<p> Early thermal breakthrough is an issue of concern in the geothermal industry, especially with regard to engineered geothermal systems (EGS). Determination of the specific surface area (SSA) of the fluid/rock interface in an EGS is vital to predicting early thermal breakthrough. An approach to this problem involving the application of tracers with different sorption properties (lithium, bromide, and deuterium) is presented. Upon injection into a reservoir, these tracers react along the fluid/rock interface to varying degrees. The resulting breakthrough separation at the extraction well can be used to derive SSA by applying a modified form of the advection-dispersion equation. For proof of concept, field tests were conducted in a sandstone bedding-plane fracture near Chazy, New York. Results showed minimal breakthrough separation, indicating insufficient sweep of the fracture area, and that lithium was not an ideal tracer in this medium. However, a relative measure of SSA can still be derived. </p>

<p> Karst carbonate aquifers are traditionally difficult to model due to extreme permeability heterogeneities and non-Darcian flow. New modeling techniques and test applications are needed to improve simulation capabilities for these complex groundwater systems. This study evaluates the coupled continuum pipe-flow framework for modeling groundwater flow in the Madison aquifer near Rapid City, South Dakota. The Madison carbonate formation is an important source of groundwater underlying Rapid City. An existing equivalent porous medium (EPM) groundwater model of the Madison aquifer was modified to include pipe networks representing conduits. In the EPM model, karstified portions of the aquifer are modeled using high hydraulic conductivity zones. This study hypothesized that the inclusion of conduits would allow for a simpler hydraulic conductivity distribution and would improve modeled fits to available data from a 10-year monitoring period. Conduit networks were iteratively fit into the model based upon available environmental and dye tracer test data that approximated major karst pathways. Transient simulation results were evaluated using observation well hydraulic heads and estimated springflow data. In a comparison to the EPM model, the new modeling results show an improved fit to the majority of observation well targets, and negligible impact to springflow data. The flow dynamics of the aquifer model were significantly altered, with the conduit networks acting as gaining or losing subsurface features, behaving as regional sinks during dry periods and flowpath heterogeneities during wet periods. The results of this study demonstrate that the coupled continuum pipe-flow modeling method is viable for use within large regional aquifer models.</p>

<p> Determining the hydraulic properties of aquifer and aquitards (K,T,and S) is very important in hydrogeologic studies. These parameters can be identified by methods such as laboratory permeability and borehole hydraulic response test. Because these approaches are sometimes costly, involving drilling test holes, and often may not be feasible, numerical modeling approaches can be considered as alternatives. In the following study, numerical modeling is applied to simulate groundwater flow system to determine the hydraulic properties of a weathered/fractured zone in a valley located within the Appalachian Plateau Geomorphic Province. The Appalachian Plateau is characterized by relatively flat-laying but intensely eroded bedrock, comprising cyclical sequences of Pennsylvanian age sedimentary bedrock dominated by sandstone, siltstone, shale, coal, claystone, and occasionally limestone. Fractured/weathered sandstone is potentially the main bedrock groundwater transmitting formation. The extent of fractures is from the ground surface to about 120-150 ft (or roughly 30-40m) under the ground surface. The main groundwater flow occurs from within the intergranular pore space through fractures and along bedding planes of the bedrock. </p><p> The water level at a perennial stream in the valley can be considered as the phreatic ground-water level. Therefore, the elevation points along this stream may serve as model calibration points. Because the outflow from the valley is almost entirely via the creek, and creek water represents the groundwater level all along the valley, the model is calibrated and verified by the creek water elevations and the amount of water discharging through the valley. The site- specific hydrogeologic interpretation and evaluation technique presented in this study may be very well applicable to the significant portions of the Allegheny Plateau with similar geomorphologic, tectonic and lithologic characteristics.</p><p> </p>

Thesis (Ph. D. - Geology)--University of Arizona, 1969. / Part of folded illustrative matter in pocket. Includes bibliographical references (leaves 100-103).

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7197. Adviser: Stephen Marshak. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

A lineament analysis for Georgetown, Maine, a 44 km$\sp2$ island community situated on the central Maine coast, was performed to evaluate the relationship between mapped lineaments and (1) outcrop fractures, (2) well productivity (35 wells), and (3) groundwater quality determined from a sample of 87 existing bedrock wells. Lineaments were drawn by three observers using two scales of imagery (SLAR and a 1:80,000 Aerial Photograph). Rigorous reproducibility testing indicates that the ability of individual observers to reproduce lineaments at the same geographic location is low; more than 55% of all lineaments mapped by any observer were not reproducible. This casts doubt as to how many lineaments may be considered real features. In addition, when azimuthal sets of near-vertical outcrop fractures are compared with reproducible lineament domains of similar azimuth on a regional basis, distinct areas of overlap are defined across the island. The extent of this overlap is not uniform. Some lineament domains (165$\sp\circ$) exhibit no correlation with fracture fabric whereas other lineament domains (120$\sp\circ$) only show a correlation with fracture fabric in a very limited geographic area. In regard to well productivity, wells located "on" lineaments, specifically those lineaments showing a geographic correlation with similar-trending fracture domains, are generally more productive than non-lineament wells. If the same analysis is repeated, but is performed without considering whether or not the lineaments used in the analysis are geographically correlative with fracture domains, no differences are observed between the productivities of lineament and non-lineament wells. However, in this study, other geologic factors exhibit strong influences on high productivity in bedrock wells. Bedrock type (amphibolite) is the dominant and only statistically significant influence on well productivity followed by depth to the water table (shallow depths), proximity to lineaments (specifically those that correlate geographically with outcrop fractures), topographic position (flatter hydraulic gradients), and proximity to surface water bodies, in order of decreasing importance. Groundwater chemistry is controlled primarily by bedrock type, topographic setting, structural position, and overburden type and thickness. The chemical character of groundwater sampled from bedrock wells is generally not influenced by the proximity of a well to a lineament.

Many studies have focused on hydrological and geochemical fluxes from land to the ocean via groundwater discharge, however few have assessed groundwater flow in deltaic settings. Hydrological budgets indicate that 1,000 to 5,000 m3s-1 of water flow from the Mississippi River (MR) to its delta (MRD) via subterranean pathways, however the spatial and geological controls on these processes are less known. This study suggests that deltaic lithofacies of paleoenvironments related to the delta cycle allow for groundwater to discharge out of the MR main channel and into the MRD through organic sediment-rich and silt-sand overbank and mouth bar facies. This study employs geophysical data, including chirp sonar subbottom profiling and continuous resistivity profiling (CRP), to detect the location of these sediments in Barataria Bay, a coastal bay located in the MRD. Chirp data indicate paleochannel features in the MRD, whereas CRP data indicate freshwater seepage into MRD embayments during high river stage events. Analyses of bulk properties of sediment cores are used to characterize delta facies sediments and determine variability in hydraulic conductivity values, which range from 10-7 to 10-2 ms-1. These geophysical and sediment core data show the potential for groundwater flux through deltaic sediments, and will contextualize geochemical tracer data collected by project collaborators. Results indicate that groundwater discharge in the MRD is directly controlled by the geological constraints of the delta region. These results illustrate the potential for substantial groundwater fluxes in other large river deltas, and present implications for urban and coastal infrastructure planning, as many large global deltas sustain significant populations. / 1 / Alexander M Breaux

<p> Recharge areas for most springs are rarely known because they can be sourced from proximal, shallow, atmospheric sources or long-travelled, deep, regional aquifers and alteration along the flow path is common. Stable isotopic (¹⁸O and ²H) geochemistry of springs water can provide indications of relative flow path distance. Locally sourced springs generally have an isotopic signature similar to the isotopic values of local precipitation for that region and elevation. Springs with a different isotopic composition than local meteoric inputs likely have non-local recharge, representing a regional source. Exceptions to this rule include springs in karst terrain, geothermal locations, or travertine-rich groundwater systems, where other physical or geochemical processes influence the isotopic signature of the water. In this study, we tested local vs. regional sourcing using springs isotopic data from regional studies across Western North America in Arizona, Nevada, and Alberta. These regional study sites included the Basin and Range, Transition Zone, Colorado Plateau, Cordillera, Interior Plains physiographic regions, and lowland to montane aquifers. The combination of location-specific physical data with stable isotopic groundwater data provides an effective method for flow path determination at springs with similar flow and chemistry. Springs from Arizona were found to be a mix of regional and local recharge, those from Nevada were locally sourced, and Alberta's springs are generally sourced from regional flow systems. </p><p> Springs provide a truly unique ecosystem where groundwater first daylights, mixes with surface waters, and both plants and animals find refuge. Variability of springs type (the springs geomorphic properties) can have profound effects on all aspects of a groundwater spring. Water chemistry may exert significant changes on vegetation, which in turn modify the springs ecology. Changes in vegetation composition and density can also change erosion rates and channel morphology, thereby altering geomorphology. Analyses of data from southern Nevada and Alberta, Canada housed in an extensive springs database of western North America were interpreted to determine the interconnectedness of geochemistry, geomorphology, and vegetation cover. Using various statistical techniques, the opposite variables were significant in the two field areas. In the Spring Mountains the highest elevation clusters had the highest plant species diversity and the fewest spheres of discharge. In Alberta the clusters with average elevation, neither highest nor lowest, were the groups with the highest plant species diversity and most variability in geomorphic surface types.</p>

<p> This study investigates the potential for hydrothermal alteration and circulation in lava domes using combined analytical, remote sensing and numerical modeling approaches. This has been accomplished in three parts: <i>1) </i> A comprehensive field, geochemical and remote sensing investigation was undertaken of the hydrothermal system in the Santiaguito lava dome complex in Guatemala. The Santiaguito domes were found to contain mainly hydrous silica alteration, which is unlikely to weaken dome rock, but the summit of Santa Maria was found to contain pervasive argillic alteration (clay minerals), which do pose more of a collapse-related hazard. These results were confirmed by hot spring geochemistry which indicated that water in the domes was responsible for some rock dissolution but had a residence time too short to allow for secondary mineralization. <i>2)</i> A finite element numerical modeling approach was developed which was designed to simulate the percolation of meteoric water in two dome geometries (crater-confined and 'perched'), and the results were compared to the surface expression of hydrothermal systems on existing lava domes. In both cases, we concluded that simulated domes which lacked a high-temperature (magmatic) heat source could not develop a convecting hydrothermal system and were dominated by gravitational water flow. In these low-temperature simulations, warm springs (warmer high fluid fluxes) were produced at the base of the dome talus and cool springs were dispersed lower down the slope/substrate; fumaroles (high vapor fluxes) were confined to the dome summits. Comparison with existing dome cross sections indicates that the simulations were accurate in predicting fumarole locations and somewhat accurate at predicting spring locations, suggesting that springs may be subject to permeability contrasts created by more complicated structural features than were simulated in this study. <i>3)</i> The results of the numerical modeling were used to calculate alteration potential in the simulated domes, indicating the most likely areas where alteration processes might either reduce the strength of a dome or reduce permeability that could contribute to internal pressurization. Rock alteration potential in low-temperature lava domes was found to be controlled by material permeability and the presence or absence of a sustained heat source driving hydrothermal circulation. High RAI values were preserved longer in low-permeability domes, but were more strongly developed in domes with higher permeabilities. Potential for mineral dissolution was highest at the base of the dome core, while the potential for mineral precipitation is highest at the dome core-talus interface. If precipitated minerals are impermeable, the dome core/talus interface would be a likely location for accumulation of gases and initiation of gas-pressurization-related collapse; if alteration is depositing weak (i.e. clay) minerals in this area, the dome core/talus interface might be a candidate for collapses occurring as the result of alteration processes. </p><p> The results of this study are all geared toward answering two broad questions: <i> Where are hydrothermal alteration processes likely to occur or be focused within lava domes?</i> and <i>What effect could these processes have on dome stability?</i> In the specific case of the Santiaguito dome complex, the combination of a quickly-recharged, low-temperature hydrothermal system in the inactive domes actually indicated a low possibility of collapse related to alteration minerals. This result was reinforced by the results of the numerical modeling, which indicated that domes are unlikely to develop sustained hydrothermal convection without the presence of a significant (magmatic) heat source and&mdash;in the case of Santiaguito&mdash;are likely to produce more hydrous silica alteration minerals when they also lack a source of acidic gases. Models of alteration potential do detail, however, that both shallow and deep dome collapses are still a possibility with a low-temperature hydrothermal system, given either a) a source of acidic gases to drive the formation of clay minerals (which are most likely to be deposited at the core/talus interface of a dome, or b) enough deposition of silica minerals in pore spaces to lower permeability in dome rock and promote internal gas pressurization. The results of this study are not limited to lava domes, as the volcanic edifices on which they rest are composed of the same materials that comprise lava domes and are therefore susceptible to the same hydrothermal processes. Further simulations of both lava domes and their associated edifices, including mineral species models, could help constrain under what conditions a lava dome or volcano is likely to develop areas of weak mineral precipitates (such as clay minerals) which could provide sites for collapse, or develop an impermeable cap of silicate minerals which could trap rising vapor and contribute to the pressurization of the edifice in question (which can in turn lead to collapse).</p>

<p> Rock scour downstream of dam foundations and spillways has become a significant dam safety concern in recent years. As design flood estimates increase and older infrastructure is expected to pass larger amounts of water, downstream river beds and plunge pools are subjected to progressively greater stream power from rapidly flowing water. A need exists to quantify the erosive capacity of the flowing water and the erodibility of earth materials to evaluate potential scour in these susceptible areas. Annandale's Erodibility Index Method, widely considered a state of the art scour prediction method, offers an approach to quantify scour depth by comparing the erosive capacity of flowing water and the ability of rock to resist it. </p><p> This study assesses the accuracy of Annandale's Erodibility Index Method for estimating rock scour depth in plunge pools. The success by which the method may be implemented is dependent on the accuracy of methods to quantify the rate of energy dissipation of plunging jets (applied stream power) and the ability to estimate the capacity of rock to resist the power of the flowing water. The stream power of plunging jets is quantified by making use of published research, while the ability of rock to resist scour is computed using a geo-mechanical index, known as the Erodibility Index. </p><p> The Erodibility Index that was used to estimate the scour resistance of the various stratigraphic layers downstream of four BC Hydro dam spillways located in British Columbia, Canada relies on in-situ rock parameters consisting of UCS strength values, RQD values, joint spacing, aperture, alteration, roughness, and orientation. The jet stream power was calculated using continuous daily discharge records and spillway geometries at each of the dams, and published research on stream power quantification. The spillway types included one long spillway chute with a free overfall and a number of flip bucket-type energy dissipaters. </p><p> Comparison between the numerically generated scour profiles and a series of plunge pool surveys at each of the dams provided a means of determining accuracy. Scour depths and the distances between the end of the spillways and the points of maximum scour were matched. The study revealed that correlations between calculated and observed scour profiles improved with the quality of geologic information and with the certainty by which the stream power of jets and their decay could be quantified. </p><p> The geologic information at two of the dams, Revelstoke and Seven Mile Dams, was incomplete and resulted in a generalized characterization of the scour resistance of the plunge pool rock. At these dams it was not possible to spatially characterize changes in scour resistance of the rock in the plunge pool. The geologic information at Peace Canyon and W.A.C. Bennett Dams was more informative and allowed quantification of the spatial distribution of plunge pool scour resistance in each case. </p><p> The research further identified that jet theory associated with flip buckets provides good estimates of stream power and its decay, but that hydraulic theory used to quantify the energy dissipation in long spillway chutes may be incomplete at this point in time. The combined inadequacy of geologic data and the insufficiency of hydraulic theory related to long spillway chutes resulted in the comparison between surveyed and calculated scour depths at Revelstoke Dam being particularly poor. Contrasting this result, it was found that better understanding of flip bucket hydraulics and more informative geologic information resulted in very good correlations between calculated and surveyed scour profiles at Peace Canyon and W.A.C. Bennett Dams. The comparison provided more pleasing results at Seven Mile Dam than at Revelstoke Dam, in spite of the relatively poor geologic information in the plunge pool area of Seven Mile Dam. The improved correlation at Seven Mile Dam may be attributed to the fact that it has a flip bucket spillway, which resulted in better quantification of jet stream power and its decay. </p><p> In summary the analysis results indicate a strong correlation between surveyed and modeled plunge pool depth and invert location at dam sites where both the hydraulics and geology are well understood. It is concluded from this research that Annandale's Erodibility Index Method is an accurate method for estimating plunge pool depth when geologic information is available and spillway and plunge pool hydraulics are well-understood. A lack of information or understanding of the spatial distribution of materials generally results in less accurate predictions. </p><p> Although this research project was not directed towards determining the rate of scour of rock, a good correlation was found between cumulative energy (the product of stream power and duration) and scour depth. This preliminary result provides encouragement for future research into using the Erodibility Index Method to quantify the rate of scour in rock. </p><p> The analysis would benefit from more robust rock parameter datasets that would allow for the inclusion of a Monte Carlo simulation within the model. Additionally, a larger dataset of dams including those with various spillway structure types and geologic environments would be valuable moving forward. </p>