This dissertation is composed of three parts of major contributions: In Chapter II, we developed a new conceptual model and derived a new semi-analytical model for flow to a horizontal well beneath a water reservoir. Instead of treating the leakage from aquitard as a source term inside the aquifer which is called Hantush’s assumption (1964), we linked flows in aquitard and aquifer by the idea of continuity of flux and drawdown. The result in this chapter is compared with that of Zhan and Park in 2003 which Hantush’s assumption is adopted at various hydraulic and well configurations. It shows that Hantush’s assumption becomes inaccurate in regions where vertical velocity components are significant. In Chapter III, we deal with the interaction of an aquifer with two parallel surface water bodies such as two streams or canals. In this chapter, new closed-form analytical and semi-analytical solutions are acquired for the pumping induced dynamic interaction between two streams and ground water for two different cases. In the first case, the sediment layers separating the streams from the aquifer ground water do not exist. In the second case, the two low permeable layers are considered. The effect of aquitard and water right competition is addressed in this chapter. This model can be used for interpreting and deriving hydrologic parameters of aquitard and aquifer when pumping occurs between two channels. It can also be used to predict stream depletion which is essential for water management and ecology conservation. In Chapter IV, we investigated the three dimensional upconing due to a finite-length of horizontal well and its critical conditions. The results are compared with those of vertical wells. The critical condition which includes the critical rise and the critical time at a certain pumping rate depends on the well length, the initial interface location, the well location, and the pumping rate. Our results show that horizontal well might be a better tool for coastal groundwater resources development. In real field applications, installing long wells as shallow as possible is always desirable for sustaining long periods of pumping with significant rates.

This dissertation is composed of three parts of major contributions: In Chapter II, we developed a new conceptual model and derived a new semi-analytical model for flow to a horizontal well beneath a water reservoir. Instead of treating the leakage from aquitard as a source term inside the aquifer which is called Hantush’s assumption (1964), we linked flows in aquitard and aquifer by the idea of continuity of flux and drawdown. The result in this chapter is compared with that of Zhan and Park in 2003 which Hantush’s assumption is adopted at various hydraulic and well configurations. It shows that Hantush’s assumption becomes inaccurate in regions where vertical velocity components are significant. In Chapter III, we deal with the interaction of an aquifer with two parallel surface water bodies such as two streams or canals. In this chapter, new closed-form analytical and semi-analytical solutions are acquired for the pumping induced dynamic interaction between two streams and ground water for two different cases. In the first case, the sediment layers separating the streams from the aquifer ground water do not exist. In the second case, the two low permeable layers are considered. The effect of aquitard and water right competition is addressed in this chapter. This model can be used for interpreting and deriving hydrologic parameters of aquitard and aquifer when pumping occurs between two channels. It can also be used to predict stream depletion which is essential for water management and ecology conservation. In Chapter IV, we investigated the three dimensional upconing due to a finite-length of horizontal well and its critical conditions. The results are compared with those of vertical wells. The critical condition which includes the critical rise and the critical time at a certain pumping rate depends on the well length, the initial interface location, the well location, and the pumping rate. Our results show that horizontal well might be a better tool for coastal groundwater resources development. In real field applications, installing long wells as shallow as possible is always desirable for sustaining long periods of pumping with significant rates.

Secondary structures (e.g., fractures, sand lenses, kimberlite intrusions) can compromise the ability of clay-rich bedrock aquitards to protect underlying aquifers from near-surface contamination. To date, the effects of secondary structures on water migration and solute transport in these deposits have been poorly characterized. This study characterized the water migration and solute transport mechanisms at both a geologically simple and a geologically complex late-Cretaceous shale aquitard, with the field sites located 5 km apart in central Saskatchewan, Canada. The geotechnical properties and hydrogeologic properties of the complex aquitard were altered by kimberlite volcanism and subsequent hydrothermal alteration during its deposition (99 to 112 Ma BP). High-resolution, 1-D vertical profiles of conservative δ2H and Cl were collected from both sites (203 and 353 m deep, respectively) to define the vertical solute transport mechanisms. The shape of the 1-D tracer profiles and associated solute transport modeling from the geologically simple site suggest diffusion is the dominant transport mechanism through the entire thickness of the Lower Colorado shale aquitard (330 to 246 m above sea level, asl). Similarly, profiles through the complex, fractured, Cretaceous shale and associated modeling suggest diffusion is the dominant transport mechanism through the entire profile despite the presence of fractures; however, hydrothermal alteration during cooling of the kimberlite volcaniclastic material reduce the effective porosity (ne) of the kimberlite material from 40% to 1-5%. Results also suggest that, despite kimberlite emplacement in the study area, water migration and solute transport in the overlying and underlying Cretaceous shale may be unaffected by kimberlite volcanism and associated fracturing and alteration.

This dissertation is composed of five chapters and three major contributions are presented in Chapter II, III and IV. Chapter I provided a review of studies on solute transport in aquifer-aquitard system. If the aquitard is considered, two categories of methods address the diffusive flux between the aquifer and aquitard: the old method treats the diffusive flux as a volumetric source in the governing equation of the solute transport in the aquifer; the new method treats the aquifer-aquitard boundary as a strict physical boundary with the requirement of continuity of solute concentration and the vertical flux. The new method is adopted throughout this study. In Chapter II, a review of numerical techniques on Inverse Laplace Transform is provided. By careful comparison between several popular algorithms, the multiple precision Stehfest algorithm is chosen as the method to inverse out solutions on solute transport in Laplace domain throughout this dissertation. In Chapter III, solutions were obtained for two dimensional solute transport in an aquifer-aquitard system with a divergent radial flow field, which can treat different types of solute input function and advection, longitudinal and transverse dispersion in the aquifer, vertical diffusion in the aquitard, retardation and radioactive decay in the aquifer and aquitard are taken into account. Mass exchange via diffusion between the aquifer and aquitard are investigated. The effects of hydrologic properties of the aquitard on solute transport are analyzed. Comparisons were made between the results from this study and those from previous studies. The diffusion along the aquifer-aquitard boundary was treated as a volumetric source term, and proved these solutions yield more accurate solute concentration, while those from previous studies tend to overestimate solute concentration in the aquitard, and underestimate the concentration in the aquifer. In Chapter IV, solutions were derived for the transport of radioactive isotopes in an aquifer-aquitard system with regional flow field. This study focused on the effects of different solute transport processes on the results of groundwater age dating using radiometric techniques. Chapter V summarized the remaining problems in this study and directions for future researches.

Groundwater conditions beneath 11 hectares property owned by HydroOne near the southeastern edge of the Oak Ridges Moraine were assessed for contamination susceptibility using groundwater and geological information from HydroOne monitoring on-site and within one kilometre. Geological information was obtained from preexisting well records and a deep cored hole through dense glacial deposits (Newmarket Till) and through two deep regional sand aquifers (Thorncliffe and Scarborough Aquifers) into shale at 130 mbgs. The multiple data types included water levels, Tritium-Helium groundwater dating, oxygen-18 and deuterium, and major and minor ions. The water table is close to surface (<3m) and wells above 22 m depth in the highly active shallow zone show chemicals and Coliform Bacteria from human activities including roads, septics and agriculture. Shallow groundwater flows downward towards the Thorncliffe aquifer; the bottom of this most active zone is unknown due to insufficient data from deeper wells. Two private wells (100 mbgs) thought to be in the Thorncliffe aquifer contain constituents indicative of human influence. Seven of eight homeowner wells show tritium from nuclear power stations, one at detection limit. Three hypotheses are proposed to explain the susceptibility of wells in the Thorncliffe Aquifer to contamination: 1) the Newmarket aquitard is contains preferential pathways due to fractures connected to sand layers allowing deep penetration of contamination, 2) recharge can occur directly into the Thorncliffe aquifer in areas where Newmarket Till is non-existent, and 3) wells have faulty construction allowing short-circuiting to depth of contaminated shallow water down and along well casings. Based on the current data preferential pathways through the Newmarket is the most plausible hypothesis. However, additional work to define groundwater flow paths both on and off-site as well as additional geochemical and isotopic analyses from existing and new deep wells is needed to better determine risk to residential wells. / Thesis / Master of Science (MSc) / A groundwater study was conducted in an eight square kilometre area at the southeast edge of the Oak Ridges Moraine near Oshawa, ON. It included: geology from a 130m hole through overburden (including Newmarket Till) to bedrock, groundwater age determinations and water chemistry obtained by Hydro One from 16 monitoring wells on HydroOne property (11 hectares) and 25 nearby homeowner wells, most less than 22m deep. Wells above 22m show salt and other constituents from roads, septics or agriculture and show young groundwater age. Two deep wells (100m) in the Thorncliffe Aquifer beneath the Newmarket Till also show these chemicals; one of them sampled for tritium-helium showed young age, as do some intermediate -depth wells. The pathways for young water migrating so deep are undetermined.

Diffusion dominated systems, including naturally occurring aquitards and engineered barrier systems, are important components for long-term waste containment. Diffusive transport can be quantified using the effective coefficient of diffusion (De) and the effective porosity (ne). These are empirical parameters that are commonly measured in a laboratory setting. The purpose of this research was to develop a field-based technique to perform <i>in situ</i> measurement of diffusive transport rates. Results from this measurement technique were evaluated by comparison with the results of conventional laboratory testing and back-analysis of a previously determined large-scale field diffusion profile.<p> <i>In situ</i> diffusion testing was performed on two wells completed in diffusion-dominated zone of a till aquitard. Laboratory diffusion cell tests were conducted on core samples obtained from the screened zones of the diffusion wells. Diffusion testing was completed using conservative isotopes of water as tracers.<p>A finite element model was used to back-analyze results of laboratory and field experiments to determine the De values that best describe each system. Comparison of the field results with the laboratory results obtained from this study as well as previous studies indicate the field system is a useful method for measurement of De.<p>Back-analysis of a previously determined large-scale field deuterium profile for this aquitard showed very precise measurement of De is not required for estimation of contaminant transport in thick till aquitard systems. More accurate measurement may be more useful for barrier systems such as clay liners or slurry walls, where the characteristics of the diffusion-dominated zone are easier to define and the transport path is shorter relative to the transport time.

Diffusion dominated systems, including naturally occurring aquitards and engineered barrier systems, are important components for long-term waste containment. Diffusive transport can be quantified using the effective coefficient of diffusion (De) and the effective porosity (ne). These are empirical parameters that are commonly measured in a laboratory setting. The purpose of this research was to develop a field-based technique to perform <i>in situ</i> measurement of diffusive transport rates. Results from this measurement technique were evaluated by comparison with the results of conventional laboratory testing and back-analysis of a previously determined large-scale field diffusion profile.<p> <i>In situ</i> diffusion testing was performed on two wells completed in diffusion-dominated zone of a till aquitard. Laboratory diffusion cell tests were conducted on core samples obtained from the screened zones of the diffusion wells. Diffusion testing was completed using conservative isotopes of water as tracers.<p>A finite element model was used to back-analyze results of laboratory and field experiments to determine the De values that best describe each system. Comparison of the field results with the laboratory results obtained from this study as well as previous studies indicate the field system is a useful method for measurement of De.<p>Back-analysis of a previously determined large-scale field deuterium profile for this aquitard showed very precise measurement of De is not required for estimation of contaminant transport in thick till aquitard systems. More accurate measurement may be more useful for barrier systems such as clay liners or slurry walls, where the characteristics of the diffusion-dominated zone are easier to define and the transport path is shorter relative to the transport time.

Delineating the extent of brine contamination in shallow groundwater systems using piezometers is costly and does not provide adequate data resolution. Direct-push (D-P) electrical conductivity (EC) profiling enables rapid in situ measurements of bulk soil EC (ECa) at the cm scale. Previous studies using D-P EC profiling to detect contaminant plumes have solely relied on ECa measurements, and where attempts were made to isolate pore-water salinity variations from changes in ECa they were accomplished using simple linear methods. In this study D-P EC profiling was used to define groundwater salinity distributions using an established soil conductance model and estimate the timing of groundwater contamination at a long-term potash mine in south-central Saskatchewan, Canada. The site was dominated by fine-grained postglacial and glacial sediments with known Na-K-Cl brine impacts resulting from mining activities. Coreholes (n=22) were drilled to 7.6-12.2 m below ground (mbg) to obtain continuous cores for detailed geologic descriptions and measurements of index parameters (n=522) below the water table. Pore-water EC (ECw) and Cl- results from squeezed core samples (n=142) at 12 locations were compared to ECa measurements collected using a D-P probe adjacent to each corehole. Measured ECw and pore-water Cl- results ranged from 1.94-55.1 mS/cm and 87-20,700 mg/L, respectively. In situ D-P EC values from logs collected adjacent to all 22 coreholes ranged from 2-8 mS/cm within the oxidized zone (5-6 mbg) and decreased to background values of 0.3-2 mS/cm within the underlying unoxidized zone. Significant linear ECa–ECw regressions established for four lithological groups (r2=0.78-0.95) were used with porosity and dry density measurements to generate high-resolution depth profiles of ECw from D-P EC measurements. A significant linear ECw–Cl regression (r2=0.92) further enabled the generation of pore-water Cldepth profiles from ECw predictions. Observed 1D vertical profiles of Cl-, ECw, and ECa at three locations were modeled. Results suggested solute transport can be described as diffusion-dominated below depths of 3-5 mbg and that groundwater contamination began shortly after the onset of mining. Based on the results attained, this method can generate high-resolution depth profiles of pore-water salinity that can be used to define the lateral and vertical extent of brine contamination, dominant solute transport mechanisms, and timing of groundwater contamination.

Made available in DSpace on 2014-06-12T18:03:45Z (GMT). No. of bitstreams: 2 arquivo2597_1.pdf: 10436181 bytes, checksum: b4e4d682188b270e4a924aa344cd3e31 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2011 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A região de estudo fica localizada entre as cidades de Mossoró, no Rio Grande do Norte e Limoeiro do Norte, no Ceará. Geologicamente a Chapada do Apodi está inserida na Plataforma Aracati e abrange o Grupo Apodi. O sistema aquífero Apodi é composto do topo para a base, pelo aquífero livre cársticofissural Jandaíra, pelo aquitard Quebradas e o aquífero semi-confinado Açu. O levantamento geológico-estrutural determinou à evolução tectono-estrutural no cenário hidrogeológico regional, em especial quanto ao desenvolvimento das feições cársticas da Formação Jandaíra. Fraturas de extensão, com direção NW-SE e NE-SW, são as principais estruturas que governam a recarga do aquífero Jandaíra e a formação das cavernas, sumidouros e dolinas. Feições estruturais observadas ao longo da cuesta oeste da Chapada do Apodi envolvem falhas distensionais de direção NNW, com mergulhos de alto ângulo. Estudos gravimétricos determinaram a distribuição espacial do sistema aquífero Apodi, estimando os pacotes sedimentares para avaliação das reservas disponíveis de água subterrânea. A integração da modelagem gravimétrica 2D e 3D apresentou o contorno superior do embasamento com mergulho suave no sentido norte e nordeste. A profundidade máxima de 930 m foi atingida no depocentro de Baraúna, mostrando tendência distensiva e de afinamento crustal. A região leste e oeste da área ficaram caracterizadas pelo controle de falhas normais e o conseqüente desenvolvimento de horsts e grabens formando janelas de sedimentação com até 730 m de profundidade. A porção sul é marcada por forte anomalia gravimétrica positiva de direção E-W, explicada pela ocorrência de rochas vulcânicas, possivelmente associadas ao evento magmático Rio Ceará Mirim. A eletrorresistividade determinou a compartimentação estrutural da Chapada do Apodi, em quatro patameres: Alto de Lagoinha (cotas variando entre -330 e -200 metros), Plataforma de Baraúna (cotas variando de -400 a - 550 metros), Baixo da MAISA (cotas atingem -700 metros) e Graben de Boa Vista (cotas atingem - 900 metros), esses blocos estão condicionados pelo sistema de falhamento de Tiradentes, Falha da MAISA e Juremal. Com os dados obtidos neste trabalho foi visto que a compartimentação tectônica da Chapada do Apodi é controlada por falhas extensionais associadas ao embasamento, formando depressões que são de fundamental importância para acúmulo de água subterrânea

The Newmarket Till is a regional aquitard in southern Ontario that overlies the Illinoian to Middle Wisconsinan Lower Sediments and is overlain by the Oak Ridges Moraine (ORM). Geological investigations have mapped the distribution of the till and it is understood that erosional channels, subsequently infilled with fluvial material, breach the till and may create enhanced hydraulic connection between overlying and underlying aquifers. However, little is known about the protective capability of the Newmarket Till where it is intact. This study used natural tracers to assess the extent of transport in the aquitard-aquifer system. Stable isotopes of water (δ18O and δ2H) showed a depletion trend versus depth. In the Newmarket Till most of the samples had isotope ratios similar to meteoric water data from the nearest location (Egbert, ON). The depleted values of δ18O in the Thorncliffe Formation suggest a remnant signature of early-Holocene precipitation (-16‰ at the depth of 60 m). Elevated levels of NO3- and Cl- were detected near the surface and because of the low permeability aquitard (Newmarket Till), they could not migrate to depth. Total extractable ammonium concentrations are ranging from 4.09 ppm from near the surface to 60 ppm in the lowest part of the Newmarket and then gradually increase to 514 ppm in the bottom of the Thorncliffe Formation. The combination of high NH4+ values and organic carbon content in the Thorncliffe Formation suggests a natural source from mineralization of organic N. The fractionation which happened between δ15Nsediment and δ15N-NH4 may have three explanations: (1) lighter isotopes diffuse faster than heavier ones, so the higher rate of diffusion can cause fractionation; (2) heavier isotopes partition to exchange sites, causing fractionation along the transport pathway; (3) dissociation of NH4+ to NH3 under anaerobic condition. Positive values for δ13C in groundwater in the Thorncliffe Formation are likely due to i) a contribution of carbonate mineral dissolution, and ii) methanogenesis - the Archea favor the lighter isotope of C (12C). Methanogenesis, therefore, enriches the δ13C-DIC was enriched; however, the δ13C in dissolved organic carbon (DOC) is depleted. These geochemical characteristics demonstrate a long residence time for the porewater in the system and indicate that the Newmarket till inhibits recharge of recent precipitation, thereby providing protection to the underlying aquifers from surface-derived contaminants.