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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Water Budget Analysis and Groundwater Inverse Modeling

Farid Marandi, Sayena 2012 May 1900 (has links)
The thesis contains two studies: First is the water budget analysis using the groundwater modeling and next is the groundwater modeling using the MCMC scheme. The case study for the water budget analysis was the Norman Landfill site in Oklahoma with a quite complex hydrology. This site contains a wetland that controls the groundwater-surface water interaction. This study reports a simulation study for better understanding of the local water balance at the landfill site using MODFLOW-2000. Inputs to the model are based on local climate, soil, geology, vegetation and seasonal hydrological dynamics of the system to determine the groundwater-surface water interaction, water balance components in various hydrologic reservoirs, and the complexity and seasonality of local/regional hydrological processes. The model involved a transient two- dimensional hydrogeological simulation of the multi-layered aquifer. In the second part of the thesis, a Markov Chain Monte Carlo (MCMC) method were developed to estimate the hydraulic conductivity field conditioned on the measurements of hydraulic conductivity and hydraulic head for saturated flow in randomly heterogeneous porous media. The groundwater modeling approach was found to be efficient in identifying the dominant hydrological processes at the Norman Landfill site including evapotranspiration, recharge, and regional groundwater flow and groundwater-surface water interaction. The MCMC scheme also proved to be a robust tool for the inverse groundwater modeling but its strength depends on the precision of the prior covariance matrix.
2

Accurate Cylindrical-Coordinate Numerical Models For The Analysis Of Hydrologic Tests

Keller, John Edward 01 January 2009 (has links)
Analytical solutions to well hydraulic problems have restrictive assumptions that often do not match real world conditions. Although numerical models more closely match reality, they either ran too slowly to be practical or lacked accuracy because of coarse grid spacing and large time steps. Advances in computer power over the last few decades now allow for accurate, fast numerical models that handle complex flow systems. The purpose of this dissertation was to develop flexible and accurate numerical modeling codes for the simulation of hydrologic tests. One of these numerical modeling codes, the Slug Test Simulator (STS), was designed for the mechanics of a single well test, or slug test. STS can handle a variety of conditions including unconfined flow, partial penetration, layered heterogeneities, and the presence of a homogeneous well skin like existing codes. This program also extends on the capabilities of earlier codes with its ability to simulate a heterogeneous skin where K can vary in both the radial and vertical directions. STS has a clear user interface, can display graphical results, and allows the user to determine hydraulic conductivity through a trial-and-error curve-matching process. Comparisons of STS to the Cooper-Bredehoeft-Papadopulos analytical solution and the Kansas Geological Survey (KGS) semi-analytical solution produced near-identical curves under a wide variety of conditions. Numerous analytical studies have shown that the well skin is an important factor in the underestimation of hydraulic conductivity in slug tests. STS allows for the exploration of the well skin issue under conditions too complex for analytical models. Model trials revealed two key discoveries: 1) if any layers within the skin have the same hydraulic conductivity as the surrounding formation, flow is concentrated within these conduits and the resultant head response approaches the case when no skin is present; and 2) the two most important properties in determining the overall influence of the skin are specific storage and skin thickness. The first discovery suggests that extensive development activities can essentially eliminate any well skin impacts. Other factors such as partial penetration, the placement of the well screen, and anisotropy play insignificant roles in resultant head responses. Recent research is focusing on alternative direct- push (DP) methodologies to determine hydrologic properties. DP offers advantages over traditional well tests, but may yield inaccurate results if the screen becomes clogged during pushing activities. The Kansas Geological Survey (KGS) developed a new DP technique, the Direct-Push Permeameter (DPP), to overcome this limitation. Existing analytical or numerical models cannot address the specialized nature of DPP tests so a second numerical modeling code, the Direct Push Permeameter Simulator (DPSS), was developed. DPPS was generated by modifying STS so both numerical codes are similar in many ways, particularly with their flexibility and accuracy. The codes differ in how they handle vertical layering, the boundary conditions at the well, and the spreadsheet interfaces. DPPS was able to produce near-identical curves in comparison to the Theis analytical solution. DPPS was also able to reasonably recreate DPP field data conducted at two sites with distinctly different media properties. The GEMS and Nauen sites had an average error of 14.2% and 3.1%, respectively between the field data and DPPS simulations.
3

ANALYSIS AND MODELING OF NON-DARCIAN FLOW IN GROUNDWATER WITH MODFLOW CFP

Adhikari, Roshan 01 December 2014 (has links)
Conventional methods of groundwater modeling are based on applying laminar flow condition in the aquifer and assuming primary porosity to be present in the aquifer. But in cases where conduits, caves, springs and sinks characterize the aquifer as in karst, this assumption is inappropriate. In addition to Darcian flow condition in matrix portion of aquifer there should be consideration for dealing with non-Darcian flow in the conduits where high velocity of flow occurs. Presence of conduit network in the aquifer greatly affects the potentiometric heads within the aquifer. Hence the necessity of different modeling method has long been realized for karst aquifers. MODFLOW-Conduit Flow Process (CFP) has the capability to simulate both turbulent and laminar groundwater flow condition present in caves and conduits portion of karst aquifers. This study examined the cases where a sub-regional model was used to simulate discharge of springs and heads both with and without considering the presence of conduit network in the aquifer using MODFLOW-CFP 2005 and MODFLOW 2005 respectively. Comparison of results showed that the potentiometric head in the area consisting conduit network were unrealistically low when conduit network was not considered to be present in the matrix. This study also introduces and uses a program called CONGEN to generate conduit flow process file for CFP Mode 1. Furthermore this study also carried out the benchmark testing to examine the capability of MODFLOW-CFP to simulate both laminar and turbulent pipe flow in the conduits for a sub-regional scale. Results from transient state simulation indicate that, although MODFLOW-CFP considers both laminar and turbulent flow conditions in the pipe like conduits in the karst, it underestimated the peak discharge of the springs in this study.
4

Groundwater Modeling of Managed Aquifer Recharge at the Regional and Local Scale

Frazier, Andrew Dane 09 June 2022 (has links)
The Hampton Roads Sanitation District is heading a Managed Aquifer Recharge project designed to build water resiliency for the district as well as meet recent regulations concerning effluent released into the Chesapeake Bay. The Sustainable Water Initiative for Tomorrow (SWIFT) project will include five injection well fields across the Virginian Coast. The first of these fields to be implemented is the James River site, scheduled to begin in 2025. A model of the Virginia Coastal Plain region was created in 2009 and has been used to simulate the combined impact of the full-scale SWIFT project. This study estimated the change in hydraulic head in the Potomac Aquifer System caused by the proposed James River recharge well field at a regional and local level. That estimation required the use of a widely accepted model of the Virginia Coastal Plain developed in 2009 which was subjected to a limited validation using USGS monitoring well data for comparison. That model was then used to establish boundary conditions for a local scale model surrounding the James River site, after which each model was used to run four pumping scenarios with varying rates of recharge. The validation of the Virginia Coastal Plain model found it to be satisfactory for the scope of this work, and it was therefore used to interpolate boundary conditions for the developed local model. The regional and local model both showed an increase in the simulated head values of the Potomac Aquifer System. The regional model simulated a sharper initial increase than the local model, however, long term the local model simulated a greater impact to the groundwater levels from the proposed recharge. / Master of Science / The Potomac Aquifer System (PAS) is a main water source for most of eastern Virginia and high pumping rates have caused notable drawdown in several areas. The Hampton Roads Sanitation District (HRSD) has initiated the Sustainable Water Initiative for Tomorrow (SWIFT) project that is designed to alleviate the stress on the PAS by artificially recharging the PAS through injection well. A regional groundwater model, built in 2009, has been used to estimate the impact of the proposed recharge for the SWIFT project at full capacity. This work validated the use of the regional model within the region of the first proposed SWIFT well field at the James River Site. Once the validation was complete, the regional model provided a framework to develop a more detailed model on a smaller scale. That model was then used to simulate the proposed injection well field at varying rates to estimate the effect of the James River Site. This study has shown that the regional model provides an adequate framework to build local scale models. The simulations run in both the regional and local models found that the proposed recharge increases the water levels in the PAS immediately surrounding the well field and that the impact is felt to distances exceeding 50 miles after 10 years.
5

Grundvattenmodellering inom Loddby före detta Sulfitmassabruk

Bachofner Gran, Clara January 2019 (has links)
Loddby sulfitmassabruk var under sin verksamhetstid beläget vid Loddbyviken, cirka fem kilometer norr om Norrköping. På bruket bedrevs tillverkning av sulfitmassa mellan år 1899 och 1977 inom ett område som omfattar 18,6 hektar. Det före detta sulfitmassabruket anses idag vara förorenat till den grad att det medför en mycket stor risk för människors hälsa och miljön, men för att kunna besluta om åtgärder gällande den förorenade marken vid Loddby f.d. sulfitmassabruk behöver bland annat de hydrogeologiska förhållandena inom området klargöras. Detta examensarbete syftade till att kartlägga grundvattenströmningen vid Loddby f.d. sulfitmassabruk genom att utveckla en platsspecifik grundvattenmodell med modellkoden MODFLOW i programvaran Groundwater Modeling System (GMS). Dessutom avsåg examensarbetet att undersöka hur grundvattenströmningen i området påverkas av fluktuationer i den intilliggande Loddbyvikens vattennivå. Initialt utvecklades en konceptuell modell för området, där det hydrologiska systemet förenklat beskrevs med avseende på områdets geologi, hydrologi och klimat. Modellområdet avgränsades utefter topografiska vattendelare samt hydrologiska gränser och delades sedan vertikalt in i tre lager utefter de huvudsakliga jordmaterial som hade identifierats vid undersökningar i området: fyllnadsmaterial, lera och morän. I GMS delades modellområdet sedan in i ett rutnät med storleken 5x5 meter och dess ränder tilldelades lämpliga randvillkor. Genom att interpolera utsträckningen av modellens tre lager från sonderingspunkter med känd geologi kunde den konceptuella modellen beskrivas matematiskt i programvaran. För att öka modellens tillförlitlighet kalibrerades jordmaterialens hydrauliska konduktiviteter mot observerade grundvattennivåer i flertalet grundvattenrör inom Loddby f.d. sulfitmassabruk. Efter kalibrering var fyllnadsmaterialets, lerans samt moränens hydrauliska konduktivitet 2,1ˑ10-4 m/s, 5,7ˑ10-7 m/s respektive 3,9ˑ10-5 m/s. En känslighetsanalys utfördes slutligen för att undersöka hur valet av värden på jordmaterialens hydrauliska konduktiviteter samt grundvattenbildningen påverkar modellresultaten. Simuleringarna med den kalibrerade modellen visade bland annat att grundvattnet generellt rör sig från områdets västra delar mot Pjältån och Loddbyviken i norr och öster, dock runt de områden där bergytan når höga nivåer. Förändringar i Loddbyvikens vattennivå visade sig ha en viss påverkan på mängden vatten i systemet, men bedömdes inte medföra en större effekt på strömningsmönstret i området. Känslighetsanalysen visade att modellen var mycket känslig för värdet på grundvattenbildningen, samt att även den hydrauliska konduktiviteten för moränen hade en stor effekt på resultatet. Ett lågt värde på lerans genomsläpplighet visade sig kunna leda till modelleringssvårigheter och fyllnadsmaterialets konduktivitet hade generellt en liten påverkan på resultatet. / Loddby sulphite pulp factory was during its active days located next to Loddbyviken, approximately five kilometers north of Norrköping. Production of sulphite paper pulp was conducted between the years 1899 and 1977 within an area of 18,6 hectares. The former sulphite pulp factory is today considered polluted to the extent that it is entailing a great risk for human health and the environment, but to be able to decide what measures to take, the hydrogeological conditions in the area need to be clarified. The objective of this master’s thesis was to map the groundwater flow pattern within Loddby former sulphite pulp factory by developing a site-specific groundwater model with the groundwater flow model MODFLOW in the software Groundwater Modeling System (GMS). The master’s thesis also aimed at examining how the groundwater movement in the area is affected by fluctuations in the water level of Loddbyviken. A conceptual model was initially created to describe the hydrological system in a simplified way with regards to the geology, hydrology and climate within the area. The model domain was delimited by topographical water divides and hydrological boundaries, and was thereafter divided into three horizontal layers based on the main materials that have been identified during investigations within the area: filling material, clay and till. In GMS, the model domain was divided into a 5x5 meter grid and its borders were assigned appropriate boundary conditions. By interpolating the three model layers from scatter point data of known geology, the conceptual model could be described mathematically within the software. To increase the reliability of the model, the hydraulic conductivities of the materials were then calibrated against observed hydraulic head in several groundwater monitoring wells in the area. After the calibration, the hydraulic conductivities of the filling material, clay and till were 2,1ˑ10-4 m/s, 5,7ˑ10-7 m/s and 3,9ˑ10-5 m/s respectively. A sensitivity analysis was then performed in order to examine how the values of hydraulic conductivity and groundwater recharge would affect the model results. Simulations with the calibrated model showed that the groundwater generally moves from the western parts of the area towards Pjältån and Loddbyviken in the north and east. However, it moves around the areas where the impermeable bedrock is close to the ground surface. Changes in the water level of Loddbyviken proved to have some effect on the amount of water in the system, but they did not entail a greater influence on the groundwater movement pathways in the area. The sensitivity analysis showed that the model was very sensitive regarding the groundwater recharge and the hydraulic conductivity for the till. A very low conductivity of clay turned out to lead to some modeling difficulties and the conductivity of the filling material showed to only have a small effect on the result.
6

Characterization of nutrient transport and transformations downstream of on-site wastewater disposal facilities

Jiang, Ying 29 August 2011 (has links)
The purpose of this project is to gain an improved understanding of the transformations that occur in the subsurface downstream of on-site wastewater disposal systems and septic systems. These systems are used widely throughout the United States to treat and discharge wastewater effluent. The approach involved the collection of samples from a septic research center in Cape Cod, MA, and analysis of these samples for nitrogen, phosphorus, dissolved oxygen, pH, alkalinity, suspended solids, metals, and other water quality parameters. Inverse modeling was used to compare samples collected upstream and downstream of subsurface “leaching” fields consisting of sand beds. This approach provided a basis to identify key reactions occurring in the subsurface downstream of the discharge. In addition, a reactive transport software package, based on the PHREEQC and Hydrus-1d models, was used to model the transport in these sand beds and identify possible reactions and changes in contaminant concentrations with depth. To understand the implications of the discharges, an additional field study was completed in an area where septic systems have impacts on surface waters. Samples collected from a stream provided an indication of the loads entering the stream as a result of septic system discharges. Combining the results from the modeling with the results of this field investigation provided an approach to estimate the transport of nutrients and other contaminants entering the surface waters from septic system discharges. The results provide a basis for understanding the impacts of septic systems on surface waters, and develop better approaches for reducing the impacts of these discharges.
7

Parallel Processing for Modeling Reactive Transport in Groundwater

Wright, Jennifer 26 May 2006 (has links)
Natural attenuation and biotransformation are processes that can potentially control the transport and enhance the remediation of contaminants in groundwater. It is necessary to develop computer simulations that not only model the physical transport (advection and dispersion) of contaminants, but that can also accurately depict chemical reactions and some of these more complex processes, in order to determine the type and extent of contaminant plumes and to analyze potential remediation strategies. Modeling these systems effectively is becoming possible with a growing understanding of the chemical and biological processes that occur in groundwater. However, more accurate and more involved models come with much higher memory and computational requirements. Parallel processing provides the computational resources needed to employ reactive transport simulations effectively and more efficiently. N2D-H2 is a FORTRAN code that simulates two-dimensional reactive solute transport in groundwater. More specifically, it simulates the biotransformation of nitrate into the end products of denitrification. A parallel version of the N2D-H2 code is developed using the Message-Passing Interface (MPI), a library of sequences and routines that can be called from FORTRAN programs. Using MPI to develop the parallel version of the code involves decomposing the computational domain among processors, defining the computational roles of each processor, and implementing the required communication between processors by using the message-passing procedures that allow the processors to exchange data. Several test problems are developed to analyze the performance of the parallel code. The test problems are used in the benchmarking procedure to demonstrate that the parallel code returns results identical to the sequential code. The CPU time required and the speedup achieved by running the simulation on parallel processors is presented for multiple test problems with varying physical processes and computational grid sizes. For a two-dimensional plume simulation of five solutes, with a finite difference grid of 490 nodes x 99 nodes, the total CPU time is decreased from 410 seconds on one processor to 220 seconds on two processors, and 75 seconds on ten processors. The speedup achieved gets closer to the ideal speedup as the problem size increases. Although the speedup observed with the parallel version of N2D-H2 is not 100% of the ideal speedup because of communication requirements, the parallel simulation demonstrates the benefits of parallel processing and the possibility of expansion that it provides for modeling reactive transport in groundwater. / Master of Science
8

An Integrated Approach of Analyzing Management Solutions for the Water Crisis in Azraq basin, Jordan

Alkhatib, Jafar 12 May 2017 (has links)
No description available.
9

Evaluating Alternative Hydraulic Solutions to Limit Nutrient Contamination of an Aquifer in Southern California

Perry, Jake Mendoza 01 April 2012 (has links)
Many small communities depend on groundwater sources for drinking water and they often use septic tanks for their sewer system needs. However, nitrates and other pollutants from septic systems can percolate to the aquifers and deteriorate quality of the groundwater, threatening the public health. This study has developed a groundwater model using Visual MODFLOW for an aquifer that is used as a water supply source for the cities of Beaumont and Cherry Valley, California. Septic systems are the suspected major source of nitrate contamination of the aquifer. The model has been developed to clarify the extent of interactions between nitrate pollutants, infiltration and percolation from a recently established series of artificial recharge ponds, groundwater recharge from natural sources, and pumping activities to meet local water uses. The primary objective of this study is to evaluate alternative hydraulic solutions that would limit the movement of the contaminants and minimize the risk of affecting the pumping wells. The study attempts to identify the best way to recharge the aquifer and influence movement of the nitrates so that polluted waters may have lower nitrate concentrations in the future, rather than allowed to encroach on critical production wells or led away from production wells to become a problem for future generations or neighboring areas. The data needed to build the model, including geological logs, precipitation, evapotranspiration, well locations, pumping schedules, water levels, and nitrate concentrations have been obtained from the Beaumont Cherry Valley Water District. The model has been calibrated to simulate the observed groundwater levels and the extent of pollution corresponding to the historical pumping rates, recharge rates and climate. The calibrated model has been used to evaluate alternative hydraulic solutions that would either localize the nitrate pollution thus limiting the impact on public welfare, or remove the nitrate pollution for potential treatment and remediation on the surface. The study results show that increased pumping of production wells or strategic placement of additional artificial recharge may reduce the concentrations of nitrate in the Beaumont Basin.
10

Modeling a controlled-sourced, multichemical plume undergoing natural attenuation

Martin, Caitlin January 2004 (has links)
Sampling of an emplaced creosote source installed below the water table at CFB Borden was conducted over a period of ten years, with over nine thousand samples taken from approximately 250 multilevel samplers. This extensive dataset was used in several attempts to model the multi-chemical plumes emanating from this emplaced source, and to further understand the chemical and biological processes affecting these plumes and their natural attenuation. An aerobic microcosm study of naphthalene, 1-methylnaphthalene and acenaphthene was conducted in order to determine the possibility of interactions between these three chemicals. All three chemicals degraded within the eight days of the study, and the degradation of naphthalene and 1-methylnaphthalene was not affected by the presence of any of the three chemicals studied. Acenaphthene degraded more quickly when naphthalene was present in the microcosm. The programs Visual MODFLOW and RT3D were used to model the transport and degradation of naphthalene at CFB Borden. Both a first order rate reaction module and a multiple electron acceptor reaction module were used, and contaminant mass was introduced to the model through a fence of observed concentrations. Good results were found at early time with the multiple electron acceptor reaction package, however at late time the model did not match to observations. The program BIONAPL/3D was used in a similar attempt to model the transport and degradation of naphthalene. Naphthalene mass was introduced to the model through a fence of observed concentrations, and multiple electron acceptors were used to degrade this chemical. Results were good at early time, but at late time the model did not match observations. BIONAPL was then used to simulate the dissolution of the original source NAPL. Several chemicals of interest were examined: naphthalene, m-xylene, 1-methylnaphthalene and acenaphthene. Naphthalene and m-xylene dissolved from the source at rates similar to observations, however the dissolution of 1-methylnaphthalene and acenaphthene was not as well modeled. As with the Visual MODFLOW model, the BIONAPL model which best matched observations generally worked well at early times, but did not at late times. The models were not able to successfully simulate many processes that occur in the field, such as chemical and biological interactions and NAPL source dissolution. Mismatches between the models and observations are likely due to these reasons. It may be that we do not fully understand these processes, so we are unable to model them.

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