Silty, Low-Permeable Soil Contaminated with Trichloroethylene

Thermally enhanced remediation of trichloroethylene (TCE) from a 50 cm deep silty soil was demonstrated in a two-dimensional laboratory tank. Volatilized TCE was captured by vapor extraction in an overlaying coarse sand layer. Soil vapor extraction was first tested alone at 23 °C, showing very little efficiency due to the low-permeable layer and an estimated cleanup time of more than 1 year. By injecting electric current, the temperature was increased to 85 and 100 °C in steps, and the fluxes of TCE increased by factors of 2.6 and 19, respectively. After 37 days of heating, the mass of TCE in the soil was reduced from 35 to 0.072 g, corresponding to 99.8% mass removal. Average soil TCE concentrations were reduced from 273 to 0.6 mg/kg. Steam production by boiling of pore water and a 9-fold increase in the Henry's law constant of TCE were identified as the major mechanisms for overcoming mass-transfer limitations. The silty soil did not dry out due to water addition at the current electrodes, which is promising for the use of thermal enhancements forremediation of water-saturated clay layers and in shallow groundwater. In-situ thermal cleanups can be done in a few months, at costs typically below $100/m3, and with very high removal efficiency for volatile and semivolatile organ ics.

The isolation of Kruunuvuorenlampi, southern Finland, and implications for Holocene shore displacement models of the Finnish south coast

In the southern coastal area of Finland, many studies exist on shore displacements related to the higher Ancylus Lake and Litorina Sea altitudes. However, the late- Holocene shore displacement history is much less known and the shore displacement models are based on interpolations. Kruunuvuorenlampi, a small lake located at an altitude of 8.6 m a.s.l., was studied to test the reliability of the interpolated models. The cores revealed an unusual bottom lithostratigraphy, with a coarse gravel and sand layer sandwiched between the lower marine clays and upper shallow-water clay-gyttja. Analysis of diatoms, pollen and loss-on-ignition, together with radiocarbon datings, were carried out to determine and date the isolation event of the lake. The results show that the lake was isolated ca. 2400 14C years BP and that the coarse grained layer was deposited prior to the isolation. The reconstruction of the emergence of the lake basin area suggests that the coarse grained layer originated from strong wave erosion of the shores before the isolation. This interpretation is supported by the presence of a wave-washed boulder belt on the NE slope of the basin. The isolation of Kruunuvuorenlampi lies exactly on the interpolated shore displacement model of the 30 m Litorina isobase. This placement suggests that no significant transgressions took place between the Litorina transgression and the isolation of Kruunuvuorenlampi.

Infiltration and Redistribution of Perchloroethylene in Stratified Water‐Saturated Porous Media

AbstractAlthough infiltration, redistribution, and drainage of dense nonaqueous‐phase liquids (DNAPLs) in water‐saturated soils and aquifers are known to be sensitive to stratifications of the solid phases of the porous media, little experimental evidence is available to explain the behavior of DNAPL movement. To improve our understanding of DNAPL movement under these conditions, physical simulations were conducted with various perchloroethylene (PCE) spills in initially water‐saturated, stratified porous media in nominally one‐dimensional glass columns and in an intermediate scale, nominally two‐dimensional laboratory flow container. The columns and flow container were packed with two distinct layers of coarse sand, with a fine sand layer in between. Volumetric water and DNAPL contents, as well as bulk densities, were determined with a dual‐energy gamma radiation system. To obtain additional information required for the explanation of the displacement processes, in‐ and outflow rates of water and PCE were measured during each experiment. In the sand columns, PCE accumulated on top of the fine layer, while in the flow container, considerable lateral movement was observed just above the fine sand layer. In general, these phenomena were attributed to the small conductivity values of the fine layers relative to those of the coarse layers rather than to displacement pressures not being exceeded. Overall our results suggest that in field situations, continuous PCE spills are more likely to penetrate horizontal fine layers than short intermittent spills.