Preferential Water Flow Research Articles

Water Flow Path Characterization in Shallow Vadose Zone Using Tensiometers

In this project, we will present the findings of a study using Tensiometer systems designed to investigate the water flow path pattern in shallow vadose zone. The purpose of this paper is to evaluate water flow path in shallow vadose zone and to calculate the infiltration rate and hydraulic conductivity of a soil using Tensiometer. We have measured the subsurface water flow paths in sandy clay loam soil following infiltration experiment using Tensiometers. The matric potential and hydraulic conductivity measurements show that subsequent infiltration and water movement in unsaturated (vadose) zone are vertical, but it can have large lateral component under steady condition. This shows that water moves generally from high water content to lower water content region. Average pressure head for the percolation test conduction locations EB and HB was -30 and -80 cm respectively. Hysteresis produces another interesting situation when the soil is drained. We found that the wetter portion of the soil in vadose zone could be at a lower potential (head) than the dryer portions, resulting in lateral driving force for a preferential flow of water from the dryer to the wet soil. The infiltration rate for the 5 cm ponded water was calculated at 5.45 cm/hr. The infiltration rate curve shows that the rate of infiltration decreases with the time. When infiltration first starts, the wetting front is steep and very close to the surface. Similarly, due to the pressure head gradient, large value for infiltration is recorded. Under these conditions, we believe that the gradient in pressure head is responsible for the rapid movement of water into the dry soil. The effect of gravity is less on water during the initial stages of infiltration; however, it is more effective for preferential flow pattern. In the latter infiltration event, the wetting front has moved deeper into the soil. As a result, the pressure head gradient at the surface is much smaller and consequently has little effect. When the pressure head is equal zero, infiltration rate approaches almost to the lowest level. We also observed that even a minor change in soil-water pressure due to slope could change both direction and magnitude of water flux.

Domestic Wastewater Depuration Using a Horizontal Subsurface Flow Constructed Wetland and Theoretical Surface Optimization: A Case Study under Dry Mediterranean Climate

The wastewater generated by isolated houses without access to public sewers can cause environmental problems, like the contamination of aquifers with nitrates and phosphates, as occurs in southeastern Spain. The effectiveness of a previously built horizontal subsurface flow constructed wetland (HF-CW) was studied over two years as a possible solution. This HF-CW measured 27 m2; it was planted with Phragmites australis(Cav.) Trin. Ex Steuds sp. Altissima and the parameters studied were those required by European Union (EU) legislation and adopted by Spain. Average abatement efficiency rates, for the first and the second year of study, were: biochemical oxygen demand over five days (BOD5) (96.4%, 92.0%), chemical oxygen demand (COD) (84.6%, 77.7%), total suspended solids(TSS) (94.8%,89.9%),total nitrogen(TN)(79.5%,66.0%),ammonium nitrogen(NH4+-N)(98.8%, 86.6%) and total phosphorous (TP) (83.7%, 82.8%). Average abatement efficiency for nitrate nitrogen (NO3−-N) (−1280.5%, −961.1%) and nitrite nitrogen (NO2−-N) (−5.8%, −40.0%) were negative because its content in influent wastewater was very low and they appear mainly from influent NH4+-N, as a result of purification processes carried out in the HF-CW bed. The abatement rates make the system suitable to produce discharges into the environment in accordance with Spanish law. It is noteworthy that the HF-CW patch suffered an episode of bed drying during the summer of 2013, whereby the causes were related to system oversizing and high evapotranspiration in the area. As a consequence, the decrease in the abatement of water pollutants during the second year can be attributed to the creation of preferential water flow paths and short circuits through the constructed wetland (CW) bed. As a result of the oversizing of the CW, a theoretical resizing based on BOD5, TSS, TN or TP is proposed. The calculated values for the redesign were: 5.22 m2 considering DBO5, 0.18 m2 considering TSS, 10.14 m2 considering TN and 23.83 m2 considering TP. Considering the area where the HF-CW was located and in accordance with Spanish law for non-sensitive areas (no TN or TP requirements for wastewater discharge), BOD5 is the most appropriate parameter for design; it is 5.2 times lower than the HF-CW initially built and without risk of bed drying.

Exploring water cycle dynamics by sampling multiple stable water isotope pools in a developed landscape in Germany

Abstract. A dual stable water isotope (δ2H and δ18O) study was conducted in the developed (managed) landscape of the Schwingbach catchment (Germany). The 2-year weekly to biweekly measurements of precipitation, stream, and groundwater isotopes revealed that surface and groundwater are isotopically disconnected from the annual precipitation cycle but showed bidirectional interactions between each other. Apparently, snowmelt played a fundamental role for groundwater recharge explaining the observed differences to precipitation δ values. A spatially distributed snapshot sampling of soil water isotopes at two soil depths at 52 sampling points across different land uses (arable land, forest, and grassland) revealed that topsoil isotopic signatures were similar to the precipitation input signal. Preferential water flow paths occurred under forested soils, explaining the isotopic similarities between top- and subsoil isotopic signatures. Due to human-impacted agricultural land use (tilling and compression) of arable and grassland soils, water delivery to the deeper soil layers was reduced, resulting in significant different isotopic signatures. However, the land use influence became less pronounced with depth and soil water approached groundwater δ values. Seasonally tracing stable water isotopes through soil profiles showed that the influence of new percolating soil water decreased with depth as no remarkable seasonality in soil isotopic signatures was obvious at depths > 0.9 m and constant values were observed through space and time. Since classic isotope evaluation methods such as transfer-function-based mean transit time calculations did not provide a good fit between the observed and calculated data, we established a hydrological model to estimate spatially distributed groundwater ages and flow directions within the Vollnkirchener Bach subcatchment. Our model revealed that complex age dynamics exist within the subcatchment and that much of the runoff must has been stored for much longer than event water (average water age is 16 years). Tracing stable water isotopes through the water cycle in combination with our hydrological model was valuable for determining interactions between different water cycle components and unravelling age dynamics within the study area. This knowledge can further improve catchment-specific process understanding of developed, human-impacted landscapes.

Impact of Preferential and Lateral Flows of Water on Single‐Ring Measured Infiltration Process and Its Analysis

Core Ideas A special device was developed to visually display the infiltration process. Impacts of preferential and lateral flow on infiltration rates were measured. Mathematical models were derived to correct the measured infiltration rates. The corrected infiltration processes agreed well with the 1D values. To improve the measurement accuracy of the soil infiltration rate, we studied the effects of preferential flow caused by the gap between the soil profile and the ring wall during its installation and lateral flow induced by the three‐dimensional impact of a single ring on the infiltration process. Laboratory experiments using silt loam taken from Beijing were conducted with a device designed to produce a soil profile that could visually display water movement during infiltration in the soil. Observations of the wetted soil profile inside and under the halved ring during the infiltration process were used to partition rates from the soil surface, preferential flow, and lateral movement of water. Mathematical models were derived to correct the measured infiltration rates affected by preferential and lateral flows during the initial and steady infiltration stages. Results indicated that in the initial infiltration stage (0–17 min), the preferential flow significantly increased the measured infiltration rates. Error caused by preferential flow ranged from 207 to 121%. In the following infiltration stage (17–120 min), the contribution of lateral flow ranged from 21 to 77%. Steady infiltration rates estimated with the modified model were 7% higher than those of one‐dimensional infiltration rates, and saturated hydraulic conductivities measured by single ring infiltrometer were 15% higher than rates estimated by the constant head method, which may have been caused by higher static water pressure inside the ring caused by preferential flow passage. This study offers a new analysis of ponded single‐ring infiltrometer data.

Mapped Fractures and Sinkholes in the Coastal Plain of Florida and Georgia to Infer Environmental Impacts from Aquifer Storage and Recovery (ASR) and Supply Wells in the Regional Karst Floridan Aquifer System

The regional Floridan aquifer system (FAS) extends from the submerged carbonate platform of the Atlantic Ocean, Gulf of Mexico, and Straits of Florida in the southeastern United States (US), throughout Florida and the coastal plain of Alabama, Georgia, and South Carolina. This carbonate aquifer system is characterized by bedding planes, fractures, dissolution cavities, and other karst features that result in preferential flow of ground water, particularly in response to anthropogenic perturbations such as groundwater withdrawals and aquifer injections. The FAS was divided into six sub-regions for groundwater-modeling purposes in 1989, with results concluding that breaches of those groundwater divides had occurred and those breaches were attributed to large withdrawals of ground water in the US southeastern coastal plain. Those results suggest the model did not elucidate preferential flow conditions through fractures and other karst conduits. We hypothesized that incorporating fractures and sinkholes into groundwater models could improve results and predict adverse impacts to environmentally sensitive areas. We analyzed extensive fracture networks and sinkholes previously mapped throughout Florida and in Dougherty County, Georgia. Some of those fractures extend from one sub-region into an adjacent sub-region of the FAS and may be facilitating the breaching of groundwater divides described in the 1989 groundwater model for this regional aquifer system. The greater total fractures and fracture density in Dougherty County (1,225 and 141.3/100 km2, respectively) compared to 21 north-Florida counties (10-91fractures per county and 0.6-3.8/100 km2, respectively) presumably is due to the scale of fracture mapping and shorter mean lengths of mapped fractures in Dougherty County (1.2 km), compared to north Florida counties (26-118 km), rather than to orders of magnitude increases in fracture densities in that part of the FAS. The number of sinkholes identified in Dougherty County in a recent, unrelated project using 2011 Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images, was approximately an order of magnitude greater than the number of sinkholes mapped in analog form in that county and published in 1986. Extension of the dense network of those fractures that occurred within the boundaries of a Priority Amphibian and Reptile Conservation Area (PARCA) that encompassed Dougherty County covered the Elmodel Wildlife Management Area (WMA) and ASR demonstration well in Baker County, Georgia. Those extensions also passed through numerous agricultural areas with center-pivot irrigation wells in southwest Georgia; intersected other Georgia PARCAs near the Florida-Georgia state line; and clumped in two areas of dense sinkhole clusters in northwest Florida. No determination has been made regarding the contributions of pirated water from the Apalachicola-Chattahoochee-Flint (ACF) River Basins and Wakulla Springshed from the magnitude and extent of agricultural, municipal, and industrial groundwater withdrawals in Georgia’s coastal plain, that exceed groundwater withdrawals in Florida for that area of the FAS, to the increase in sinkholes in Dougherty County and the dense clusters of sinkholes in northwest Florida, via preferential flow through fractures. Similarly, the survival and recovery of at least 24 animal species in Georgia that are either federally listed or high-priority state species may be jeopardized by adverse direct, indirect, and cumulative impacts from preferential flow through fractures, sinkholes, and other karst conduits in response to aquifer injections and withdrawals that have not been evaluated. Currently no regional groundwater model has been constructed to evaluate such preferential groundwater flow in the FAS. A model incorporating preferential flow via mapped fractures and sinkholes is essential to determine the magnitude and extent of environmental impacts from ASR wells and other supply and disposal wells in this regional aquifer system, such as pirated water from the ACF and other river basins, alterations in submarine groundwater discharge to Apalachicola Bay and other coastal areas, saltwater intrusion, upconing of saline ground water and resulting impacts to federally endangered and threatened species and high-priority state species.

Simulated Preferential Water Flow and Solute Transport in Shrinking Soils

We present follow‐up work to previous work extending the classical rigid (RGD) approach formerly proposed by Gerke and van Genuchten, to account for shrinking effects (SHR) in modeling water flow and solute transport in dual‐permeability porous media. In this study we considered three SHR scenarios, assuming that aggregate shrinkage may change either: (i) the hydraulic properties of the two pore domains, (ii) their relative fractions, or (iii) both hydraulic properties and fractions of the two domains. The objective was to compare simulation results obtained under the RGD and the SHR assumptions to illustrate the impact of matrix volume changes on water storage, water fluxes, and solute concentrations during an infiltration process bringing an initially dry soil to saturation and a drainage process starting from an initially saturated soil. For an infiltration process, the simulated wetting front and the solute concentration propagation velocity, as well as the water fluxes and water and solute exchange rates, for the three SHR scenarios significantly deviated from the RGD. By contrast, relatively similar water content profiles evolved under all scenarios during drying. Overall, compared to the RGD approach, the effect of changing the hydraulic properties and the weight of the two domains according to the shrinkage behavior of the soil aggregates induced a much more rapid response in terms of water fluxes and solute travel times, as well as a larger and deeper water and solute transfer from the fractures to the matrix during wetting processes.

Fractures as Preferential Flowpaths for Aquifer Storage and Recovery (ASR) Injections and Withdrawals: Implications for Environmentally Sensitive Near-Shore Waters, Wetlands of the Greater Everglades Basin and the Regional Karst Floridan Aquifer System

In theory, “aquifer storage and recovery” (ASR) is a form of artificial aquifer recharge consisting of threecomponents: (1) aquifer injections of fluids; (2) withdrawals of the injected fluids; and (3) a period of timebetween the injections and withdrawals that is considered to be aquifer “storage” of the injected fluids. Theinjected fluids may be: (1) treated sewage effluent (also known as reclaimed, reuse, or bright water); (2)stormwater runoff pumped out of canals, mine pits or other areas; (3) surface waters from natural lakes andstreams; or (4) ground water from different aquifer zones. An evaluation of existing data from more than 80injection/withdrawal cycle tests at 18 ASR sites in 9 counties throughout southern Florida, in the regional karstFloridan aquifer system of the United States (US) revealed that less than 25% actual “recovery” was achievedfrom ASR wells where water from various sources was injected into the regional karst aquifer system.Determination of actual “recovery” was based on the reported chloride content of injected and recovered waterand was more suggestive of fluid disposal than aquifer “recharge.” Actual “recovery” for those ASR tests,adjusted to the chloride concentrations of injected fluids, ranged from 0-17% for “storage” periods that rangedfrom 0-181 days. Although results of actual “recovery” provide little support for the concept of “stored” water, inreality those results also over-estimate the volume of injected water that is stored because it assumes that waterrecovered at the same chloride concentration is the same water that was injected. There is no evidence in theASR data to support that assumption. The low actual “recovery” rates occurred despite the fact that 28 of thecycle tests had a “storage” period < 1 day and the longest “storage” period tested did not exceed 181 days. Thosebrief “storage” periods also were insufficient to meet the stated agency objectives of retrieving the injected fluidsduring the dry season, more than six months after injection of what is termed “excess water” during the rainyseason. Despite those results, the agency’s Final Technical Data Report (TDR) and groundwater model releasedin 2014 concluded that: (1) “recovery” from those wells would range from 70-100% and (2) 232 ASR wells (94in the upper Floridan aquifer, 37 in the Avon Park Permeable Zone of the middle Florida aquifer and 101 in theBoulder Zone) could be completed in Florida’s Greater Everglades Basin (basin) as restoration. That Final TDRdid not consider differences in chloride content between water that was injected into and withdrawn from theASR cycle tests and that groundwater model for the basin did not include the anisotropy option or preferentialflow through karst conduits such as fractures. Preferential flow of water injected and withdrawn could result inboth low ASR “recovery” rates and environmental harm, such as submarine groundwater discharge (SGD)contaminated with pollutants, including nutrients that result in harmful algal blooms (HABs). That TDR andgroundwater model for southern Florida also did not evaluate the direct, indirect or cumulative adverse impactsof preferential flow from ASR injections and withdrawals (e.g., through fractures) on federally threatened andendangered species, environmentally sensitive areas or on sinkhole formation. Our evaluation of the basinvicinity also included analyses of fracture frequency, length and proximity to ASR wells, other injection andwithdrawal wells and modern sinkholes, based on georeferenced and transformed lineaments from threeindependent sources: the US Army Corps of Engineers (ACOE, 2004c), Florida Department of Transportation(FDOT, 1973), and Vernon (1951). Based on the three lineament data sets included in our study, includingwww.ccsenet.org/jgg Journal of Geography and Geology Vol. 7, No. 2; 2015118fractures that extend for considerable distances through environmentally sensitive areas in the basin such as theBig Cypress National Preserve, Biscayne National Park, Estero Bay, Everglades National Park, Florida KeysNational Marine Sanctuary, Indian River Lagoon and Marquesas Keys Wildlife Management Area. Some ofthese fractures also extend beyond the boundaries of the basin.

The origin and reversible nature of poultry litter biochar hydrophobicity.

Transient changes in wettability complicate the prediction of biochar's hydrologic effects. Biochar wetting properties were characterized from poultry litter biochar (PLBC) produced from slow pyrolysis at temperatures between 300 and 600°C with water drop penetration time (persistence of hydrophobicity) and contact angle (CA; severity of hydrophobicity) measurements. Hydrophobicity was associated with semivolatile organic compounds coating PLBC surfaces, which resulted in 24.4 carbon layers and CAs of 101.1 ± 2.9° at a pyrolysis temperature of 300°C but only 0.4 layers of surface coverage and CAs of 20.6 ± 1.3° when pyrolyzed at 600°C. Mixing PLBC with water removed organic coatings, and storage in water for 72 h decreased CA as much as 81° for the most hydrophobic PLBCs. When mixed with quartz sand of the same particle size, CAs of PLBC-sand mixtures increased from 6.6 ± 1.4° at 0% PLBC mass fraction to 48.3 ± 2.0° at 15% mass fraction. Hydrophobic and hydrophilic PLBCs increased CA by nearly identical amounts at 2 and 5% mass fractions, which was explained by the influence of PLBC particle topology on macroscopic surface roughness of PLBC-sand mixtures. For environmentally relevant situations, PLBC-sand mixtures at mass fractions ≤15% remained water wetting. However, all PLBC additions increased CA, which may alter infiltration rates and induce preferential water flow.

Bacteria viability and decay in water and soil of vertical subsurface flow constructed wetlands

In this study the functional status of bacterial biomass within a vertical subsurface flow (VSSF) constructed wetland was examined with the aim to understand the relationship between viable and dead bacteria in soil and influent/effluent wastewater and elucidate the large amount of dead cells in the soil which may affect the long-term behavior of the system. The quantification of viable and dead bacteria in influent and effluent wastewater and in the soil of a VSSF was performed at single-cell level by flow cytometry (FCM). An optimised pre-treatment was applied to soil samples using sodium pyrophosphate and ultrasonication at a specific energy of 80kJ/L. Viable and dead cells were detected on the basis of cellular membrane integrity coupling SYBR-Green I and Propidium Iodide. The bacteria profile in the VSSF soil depends on the depth and the material grain size. In the upper 0–10cm sand layer the number of total bacteria per gram of dry weight (DW) was higher (1.82×109 cells/gDW) than in the deeper 40–50cm (4.8×108 cells/gDW) probably due to the vertical feeding and a sieving effect of influent in the top layers. Bacterial biomass in the entire VSSF depth was 0.082mgVSS/gDW or 144gVSS/m3 (per cubic meter of VSSF bed). Size of viable bacteria in the VSSF was smaller (0.16μm3/cell) than typical size of activated sludge (0.23μm3/cell), due to lower nutrient conditions and a longer retention time of viable bacteria in the bed, estimated at around 130 days by mass balance. Dead bacteria were prevalent in the VSSF soil with a viable/dead bacteria ratio (V/D) of 0.52. The content of dead bacteria might be higher in the soil due to the presence of unsaturated zones not reached by fresh influent wastewater (“dead-zones”), where moisture and substrate are not so available and bacteria may die. Conversely, the higher V/D ratio (3.3) in the effluent reflects the enrichment of wastewater with viable bacteria during the passage through the VSSF bed and along preferential water flow, with higher water content and substrate availability, where the bacterial growth is favored.

Increased profile wettability in texture-contrast soils from clay delving: case studies in South Australia

Clay delving is becoming a popular practice to increase productivity of texture-contrast soils in southern Australia. The practice brings subsoil clay to the surface to be mixed with the sandy topsoil, and unlike clay spreading, it combines the addition of hydrophilic material with a ripping effect that disrupts the sharp boundary between the sandy topsoil and clayey subsoil. Our objective was to evaluate the magnitude of effects caused by delving on the spatial distribution of water through the profile for three Sodosols (Stagnic Solonetz soils) in the south-east of South Australia. We also wished to evaluate the extent to which clay delving might reduce water ponding at the A–B horizon interface. We wetted both delved and undelved texture-contrast soils with a Brilliant Blue dye solution under initially dry and wet conditions (to evaluate the effect of antecedent water content), and then took digital images of the stained profiles for quantitative comparison of the wetted areas. The stained soil profiles indicated that clay delving reduced preferential water flow (finger flow) and resulted in deeper and more uniform wetting of the A horizon, particularly under initially dry conditions. Under wet conditions (where water repellence was largely overcome), finger flow was significantly reduced regardless of delving but it still occurred to varying degrees depending on site characteristics. Delving significantly reduced ponding of water at the A–B horizon boundary and allowed greater penetration into the B horizon. At all sites, greater effects occurred directly on the delving lines and diminished with distance, implying that closer spacing of delving tines would increase uniformity of wetting throughout the profile. The effectiveness of delving on profile wetting was highly variable across the three sites, indicating that the outcome depends inter alia on the intrinsic soil characteristics and the delving equipment used in the field.

Closure to “Laboratory and Field Calibration of the Diviner 2000 Probe in Two Types of Soil” by J. Haberland, R. Gálvez, C. Kremer, and C. Carter

The authors deal with the quite interesting and actual problem of Diviner 2000 capacitance probe calibration and present some field and laboratory data obtained on two different layers (0–0.26 and 0.26–0.50 cm) of the same soil profile, characterized by different textural class. The importance of site-specific calibration of sensors used to monitor soil or plant water status assumes a particular relevance in semiarid environments where the application of precision irrigation represents an appropriate management strategy aimed to achieve high values of water use efficiency (Cammalleri et al. 2013). Moreover, in clay soils, physical properties are strongly influenced by soil water content (Provenzano et al. 2013), so that the correct measurement of this variable plays a key role to increasing crop yield and preserving water. However, the discussers would focus on some significant points to be corrected in the manuscript and some others that should have been specified in the methodology and considered in the final discussion, as following specified, for the benefit of potential readers. The need to adequately install the access tube, aimed to ensure the contact between the tube and the surrounding soil, is not only to avoid preferential flow of water down the walls of the tube, as considered in the paper, but also to reduce the air gap around the tube and to avoid rough measurements of scaled frequency, used to estimate soil water contents, whose values depend on the mutual proportion of soil, water, and air in the soil volume investigated by the sensor. With reference to the second part of Eq. (2) of original paper, it is necessary to precise that the function θwðSFÞ correctly results

New Analytical Model for Cumulative Infiltration into Dual-Permeability Soils

In the vadose zone, preferential flow and transport are much more common than uniform water flow and solute transport. In recent decades, several models have been developed for preferential water flow and physical non equilibrium solute transport. Among these models, the dual-permeability approach is an interesting tool for the conceptualization and modeling of preferential flow. However, this approach has been mainly studied from a numerical point of view. In this study, we developed a new analytical model for water infiltration into dual-permeability soils. The model is based on the analytical model originally proposed for single-permeability soils. The proposed model relies on the assumption that the water exchange rate at the interface between the matrix and fast-flow regions does not change cumu lative infiltration at the soil surface, so that the total cumulative infiltration can be set equal to the sum of independent cumulative infiltrations into each region. This assumption was investigated using numerically generated data. The proposed analytical model was then used to evaluate the effects of fast-flow region hydraulic properties and hydraulic conditions on total cumulative infiltration for the case of single- and multi-tension water infiltra tion experiments. Finally, both single- and dual-permeability models were evaluated with respect to their ability to fit experimental data and associ ated problems of non-uniqueness in optimized parameters. The proposed model could serve as a new tool for modeling and characterizing preferential flow in the vadose zone.

Layer-by-Layer Assembly of Zeolite/Polyelectrolyte Nanocomposite Membranes with High Zeolite Loading

Incorporation of zeolite nanoparticles into nanocomposite membranes is advantageous with respect to enhancing membrane permeability by providing preferential water flow paths through the subnanometer porous structure of zeolite while maintaining excellent separation capability. We present a layer-by-layer assembly approach to effectively incorporate zeolite nanoparticles into nanocomposite membranes. Negatively charged Linde type A (LTA) zeolite nanoparticles were sandwiched between two different polyelectrolyte layers, negatively charged poly(acrylic acid) (PAA) and positively charged polyethylenimine (PEI), to form a PEI–LTA–PAA trilayer. The zeolite loading in the multitrilayer membranes was between 30 and 60 wt %, which is attributed to the drastically improved compatibility between zeolite and polymers, a direct result of electrostatic interactions. The performance of the trilayer membrane was compared with that of a control PEI–PAA bilayer membrane in a forward osmosis membrane system. The incorpora...

Influence of measurement conditions on the resolution of electrical resistivity imaging: The example of abandoned mining dams in the La Carolina District (Southern Spain)

The La Carolina district, which is located in Jaen (Southern Spain), has experienced important mining activity for centuries. These long-standing mining activities, which have been associated with the presence of a philonian network of metallic sulfides, have generated vast accumulations of mine wastes—primarily tailings impoundments—that contain high levels of heavy metals from ore concentration plants. In this paper, the resolution of electrical resistivity imaging (ERI) is analyzed to determine the internal structure of these tailings dams and to assess the influence of the tailings over groundwater and surface water. The “La Manzana” dam, which is one of the largest sludge dams in the district, was selected to achieve this objective.First, old aerial photographs that were taken prior to the existence of the tailings dam were examined. Second, probing was performed using mechanical drilling, which enabled the identification of the features of the fill material, the thicknesses of the mine tailings and the contact zone between the mining structure and the basement. Third, the probe acts as a piezometer, which is an excellent tool to correlate the geophysical prospecting techniques. The characterization of the internal geometry of this structure has been performed by two ERI surveys, in which electric profiles were obtained under different moisture conditions. During the dry season, this methodology has been effective for identifying the morphology of the structures, contact with the substratum, variations in the vertical and horizontal distribution of the deposited material, and the fracture zones, as well as the contact between the tailings and the substratum on which they are deposited. Conversely, during the wet season, this contact was not distinct in the profile; however, variations in the saturation degree of these deposits, preferential infiltration areas and water flow through the interior of the tailings dam were observed. Last, the ERI survey confirmed the absence of waterproofing measures in the dump areas, which represents a high risk of soil and water pollution in the surrounding areas.

Effects of Soil Water Repellency on Moisture Patterns in a Degraded Sapric Histosol

AbstractAn understanding of soil moisture content variability is fundamental in hydrological studies of peat soils, whose preservation depend on water‐related processes. Dehydration of fens and adapting them for agricultural production have contributed to the degradation of peat soils. The goal of this study was to determine how the critical soil moisture content (CSMC) and soil water repellency (SWR) affect soil moisture patterns in a degraded peat‐muck soil profile. SWR was measured under laboratory conditions using the water drop penetration time test, and then the CSMC was assessed. An investigation of moisture patterns was based on soil moisture data collected over short distances in a grass‐covered peat‐muck soil profile on seven dates. Observed differences in moisture patterns demonstrate that the CSMC can be used for the prediction of preferential flow occurrences in peat‐muck soils. Lower values of the CSMC and lower levels of SWR persistence in muck layers than in peat layers indicate that degradation of peat soils improves their wettability. The relatively low values of CSMC and the low shrinkage potential in the muck layer suggest that preferential water flow in the degraded organic soils can occur when heavy rains are preceded by long periods of summer drought. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Infiltration and Drainage Analysis in a Heterogeneous Soil by Electrical Resistivity Tomography

Petrocalcic horizons are a common feature of soils in many regions. As a result of their presence, the soils acquire a noticeable stratified profile that may severely restrict water infiltration. Therefore, assessing infiltration and drainage becomes a complex task due to the heterogeneous nature of these kind of soils. In the present study, infiltration and drainage were evaluated by means of electrical resistivity tomography (ERT) in a Paleudol soil with a petrocalcic horizon at 90 cm depth. A field infiltration test was performed on an 11.2-m-long transect that was implemented with tensiometers and time domain reflectometry (TDR) probes. Successive measurements using ERT allowed determining resistivity changes as infiltration progressed. Resistivity values were converted into soil water content values by means of functions obtained after laboratory experiments. The soil water contents calculated were validated with the numerical modeling of pressure heads and with TDR water contents. The results showed soil horizon heterogeneities and the behavior of the preferential flow of water. These results further demonstrated the strong control that petrocalcic horizon heterogeneities exert on the water flow at field scale. Less indurated zones favored preferential flow to develop.

DESARROLLO DE REPELENCIA AL AGUA EN SUELOS AFECTADOS POR INCENDIOS, EN UNA ZONA DEL PARQUE METROPOLITANO DEL DISTRITO METROPOLITANO DE QUITO

&lt;p&gt;La exposición del suelo a temperaturas altas durante la ocurrencia de un incendio forestal, puede inducir el desarrollo de repelencia al agua y otros efectos que alteran la calidad del suelo, entre los que destacan: cambios en el contenido de carbono y de materia orgánica, pérdida de suelo, aparecimiento de flujos preferenciales y erosión. En este trabajo se determinó la severidad y persistencia de la repelencia al agua alcanzada por un suelo previamente quemado dentro de una zona de 13,4 has en el Parque Metropolitano en la Ciudad de Quito. La determinación de la persistencia de la repelencia al agua del suelo se realizó utilizando la metodología de tiempo de penetración de una gota de agua (WDPT) y la severidad de la repelencia se determinó utilizando el test de molaridad de etanol (MED). Los valores más altos de persistencia a la repelencia al agua, fueron determinados a los cuatro meses de haber ocurrido el incendio y permitieron clasificar al suelo afectado por fuego como “Fuertemente Repelente”. Se observó que la persistencia de la repelencia inducida por el fuego fue transitoria y disminuyó con relación al tiempo, determinándose un decremento de la repelencia en las muestras analizadas a los siete y nueve meses. No se encontró una relación definitiva entre el incremento de la repelencia al agua y el aumento de la materia orgánica, que presentó el promedio de concentración más alta a los cuatro meses de ocurrido el incendio (5,88 %).&lt;/p&gt;

Concentrações de metais em solo ocupado por cemitério - uso da técnica de espectrometria de fluorescência de raios-x por energia dispersiva - EDXRF

O estudo de contaminação de solos e dos recursos hídricos superficiais e/ou subterrâneos por cemitérios é uma área ainda recente no meio científico. O principal contaminante é o necrochorume gerado a partir do processo de decomposição dos corpos humanos, ao longo de um período de tempo. Este estudo teve como objetivo, determinar a faixa de variação da concentração de alguns metais em perfis de solos. Utilizou-se a técnica de Fluorescência de Espectrometria de Energia Dispersiva de Raios X (EDXRF), avaliados em 70 amostras de solos. A área estudada foi um cemitério, localizado na cidade de Seberi, no noroeste do Estado do Rio Grande do Sul, na Bacia do Paraná, em Latossolos vermelho alumino férrico, originados do intemperismo de rochas vulcânicas, do tipo basaltos formadoras do Sistema Aquífero Serra Geral/SASG. A seleção dos pontos de amostragem foi estimada a partir do fluxo preferencial de água de superfície, usando-se o método matemático de interpolação krigagem. Foram considerados 10 pontos de coletas, distribuídos entre a superfície do terreno até a profundidade de 300 cm, em materiais com matriz argilosa até pedregosa no horizonte C. Os metais Alumínio e Ferro e o metalóide Vanádio, apresentaram concentrações variadas nas diversas profundidades do perfil do solo.

VARIAÇÃO ESPACIAL DAS CONCENTRAÇÕES DE CÁDMIO E MANGANÊS EM SOLO OCUPADO POR ATERRO SANITÁRIO

Landfills are configured as a correct and safe way of disposal of solid waste, but require serious study for your choice. Therefore this study aimed to determine the potential for contamination of soil by cadmium and manganese as a result of the occupation by landfill. In the present study, there was a borehole to collect the samples being made according to the existing topography at the site and preferential flow of surface water, considering 10 collection points called P1 to P10. Analyses were performed by Shimadzu Energy Dispersion X-ray Fluorescence Spectrometer Rany, Serie EDX-720. Manganese showed high levels at all points studied with P4 at the highest concentration to 200 cm (11576.46 mg kg-1) has the lowest concentration shown in P7 was 300 cm (516 237 mg kg-1) due high concentration of this element, it becomes harmful to the soil and vegetation at the site. As for Cadmium higher concentrations occurred at P7 at 100 cm depth (57238 mg kg-1) and P9 at 300 cm depth (36319 mg kg-1). Based on this, it was concluded that the highest concentrations of cadmium occurred at depths ranging from 100 to 200 cm, showing that there was an increased concentration with depth. Already vulnerability has been classified as low, thus presenting little susceptible to contamination of groundwater.

Shot-clay MX-80 bentonite: An assessment of the hydro-mechanical behaviour

This study presents the results of an experimental study conducted to characterise the hydro-mechanical behaviour of shot-clay MX-80 bentonite. In the shot-clay process, granular bentonite was mixed continuously with water and shot on the walls of a tunnel section at the Grimsel Underground Research Laboratory (URL), in Switzerland. The shot-clay was placed to create a layer of bentonite in direct contact with the host rock to avoid preferential water and/or gas flow along the tunnel wall. Samples for an experimental programme were collected during the shooting. The index properties, microstructural features, swelling potential and water retention properties of the shot-clay were analysed. An experiment was then conducted under controlled total suction to analyse the hydro-mechanical behaviour of the material along a predefined stress path involving suction and confining stress variations. Based on the results of this test, the expected behaviour of the shot-clay bentonite when subjected to the environmental conditions in the repository was determined. The test results were compared with data on the observed behaviour of compacted MX-80 granular bentonite to assess the effects of the shot-clay emplacement technique on the behaviour of the MX-80 bentonite. The results highlight the role of the emplacement dry density on the behaviour of bentonite.