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Collection Description

Collection of student theses and dissertations from as early as 1939, but mainly from 2010 to present.

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A study of thermal waters in Valle Trinidad, Baja California, Mexico
Well and spring waters were collected and analyzed in Valle Trinidad in order to assess a relationship between the geology and valley hot water system. The chemistry of the thermal waters is distinct from that of the normal groundwater system such that the extent of the thermal component was determined to be limited in the alluvium. The hot waters are restricted below a clay layer or series of layers functioning as a semipermeable membrane that prevents interaction of the water on either side of this barrier. The presence of the thermal water can be recognized only where it penetrates into the alluvium above the clay layer. The thermal water emanates at the hot spring, S1, where the clay seam outcrops at the surface. The chemistry identifies a thermal component at the town spring, S3, probably percolating up along a permeable normal fault-associated zone. The well data also support a north- south fault through well locations PW10, PW11, PW12, which serves as a zone of leakage for the thermal waters. Geothermometers were utilized from the geochemical data and indicate the reservoir temperature for the thermal water to be 90° to 103°C. The extent of the thermal water below the clay cannot be predicted. The remainder of the valley groundwater system follows a normal groundwater circulation pattern in the alluvium flowing from the perimeter recharge areas to the center of the valley, yielding an increase in the total dissolved solids and the major ions, Cl and SO4 , in the central areas., San Diego State University
A transient method of soil vapor extraction testing involving vertical air leakage
Soil vapor extraction (SVE) is a useful remedial technique to remove volatile contaminants from unsaturated soil. In order to design an effective SVE system, the controlling air flow parameters must be described. Prior work has suggested that vapor flow at contaminated sites is generally confined between overlying concrete and asphalt and the underlying water table; i.e., there is no vertical leakage into the subsurface from the atmosphere. Repeated SVE field tests exhibited data responses that were not consistent with a confined flow model. It appeared that overlying asphalt and concrete are not completely air-tight. Therefore, this paper explores and develops a transient soil vapor extraction (SVE) testing method that considers the effects of vertical air leakage. The method is a corollary to the Hantush-Jacob (1955) leaky-confined analytic flow model. In all cases considered, the confined flow model was less representative than the leaky condition. Analytic methodologies are developed that allow use of commonly available ground water flow type-curves to evaluate SVE test data. The study indicates that vertical air leakage causes a general increase in the time required to achieve cleanup of contamination, and decreases the radial effectiveness of SVE. The confined flow model was shown to overpredict soil permeability, resulting in further bias toward unreasonably rapid and radially efficacious cleanup estimates. Results of the study also imply that Darcy's Law is valid for most vapor flow conditions. This suggests that other subsurface conditions besides leakage can be evaluated with the appropriate flow model prescribed by site geologic conditions. For instance, anisotropic flow could be considered at sites where fractures or depositional setting suggest contrasts in permeability tensors. It is also suggested that numerical models may be used to simulate vapor flow in heterogeneous settings., San Diego State University
A two-dimensional, finite-difference model of the phase distribution and vapor transport of multiple compounds
Prediction of the transport of volatile mixtures within unsaturated soil can be complicated by the interaction of chemical compounds with variable physical properties. The analysis and design of vapor-extraction remedial systems depends on models which can simulate the chemical and physical factors affecting the removal of vapor-phase chemical mixtures (such as gasoline). Present models fall into two categories: 1) non-dimensional (no transport), multi-compound phase distribution models or 2) multi-dimensional, single-compound transport models. In this thesis, a numerical simulation is presented which couples the steady-state vapor flow equation, the advection-diffusion transport equation, and a multiple-compound, four-phase equilibrium model. The simulation allows spatially variable fields of permeability, surface leakage, and initial contaminant concentrations. The user can specify the location and discharge rates of any number of extraction or injection wells, including zero wells, in which case the simulation will solve transport by diffusion only. The utility of the model is shown by solving the remediation, by vapor extraction, of hypothetical gasoline spills in natural (non-ideal) conditions. The non-ideal conditions include inhomogeneous soil permeability, irregular surface leakage (from fill areas or surface seals), and irregular contaminant distribution. The model is also run in the pure diffusion mode to show the limitations of three-phase (no separate-phase), single-compound vapor flux models in predicting chemical fate and transport., San Diego State University
A vertically-oriented, groundwater flow and solute transport model of the upper Coachella Valley, Riverside County, California
Since 1973, groundwater in the Coachella Valley, California, has been artificially recharged with water from the Colorado River, which has a higher salinity than native water. Groundwater levels have risen over 100 m in response and TDS has increased. SUTRA (Saturated-Unsaturated Transport) was used to construct a vertically-oriented, flow and transport model for the period 1973-1989. The model indicates that a low-conductivity layer impedes solute transport. Solute moves more quickly and is less dispersed above the layer than below it. The model also indicates that the regional flow gradient prohibits westerly movement of the solute. The model accurately simulates flow and less accurately simulates transport. Model parameters used are a compromise between flow and transport accuracy. A true three-dimensional model is needed to accurately simulate transport., John Meadows used a map by S.J. Tyley, 1974 as his base map [Figure 1. Page 2]. 1:211,600, San Diego State University
Age and origin of gold mineralization in the southern portion of the Julian Mining District, Southern California
Base map is taken from a map prepared under the direction of the county surveyor of the County of San Diego, California, June 1965. Coordinates for the map are taken from Google Earth imagery. 1:2,400, Plate 1: Geologic map of the Southern Portion of the Julian Mining District of San Diego County, California, The Julian mining district is located in the eastern portion of the western zone of the Peninsular Ranges batholith approximately 60 km northeast of San Diego, and contains the most significant mineral deposits discovered in San Diego County to date. Gold was first discovered in 1869, and following slow development of the mines, two periods of prosperous activity (1870-1876, 1888-1906) produced approximately $5 million (gold then $20.67 per fine ounce). The gold-quartz veins in Chariot Canyon are hosted by the Chariot Canyon fault, a northwest trending shear zone up to 50 m in width that cuts the Triassic(?) Julian Schist to the west and an unnamed tonalite of Cretaceous age to the east. The gold occurs in four subparallel lenticular veins, from less than 0.3 to 2.4 m in width, and is free milling. The quartz is highly strained and fractured, and in some places comminuted by post-mineral faulting. Arsenopyrite and pyrrhotite constitute the metallic gangue but may be auriferous. Two district alteration zones are recognized. The sericitic zone consists of quartz, oligoclase, tourmaline, sericite, garnet, and arsenopyrite. This assemblage occurs adjacent to the veins and affects both the plutonic and metasedimentary wallrocks. The argillic zone consists of variable proportions of clay minerals. It occurs structurally above and is gradational with the sericitic zone. Other alteration types include arsenopyritization, carbonatization, and possibly potassic alteration. Four K-Ar ages were obtained on micas collected from different locations within the vein/alteration system of the Golden Chariot Mine. Biotite from the vein footwall gave a cooling age of 91.3  2.7 m.y., muscovite from the sericitically altered metasedimentary rocks gave 125.6  3.8 m.y., and a muscovite-biotite pair from the sericitically altered mylonitized tonalite gave 68.5  2.1 m.y. and 58.4  3.0 m.y., respectively. Geologic constraints indicate that the 91.3  2.7 m.y. age most closely represents an age of mineralization/alteration. A coexisting quartz-muscovite pair from the sericitic zone gave 180 values of + 17.2 per mil and +14.2 per mil, respectively, with a calculated equilibration temperature of 531C. Fluid inclusion homogenization temperatures determined from tourmaline within the sericitic zone range between 535C and 575C, corrected for 2 kb total pressure and 1 percent salinity. Temperatures recorded from secondary inclusions in the vein quartz were lower at 375-390C. Using 535C, a minimum 180 value of +14.4 per mil was calculated for a fluid in equilibrium with the quartz and muscovite in the sericitic zone, indicating a metamorphic origin for the hydrothermal fluid. Textural and mineral evidence within the Julian Schist, together with geochronologic constraints rules out regional metamorphism as the thermal source of this hydrothermal system. The 91.3  2.7 m.y. cooling age is concordant with cooling ages along the western margin of the large La Posta pluton to the southeast of the district. Thermal models indicate that large volumes of pelitic metasedimentary rock could be rapidly dehydrated by the La Posta pluton, a minimum of 54 km3 per kilometer of contact. Preexisting structures such as the Chariot Canyon fault could then act as conduits for upwardly migrating fluids released from the metamorphic pile., San Diego State University
Aluminum-in-hornblende barometry, amphibole plagioclase thermometry, geochemistry, and petrology of the Middle Jurassic Emigrant Gap composite pluton
In the northern Sierra Nevada, California, at about the latitude of Lake Tahoe, rocks that predate the emplacement of the Cretaceous Sierra Nevada batholith are commonly subdivided into four belts. From west to east the belts are: the Smartville, central, Feather River peridotite, and eastern belts. Cretaceous and younger sediments form the western boundary of the Smartville belt, while the other belts are separated by the Foothills fault system. The eastern belt includes the quartz-rich largely sedimentary rocks of the pre-Late Devonian Shoo Fly Complex, and the remnants of Late Devonian through Permian, and Early to Middle Jurassic arc rocks. The north-to-northwest trending Foothills fault system and related folds and cleavages have been attributed to the Late Jurassic Nevadan orogeny. However, recent work suggests that some of the north to northwest trending structural fabric within the pre-Cretaceous rocks of the four belts may not have formed during the Late Jurassic Nevadan orogeny as previously thought, but instead may have formed between Early and Middle Jurassic time. The Middle Jurassic Emigrant Gap composite pluton, which crops out in the eastern belt, is composed of four major units: hornblende-biotite granodiorite, two-pyroxene diorite, two-pyroxene gabbro, olivine websterite. Geochemical data suggests that the Emigrant Gap composite pluton is: (1) composed of four major units with distinct chemistries (2) calcic according to Peacock (1931); (3) cafemic according to Debon and Lefort (1983) which implies a mantle source or a mixed sialic-mantle hybrid source; and (4) a granitoid emplaced within a volcanic arc. To quantitatively estimate the physical conditions during emplacement of the pluton, microprobe work was completed on eleven samples from the hornblende-biotite granodiorite unit. Pressures across the pluton range from a low of 1.3 kbar to a high of 2.7 kbar with an average pressure of 2.1 ± 0.3 kbar. Temperature varied across the pluton from a low of 602°C to a high of 686°C, with an average of 646 ± 19°C. The Al-in-hornblende barometry and amphibole-plagioclase thermometry is supported by data collected from the contact metamorphic aureole of the Emigrant Gap composite pluton which suggest pressures of ~2.2 kbar and temperatures of ~650 °C. The Middle Jurassic Emigrant Gap composite pluton intrudes a wide variety of rocks which contain a domainal, locally penetrative cleavage that trends ~N20W, and dips ~72 NE. This northwest trending cleavage is deflected into parallelism with the northwestern margin of the pluton and is truncated by the pluton in the southeast. These relationships along with the fact that the Emigrant Gap composite pluton is unstrained suggest that the northwest trending structural fabric in the eastern belt was not produced by the Late Jurassic Nevadan orogeny, but must have formed prior to the emplacement of the Middle Jurassic Emigrant Gap composite pluton., San Diego State University
Amplification of long period ground motion by the Los Angeles Basin
Empirically derived ground motion amplification in the Los Angeles Basin is presented. Data obtained from 15 separate seismic networks in southern California from events recorded between 1998 and 2009 are used to determine spectral response as a function of both basin depth and period. The response associated with basin depth, defined by the 1.0 km/s S-wave velocity isosurface, increases monotonically with depth for the horizontal component, and nearly monotonically for the vertical component for each oscillator period. This trend is similar for the 2.5 km/s S-wave velocity isosurface, though less smooth, especially when data is processed in smaller bins (500m). These results show consistency with amplifications derived from synthetic data in earlier studies. Additionally, amplification factors are similar to previous empirical studies, ranging from roughly 3.8 for the vertical component to about 4.2 for the horizontal component., San Diego State University
An evaluation of field capacity as a parameter for groundwater recharge estimates
The soil moisture balance method for estimating groundwater recharge assumes that a minimum amount of infiltration is required before recharge may occur. This minimum condition is typically assumed to be field capacity. The method a1so assumes that after this minimum is reached, all infiltration recharges the saturated zone. Consistent discrepancies between field and laboratory specific retention tests indicate the need to reevaluate the above assumptions. The objective of this study is to evaluate the discrepancies between laboratory and field specific retention tests and to determine if the concepts of specific retention and field capacity are relevant to estimations of groundwater recharge. The objective is addressed by answering the following six questions: 1) Is there a minimum amount of infiltration required before groundwater recharge occurs? 2) If so, how does the minimum infiltration value relate to field capacity? 3) Does all infiltration that occurs after field capacity has been satisfied recharge the groundwater? 4) Do field capacity measurements provide moisture contents that are at steady state equilibrium with the water table? 5) Can the moisture contents from the field capacity measurements be re1ated to the characteristic curve? 6) Why is there a consistent discrepancy between the results of the laboratory and field procedures used by consultants to measure field capacity? Field work was conducted at one location in the Fallbrook series, B phase soil in East San Diego County. Four different methods were used to measure specific retention: (1) laboratory drainage, (2) small-area field drainage, (3) large area field drainage, and (4) characteristic curve inflection point. The effective depth of evaporation was estimated on the basis of field hydraulic head gradient measurements and numerical model results. A one-dimensional unsaturated flow model was written to determine the minimum amount of water required to infiltrate a dry soil profile prior to recharge (critical infiltration value). The model was also used to determine the moisture content distribution of a draining soil over an extended period of time. Additionally, numerical simulations were also conducted to determine the importance of the lower boundary condition on 1aboratory specific retention tests. Severa1 methods were used to create characteristic and conductivity curves to use as a data base for the model. Field measured characteristic curves and pressure plate derived conductivity curves were the input data actually used by the model. Based on the results from the specific retention procedures and the numerical model the following conclusions can be made. A minimum amount of infiltration is required prior to groundwater recharge. This minimum is equivalent to the available water capacity as measured by the large-area field drainage procedure. All infiltration in excess of the available water capacity does not recharge the groundwater. The amount lost to evapotranspiration is significant. Specific retention values measured in this study were not in equilibrium with the water table elevation nor are they related to the soil's characteristic curves. The small-area field specific retention test is vertical subject to high horizontal tension gradients that unrealistically limit the extent of vertical flow. Laboratory specific retention tests are controlled by the proximity of the atmospheric lower boundary and the PET rate in the 1aboratory. Results of these methods are representative of field conditions. The Soil Moisture Balance method may be able to provide reasonable estimates of groundwater recharge if the amount of infiltration lost to evapotranspiration, after the available water capacity is met, could be estimated. The increased cost of such an analysis, in conjunction with the increased cost to properly measure available water capacity, advocates that a numerical model to estimate recharge be developed., San Diego State University
An evaluation of the VLF geophysical technique applied to the siting of water wells in a fractured crystalline rock terrain
In the fractured crystalline rock terrains of eastern San Diego County, where residents are dependent on groundwater, wells with low or even insufficient yields are common. Most known high yield wells in this area are located on or near lineaments identified from air-photographs. It is a well-established technique to site wells on these lineaments in order to benefit from the increased permeability commonly associated with these features. The VLF method has the potential to verify the presence of subsurface conductive zones associated with saturated fracture systems. In addition, there is the potential to identify conductive features where no mapped air-photo lineaments exist. If further characterization of the location and subsurface orientation of subsurface fracture zones is possible with the VLF method, improvement might be made in siting wells for increased yields. 40 VLF surveys were conducted in Lee Valley California, where a detailed map of air-photo lineaments was previously produced 19 VLF surveys crossed mapped air-photo lineaments. VLF anomalies were observed in 18 of these locations. Anomalies were also observed in 3 of 4 locations where lineaments can be extrapolated into the basin from areas where they are better exposed. VLF anomalies were also identified in areas where no mapped or extrapolated air-photo lineaments exist. Two dipole-dipole resistivity surveys in these areas indicate that VLF anomalies result from shallow conductivity contrasts as well as deeper structural features. Surveys were conducted in the vicinity of three high yield wells in different areas of eastern San Diego County in order to evaluate VLF response in areas with known hydraulic characteristics. In all three locations VLF anomalies were observed. Estimation of dip directions at these locations corresponded to the expected direction based on the position of the well and the mapped lineaments. A well was sited in Descanso California based on VLF anomaly positions. This well appears to have intersected a shallow conductive zone and exhibits a relatively high yield. The data collected for this study indicate that the VLF method is a useful tool in the location of structures associated with increased permeability in a fractured crystalline rock environment. The sensitivity to small conductivity contrasts suggests that this technique is best applied in areas where additional control, such as mapped air-photo lineaments, exists., San Diego State University