Water Mound Research Articles

Areal artificial recharge has changed the interactions between surface water and groundwater

Artificial groundwater recharge is increasingly utilized globally for addressing regional groundwater issues due to its effectiveness and ease of application. However, due to the complexity of the interaction of groundwater systems with the external environment and its inherent latency, governance effects are difficult to quantify and are not fully understood yet. In this study, the efficiency of areal artificial groundwater recharge was determined and the interactions with surface water were analyzed by field surveys, sample analysis, water balance reconstruction, and model simulation. A typical groundwater recharge region in the Beijing-Tianjin-Hebei region, China, was focused. Additionally, the response of groundwater flow and water quality to areal artificial groundwater recharge was quantified. Results showed that areal artificial groundwater recharge changes the relationship between surface water and groundwater, with an efficiency of 70 % under high recharge and fluctuation, and decreasing to 20–30 % after the groundwater level was stabilized. The impact on the hydrodynamic field were primarily manifested as the formation of water mounds near river channels, which expand laterally up to 9.2 km from the recharging river channel one year after implementation.Then the impact increases to 14.9 km and continues to expend a year after cessation. The areal artificial groundwater recharge has simultaneously improved the water quality by 23 % in monitoring wells within a 10 km distance from the river channel. The results of this study quantify the impacts of area artificial recharge on groundwater and provide references for the improvement of water resources and water environment in those similar regions.

A novel ADE system with tunable droplet size and ejection height

Acoustic droplet ejection (ADE) has been proven to move liquids in droplet form from a container to mid-air. However, the droplet sizes produced using the traditional ADE setups are proportional to their heights if the physical framework is unchanged. This limitation obstructs further employment of ADE technology since having the exact sizes of droplets at a specific location or different sizes at different locations is required for many applications. To overcome this limitation and enable more possible applications of ADE, this study proposed an innovative ADE configuration that could manipulate the size and height of the ADE droplets with only electrical signals. To achieve this, a low-voltage driving period and a pinhole structure were added to create a water mound before ejection. First, simulations were conducted to validate the proposed method and find the parameters of the novel ADE setup. After that, a driving circuit featuring a high-voltage pulser and a field-programmable gate array was built. However, a 3D spherical resin model was printed to focus the acoustic wave on the water surface, and a cover with a pinhole was added to create water mound. To observe the behavior of the droplets, a recording system and detection algorithm were developed to capture and identify the dimension/height of the droplets, respectively. Finally, the proposed ADE configuration successfully manipulated the droplet size at the same ejecting height under three driving voltages (65, 70, and 75 V) and pinhole diameters (3.7, 4, and 4.4 mm).

Aerodynamic/Hydrodynamic Investigation of Water Cross-Over for a Bionic Unmanned Aquatic-Aerial Amphibious Vehicle.

An aerodynamic/hydrodynamic investigation of water cross-over is performed for a bionic unmanned aquatic-aerial amphibious vehicle (bionic UAAV). According to flying fish features and UAAV flight requirements of water cross-over, the bionic conceptual design of crossing over water is described and planned in multiple stages and modes of motion. A solution procedure for the numerical simulation method, based on a modified SST turbulence model and the VOF model, is expressed, and a verification study is presented using a typical case. Longitudinal-lateral numerical simulation analysis investigates the cruise performance underwater and in the air. The numerical simulation and principal experiment verification are conducted for crossing over water and water surface acceleration. The results indicate that the bionic UAAV has an excellent aerodynamic/hydrodynamic performance and variant configuration to adapt to water cross-over. The bionic UAAV has good water and air navigation stability, and the cruise flying lift-drag ratio is greater than 15 at a low Reynolds number. Its pitching moment has the phenomenon of a "water mound" forming and breaking at the water cross-over process. The present method and the bionic variant configuration provide a feasible water cross-over design and analysis strategy for bionic UAAVs.

Suitability of containerized toxicant to control Solenopsis invicta (Hymenoptera: Formicidae) threatening cave species in Bexar County, Texas.

Several protected troglobitic invertebrate species are known to occur in caves on Joint Base San Antonio-Camp Bullis, Bexar County, Texas, United States. The United States Fish and Wildlife Service (USFWS) identified red-imported fire ant Solenopsis invicta (hereafter RIFA) (Buren 1972) as the primary threat to cave species' nutrient sources, cave crickets, Ceuthophilus secretus (Scudder 1894). Per the service's recommendations, Joint Base San Antonio-Camp Bullis currently implements boiling water mound injections with digging for RIFA control. However, treatment effectiveness is highly variable and largely dependent on the time of day, weather, and personnel diligence. Toxicants have been used for RIFA treatment throughout the world, but concerns exist that traditional applications of toxicant bait around caves might be accessible and inadvertently affect nontarget arthropods, including cricket populations. To mitigate this accessibility, physically limiting access to the toxicant from crickets may be an option. Our objectives were to (i) compare and evaluate the effectiveness of Amdro (Hydramethylnon) and Advion (Indoxacarb) granular baits housed in Ants-No-More Bait Stations (Kness MFG. Inc., Albia, IA) and (ii) evaluate the distance of effectiveness of each bait within a bait station. Ultimately, we observed a 98% reduction in RIFA mound abundance from both baits. Additionally, RIFA mounds within 10 m of the containerized toxicant were reduced by 70%. Our pilot study suggested that Ants-No-More Bait Stations are an effective way to reduce RIFA mounds by 70% if placed 10 m from each other. In practice, this could include bait stations completely covering a particular distance to a cave entrance or fewer bait stations in a ring barrier at a single radial distance to a cave entrance. Containerized toxicants may be a cost-effective and safe RIFA control option around protected cave environments, but further studies are needed to determine potential effects on nontarget arthropods, optimal bait station configuration, and potential effects of biomagnification.

Recent and New Information from the Slug Test Data of Ferris and Knowles (1954)

Abstract The slug test theories take into account or not the tested material storativity, S. Ferris and Knowles (1954) proposed a first theory with S, the Ferris-Knowles (FK) theory. A few reasons were given to reject it in the 1970s. New and stronger reasons are given here. The FK test was incomplete because the data started 75 seconds after slugging with a large volume of water. These data are reinterpreted here with recent and correct methods, which have proven that the theories with S are wrong and cannot give an S value. The FK partial data yield a straight velocity plot, typical of all slug tests in aquifers, and a small piezometric error of 1 cm. During the first 75 seconds, 99 % of the water volume left the riser pipe to enter the aquifer. The only data (t > 75 s) were for the last 1 % of the water volume. The article shows that the FK theory yields an elastic S value corresponding to peat, which is nonsense. If the authors tested an aquifer, then their late data described the return to equilibrium of a water mound due to slugging 150 L of water and not the slug test data, which took place in the first 75 seconds. The delay in starting data collection may have been due to long dynamic effects with gas trapping and outgassing after slugging with a huge volume of water, but this was not documented. The correct methods for slug tests show that the FK theory tries to fit an exponential with a hyperbola. The FK theory was the first of weird methods trying to find the S value with confusing math and physics, which have so far delayed the use of physically correct methods in ASTM standards for slug tests.

Impact of major nearshore land reclamation project on offshore groundwater system

Offshore groundwater (OG) systems are widely distributed in the coastal areas, where nearshore land reclamation projects are constructed for seaports, airports, and urban other infrastructures. However, there is almost no study on the interaction between these projects and the OG system. This paper presents the first such an effort using the Hong Kong International Airport near Lantau Island, as a case study by developing a three-dimensional density-dependent flow and transport model to investigate the interaction between the reclaimed airport and the OG system. Results show that the offshore relatively fresh groundwater may flow from the nearby Lantau Island through the submarine confined aquifer. The higher pore water pressure in the basal aquifer beneath the airport is generated by the regional groundwater system of the nearby Lantau Island. Besides, the reclaimed airport also serves as extra aquifer space for the storage of fresh groundwater resources. The expansion of the 3rd runway will further increase the water table and move the center of the water mound toward the 3rd runway area. The groundwater system in the airport will reach a new steady state 50 years after the expansion, and the volume of the fresh groundwater lens is calculated to be ~5.2 × 107 m3 with a maximum water table of 1.4 m above mean sea level. The findings of this study have implications on the large-scale nearshore land reclamation which may be affected by the OG system in other coastal areas.

Bore Impact on Decks of Coastal Structures

Bore impact on horizontal fixed decks of coastal structures is studied by use of the Level I Green–Naghdi (GN) equations and the Navier–Stokes (NS) equations. The bore is generated by the breaking of a water reservoir, and may represent the propagation of a tsunami on land or broken storm waves. The bore-induced horizontal and vertical forces are determined and their variation with the bore and deck conditions is studied in this work. Various conditions of deck location with respect to the water level are considered, including cases with the deck under or above the still-water level. Two types of bore are considered, namely (i) a bore generated by a dam break, where the reservoir water depth is substantially larger than the downstream depth, and (ii) a bore generated by an initial mound of water, where the reservoir water depth is comparable to the downstream depth. It is shown that these mechanisms result in the formation of significantly different bore shapes. It is also shown that the relative height of the reservoir and the downstream water depth play a significant role in the bore generation and its impact on coastal structures. It is also found that the bore-induced forces vary almost linearly with the change in amplitude of the reservoir, while a change in the length of the reservoir has little effect on the loads. The horizontal force on submerged decks is shown to be independent of the submergence depth of the deck; this is due to the uniform velocity distribution over the water column of the bore. Results of the GN and NS models are compared with each other for submerged cases and the limitations, accuracy, and efficiency of these models in studying this problem are discussed. Results of the GN equations are in close agreement with the NS equations, making them a computationally efficient alternative for the study of this problem.

Effect of multilayered groundwater mounds on water dynamics beneath a recharge basin: Numerical simulation and assessment of surface injection

AbstractInteractions between groundwater mounds caused by a geologic layer contrast affect the efficiency of managed aquifer recharge in arid areas. However, research has rarely examined the roles of groundwater mounding size variations on soil water dynamics in a stratified vadose zone in response to a sustained infiltration source. Numerical experiments were conducted on a two‐dimensional vertical‐section domain using HYDRUS software to simulate the behaviours of two adjacent (upper and lower) groundwater mounds underlying an infiltration basin subjected to clay loam and sandy alternately‐layered soil profiles. The model successfully predicted the volume and extent of perched water and approximated vertical travel times during events generating downward fluxes from the surface injection. The response time of the mounding width (lateral extension) to the surface injection was delayed as compared to that of the mounding height (vertical extension), especially for the lower water mound. The mounding heights and widths show a strongly positive correlation with the infiltration rates of both high‐ and low‐permeability layers where the injected water mounded, while the water storage amounts in the high‐ and low‐permeability layers were governed by the mounding height and width, respectively. Exploratory simulations were then employed to assess the dependence of groundwater mounding behaviours and recharge performances on surface injection strategies. Results suggest that, by reducing injection rate or shortening injection duration, the near‐term fraction of the surface injection converted to deep recharge is likely to be increased due to the narrowed groundwater mounding size, which would be limited by the water‐retarding effect of layer contrasts. This study has important implications for predicting and understanding multilayered groundwater mounding behaviours and associated water mass balance under the geologic stratification, and is expected to aid in optimizing the infiltration basin operation for aquifer recharge.

Severe wave run-ups on fixed surface-piercing square column under focused waves

Severe wave run-ups on a surface-piercing column leading to strong uprush water jets may cause unexpected impact loads on offshore structures. To reveal the underlying mechanism related to the complicated wave–column interaction, this paper investigates the occurrence and evolution of wave run-ups on a fixed surface-piercing square column under focused waves experimentally and numerically by comparing the wave run-up profiles, wave loads on the column, and velocity and pressure fields in the cases of different peak periods and steepnesses. The results manifested that the wave run-up under a very steep focused wave is significantly influenced by the localized nonlinear interaction between the wave crest and the uplifted water mound in front of the column and experiences a different regime from those primarily due to nonlinear wave diffraction. In the cases of breaking or nearly breaking focused waves, the sudden change in the fluid velocity on the wave crest when impacting on the uplifted water mound dramatically increases the peak value and gradient of dynamic pressure in the adjacent region and hence results in critical impact load on the column and strong accelerating effect of the uprush flow. Additionally, a larger peak period can further increase the thickness (or volume) of the uprush flow, potentially increasing the damage risk of offshore structures.

Simulation of Two Dimensional Subsurface Seepage Flow In Isolated Anisotropic Aquifer

Mathematical models have emerged as important tools for prediction of transient and steady state behavior of water table in unconfined aquifer under seepage and recharge condition. This paper presents analytical solution to predict the behavior of water table in anisotropic unconfined aquifer overlaying a leaky base in response to multiple recharge and withdrawal. The hydrological setting consists of rectangular aquifer with all four sides with no flow conditions. The aquifer is subjected to recharge and withdrawal activities through multiple recharge basin and extraction/injection wells. The subsurface seepage flow is approximated by two-dimensional Boussinesq equation and solved using Fourier cosine transform. Application of closed form solution is demonstrated using an illustrative example. Effect of aquifer parameter on formation of ground water mound and cone of depression due to recharge and withdrawal are discussed. The influence of permeability on the mound height and cone depth is also analyzed.

On Bore Dynamics and Pressure: RANS, Green-Naghdi, and Saint-Venant Equations

AbstractPropagation and impact of two- and three-dimensional bores generated by breaking of a water reservoir is studies by use of three theoretical models. These include the Reynolds-averaged Navier–Stokes (RANS) equations, the level I Green-Naghdi (GN) equations, and the Saint-Venant (SV) equations. Two types of bore generations are considered, namely, (i) bore generated by dam-break, where the reservoir water depth is substantially larger than the downstream water depth, and (ii) bore generated by an initial mound of water, where the reservoir water depth is larger but comparable to the downstream water depth. Each of these conditions corresponds to different natural phenomena. This study shows that the relative water depth plays a significant role on the bore shape, stability, and impact. Particular attention is given to the bore pressure on horizontal and vertical surfaces. The effect of fluid viscosity is studied by use of different turbulence closure models. Both two- and three-dimensional computations are performed to study their effect on bore dynamics. Results of the theoretical models are compared with each other and with available laboratory experiments. Information is provided on bore kinematics and dynamics predicted by each of these models. Discussion is given on the assumptions made by each model and differences in their results. In summary, SV equations have substantially simplified the physics of the problem, while results of the GN equations compare well with the RANS equations, with incomparable computational cost. RANS equations provide further details about the physics of the problem.

Numerical Simulation of the water-exit process of the missile based on Moving Particle Semi-Implicit method

The phenomenon of a water mound can show up in the process of water-exit of the missile [1], and the a water mound will break and splash in a very short time, which will exert an extra force on the missile and therefore will affects the movement of the missile as well as the gesture when the missile comes out the water. Therefore, investigation into the water-exit process of the missile is of great significance to the launch of the underwater missiles. The traditional grid methods always fail to simulate the whole the water-exit process because of the large deformation of the mesh. The paper adopts a meshless method, called Moving Particle Semi-Implicit method (MPS), to study the water-exit process of the missile. Based on verifying it by the dam break simulation, MPS is applied to simulate the water mound during the water-exit process, which is aiming at providing some reference for the relevant theoretical research.

Programming and evaluation of the 2D Hantush analytical solution for artificial recharge of aquifers

The method of artificial recharge of aquifers represents an opportunity to answer many problems related to the management of water resources, especially in arid and semi-arid regions. However, before installation and management of water infiltration, structures require planning in the design through forecasting tools, which can simulate scenarios of evolution of the hydraulic mound formed under this charging device. In this context, several analytical solutions have been developed (Baumann in Trans ASCE 117:1024–1060, 1952; Glover in Mathematical derivations as pertain to ground-water recharge. In: United States Department of Agriculture, western soil and water management research branch, Fort Collins, Colorado, 1960; Hantush in Water Resour Res 3(1):227–234, 1967; Hunt in J Hydraul Div 97(7):1017–1030, 1971; Marino in Growth and decay of ground-water ridges in response to deep percolation. MS thesis, New Mexico Institute of Mining and Technology, Socorro, New Mexico, 1965, J Res Geophys 72:1195, 1967; Rao and Sarma in Groundwater 19(3):270–274, 1981) and others, which predict the evolution of the hydraulic mound and its geometry from input parameters which represent some properties of the aquifer and recharge control data. We have proposed for this work, a detailed study of the analytical solution of Hantush (1967), through a comparison with experimental data of Bianchi and Haskell in (Field observations of transient ground water mounds produced by artificial recharge into an unconfined aquifer. In: USDA Agricultural Research Services Rapport ARS W-27, p 27, 1975), a sensitivity study of the different input parameters of the model such as the geometry of the Infiltration basin, hydraulic conductivity, storage coefficient, recharge rate and saturated aquifer thickness. Finally, we did a case study of this applied model to the Mnasra basin, in the northwest of Morocco. The solution shows reasonable estimates of the evolution of the hydraulic mound, and could be a good forecasting tool; however, the non-respect of the initial assumptions of the model, such as the homogeneity of the soil, can induce some errors in the estimation of the height and shape of the hydraulic mound.

Microbial Biomarker Transition in High-Altitude Sinter Mounds From El Tatio (Chile) Through Different Stages of Hydrothermal Activity.

Geothermal springs support microbial communities at elevated temperatures in an ecosystem with high preservation potential that makes them interesting analogs for early evolution of the biogeosphere. The El Tatio geysers field in the Atacama Desert has astrobiological relevance due to the unique occurrence of geothermal features with steep hydrothermal gradients in an otherwise high altitude, hyper-arid environment. We present here results of our multidisciplinary field and molecular study of biogeochemical evidence for habitability and preservation in silica sinter at El Tatio. We sampled three morphologically similar geyser mounds characterized by differences in water activity (i.e., episodic liquid water, steam, and inactive geyser lacking hydrothermal activity). Multiple approaches were employed to determine (past and present) biological signatures and dominant metabolism. Lipid biomarkers indicated relative abundance of thermophiles (dicarboxylic acids) and sulfate reducing bacteria (branched carboxylic acids) in the sinter collected from the liquid water mound; photosynthetic microorganisms such as cyanobacteria (alkanes and isoprenoids) in the steam sinter mound; and archaea (squalane and crocetane) as well as purple sulfur bacteria (cyclopropyl acids) in the dry sinter from the inactive geyser. The three sinter structures preserved biosignatures representative of primary (thermophilic) and secondary (including endoliths and environmental contaminants) microbial communities. Sequencing of environmental 16S rRNA genes and immuno-assays generally corroborated the lipid-based microbial identification. The multiplex immunoassays and the compound-specific isotopic analysis of carboxylic acids, alkanols, and alkanes indicated that the principal microbial pathway for carbon fixation in the three sinter mounds was through the Calvin cycle, with a relative larger contribution of the reductive acetyl-CoA pathway in the dry system. Other inferred metabolic traits varied from the liquid mound (iron and sulfur chemistry), to the steam mound (nitrogen cycle), to the dry mound (perchlorate reduction). The combined results revealed different stages of colonization that reflect differences in the lifetime of the mounds, where primary communities dominated the biosignatures preserved in sinters from the still active geysers (liquid and steam mounds), in contrast to the surviving metabolisms and microbial communities at the end of lifetime of the inactive geothermal mound.

3D survey and modelling of shipwrecks in different underwater environments

Abstract Experiments carried out by a combined team of the Ca’ Foscari and IUAV Universities of Venice, on ancient shipwrecks with different characteristics in different environments (shallow water cargoes of marble stones and a deep water mound of amphoras), confirm the potential of three-dimensional surveys in documenting underwater archaeological sites. Multi-image photogrammetry is the principal and innovative technique used, but we have confirmed the necessity of accompanying this new system with a precise topographical net. This last aspect is particularly evident when it is necessary to solve the problem of the documentation of a multi-strata mound of amphoras, anchoring 3D models of each stratum as it is removed. Photogrammetric models must be processed with 3D software modelling to interpret the textured meshes and to construct polygonal models, selecting the important aspects of the objects, and eliminating the ‘noise’ of the point cloud. The 3D model can easily be used to reconstruct the original arrangement of the cargo, on which it is then possible to make various calculations and considerations of nautical engineering.

Enhancing Subsurface Drainage to Control Salinity in Dryland Agriculture

Abstract. Controlling the physical processes of soil salinization involves lowering ground water levels, draining the vadose zones, and leaching excess salts from root zones. Plastic drain tubing strategically placed 1.5 to 1.8 m below the surface in semiarid lands can lower water tables and drain phreatic water, but irrigation is usually required to satisfactorily leach the offending salts. In non-irrigated drylands, the leaching process depends on natural precipitation, but the drier the climate, the greater the need for more leaching water. Possible practices which tap complementary water in conjunction with subsurface drainage include: (1) establishment of roughness barriers to trap wind-borne snow, and (2) pumping water from near-surface, ground water mounds. The mean electrical conductivity of saturated soil paste extracts sampled yearly from a semiarid site in Saskatchewan averaged 14.1 dS m-1 during the six years before the drainage was installed, 13.0 dS m-1 for two years just after drainage but before capturing blowing snow, and 9.6 dS m-1 for the six years following. The average barley grain harvested during the six years prior to drainage yielded 330 kg ha-1 and 2414 kg ha-1 after installation of the enhanced drainage system. In a follow-up sub-study, fall applications of 4.6 dS m-1 mounded ground water from a shallow well fitted with a solar-powered pump within a drainage system preceded spring seeding of alfalfa. Enhanced drainage improved mean seedling emergence from 20% to 79%. Every 28 mm of ground water applied, up to 2273 mm, increased alfalfa emergence by 1%. Keywords: Agricultural drainage, Plant emergence, Pre-seeding irrigation, Solar-powered pumping, Soil reclamation, Soil salinity, Windbreaks.

On some solitary and cnoidal wave diffraction solutions of the Green–Naghdi equations

Nonlinear waves of the solitary and cnoidal types are studied in constant and variable water depths by use of the Irrotational Green–Naghdi (IGN) equations of different levels and the original Green–Naghdi (GN) equations (Level I). These equations, especially the IGN equations, have been established more recently than the classical water wave equations, therefore, only a handful applications of the equations are available. Moreover, their accuracies and the conditions under which they are applicable need to be studied. As a result, we consider a number of surface wave propagation and scattering problems that include soliton propagation and fission over a bump and onto a shelf, colliding solitons, soliton generation by an initial mound of water and diffraction of cnoidal waves due to a submerged bottom shelf, and compare the predictions with experimental data when available.

Regional and local patterns in depth to water table, hydrochemistry and peat properties of bogs and their laggs in coastal British Columbia

Abstract. In restoration planning for damaged raised bogs, the lagg at the bog margin is often not given considerable weight and is sometimes disregarded entirely. However, the lagg is critical for the proper functioning of the bog, as it supports the water mound in the bog. In order to include the lagg in a restoration plan for a raised bog, it is necessary to understand the hydrological characteristics and functions of this rarely studied transition zone. We studied 13 coastal British Columbia (BC) bogs and identified two different gradients in depth to water table, hydrochemistry and peat properties: (1) a local bog expanse–bog margin gradient, and (2) a regional gradient related to climate and proximity to the ocean. Depth to water table generally increased across the transition from bog expanse to bog margin. In the bog expanse, pH was above 4.2 in the Pacific Oceanic wetland region (cooler and wetter climate) and below 4.3 in the Pacific Temperate wetland region (warmer and drier climate). Both pH and pH-corrected electrical conductivity increased significantly across the transition from bog expanse to bog margin, though not in all cases. Na+ and Mg2+ concentrations were generally highest in exposed, oceanic bogs and lower in inland bogs. Ash content in peat samples increased across the bog expanse–bog margin transition, and appears to be a useful abiotic indicator of the location of the bog margin. The observed variation in the hydrological and hydrochemical gradients across the bog expanse–bog margin transition highlights both local and regional diversity of bogs and their associated laggs.

NUMERICAL SOLUTION OF BOUSSINESQ EQUATION ARISING IN ONE-DIMENSIONAL INFILTRATION PHENOMENON BY USING FINITE DIFFERENCE METHOD

Infiltration is a gradual flow or movement of groun dwater into and through the pores of an unsaturated porous medium (soil). The fluid infiltered in porous medium (unsaturated soil ), its velocity decreases as soil becomes saturated , and such phenomena is called infiltration. The present model deals with the filt ration of an incompressible fluid (typically, water ) through a porous stratum, the main problem in groundwater infiltration. The present model was developed first by Boussinesq in 1903 and is related to original motivation of Darcy. The mathematical formulation oinfiltration phenomenon leads to a non-linear Boussinesq equation. In the present paper, a numerical solution of Boussinesq e quation has been obtained by using finite differenc e method. The numerical results for a specific set of initial and boundary conditio ns are obtained for determining the height of the fsurface or water mound. The moment infiltrated water enters in unsaturated soil ; the infiltered water will start developing a curv e between saturated porous medium and unsaturated porous medium, which is call ed water table or water mound. Crank-Nicolson finite difference scheme has been applied to obtain the required results for var ious values of time. The obtained numerical results resemble well with the physical phenomena. When water is infiltered through the ve rtical permeable wall in unsaturated porous medium the height of the free surface steadily and uniformly decreases due to the saturat ion of infiltered water as time increases. Forward finite difference scheme is conditionally stable. In the present paper, the gra phical representation shows that Crank-Nicolson fin ite difference scheme is unconditionally stable. Numerical solution of the g overning equation and graphical presentation has be en obtained by using MATLAB coding.

Emerging Contaminant Sources and Fate in Recharged Treated Wastewater, Lake Havasu City, Arizona

In 2008, Lake Havasu City, Arizona, began a treated wastewater subsurface recharge program at its North Regional Wastewater Treatment Plant (NRP) to store treated wastewater, which is planned to be seasonally recovered for irrigation during the summer months. As a proactive measure, the city decided to monitor a suite of pharmaceuticals and other emerging contaminants (PECs) along with required regulatory constituents, e.g., nitrate. Potential contributing sources of PECs throughout the water system were identified, resulting in only six constituents detected in the untreated drinking water and treated drinking water, all at concentrations less than 50 ng/L. Thirty-three of 40 PECs analyzed were identified in the city9s treated wastewater streams, with concentrations ranging from just above the detection level to 9000 ng/L (pseudoephedrine), clearly showing the dominating local urban use of these compounds. NRP treated wastewater is recharged via vadose zone injection wells. It migrates through alluvial fans sediments, some containing interstitial clays, forming a water mound and blending with groundwater of the Colorado River Aquifer. Sixteen of 33 PECs present in the NRP treated wastewater have concentrations above detection limits (>10 ng/L) within 150 m (492 ft) of the injection wells. Six PECs (sulfamethoxazole, carbamazepine, primidone, phenytoin, N,N-diethyl-meta-toluamide [DEET], and meprobamate) remained above their respective detection limit in monitoring wells that penetrate sediments largely free of clay more than 560 m (1,840 ft) away from the injection wells.