Analysis of well hydrographs in karst aquifer:esti- mates of specific yieldsand continuum transmissivities

Hydrograph analysis techniques have been well developed for hydrographs obtained from streams and springs, where data are cast in terms of total discharge. The data obtained from well hydrographs provide water level versus time; hence, a method of hydrograph analysis is required for situations in which only water level data are available. It is assumed here that three segments on a recession curve from wells in a karst aquifer represent drainage from three types of storage: conduit (C), fracture (F) and matrix (M). Hydrographs from several wells in a karst aquifer are used to estimate the specific yields (Sy) associated with each portion of the aquifer (C, F, M), as well as continuum transmissivities (T). Data from three short injection tests at one well indicate continuum T at this well bore is approximately 5 m2 day−1, and tests at numerous other wells in the aquifer yield results between 1 and 7 m2 day−1. The T estimated with well hydrographs from two storms indicates a T of 9.8 m2 day−1. Well-developed conduit systems in which water levels in wells show a flashy response typically show Sys of 1 × 10−4, 1 × 10−3, and 3 × 10−3 for C, F, and M, respectively. Less well-developed conduit areas show more nearly equal Sys (8.6 × 10−4, 1.3 × 10−3, 3 × 10−3). Areas with no evidence for the presence of conduits have only one, or in some cases two, slopes on the recession curve. In these cases, water-level responses are slow. Recession curves with a single slope represent drainage from only the lower T matrix. Those with two slopes have an additional, more rapid response segment on the recession curve which represents drainage from the higher T, lower Sy, fractures in the system

Chemical and isotopic investigation of the new hydrothermal system at Mount Saint Helens, Washington

Online access for this thesis was created in part with support from the Institute of Museum and Library Services (IMLS) administered by the Nevada State Library, Archives and Public Records through the Library Services and Technology Act (LSTA). To obtain a high quality image or document please contact the DeLaMare Library at https://unr.libanswers.com/ or call: 775-784-6945.The behavior of young (0m) and driven by post-eruption recharge. Thermal areas occur on and north of the volcano and these areas are not currently related through a lateral How system. Recharge to the geothermal area on the volcano is in the crater, with fluids discharging toward the north. Fluids on the volcano obtain the majority of their heat from the magma conduit, and geothermal waters contain up to LS% magmatic water which contributes up to 70% of the Cl found in the waters. Air and meteoric water have been circulating through the intracrater dome complex since 1980. Samples of fumarole steam condensates collected in this study have been variably mixed with meteoric water and have contained 50 to 70% magmatic water from 1986 to 1988. The compositions and temperatures of geothermal waters have been changing with time and with increasing distances from the dome. The system as a whole has cooled with time and its TDS has been decreasing with time. Although the geothermal waters do not appear to have attained equilibrium with host rocks, they have begun to stabilize

Processes controlling colloid composition in a fractured and karstic aquifer in eastern Tennessee, USA

Groundwater was sampled from a number of wells along recharge pathways between fractured shale and karstic formations to evaluate the chemical and hydrologic mechanisms controlling the nature and abundance of groundwater colloids. The colloids recovered using low flow rate purging and sampling exhibited a composition and abundance consistent with lithology, flow paths, and effects of hydrology and aqueous chemistry on colloid mobilization and stability. In general, the larger-size colloids and Ca-containing colloids were more abundant in the karstic lithologies, while Na-containing colloids were more important in the shales. The composition of the colloids reflected recharge pathways from the fractured shale and dolomite formations on the ridges into the limestone in the valley floor. The Mg-colloids in the limestone reflect the possible contributions from the dolamite, while the Na, K, and Si reflect possible contributions from the shale. However, it was not possible to use the colloid composition as a signature to demonstrate colloid transport from one lithology to another. Mixing of recharge water from the shale with groundwater within the limestone formation and precipitation/dissolution reactions could account for the colloids present in the limestone without invoking transport of specific shale-derived colloids into the limestone formation. The abundance of colloids in groundwater appears to be controlled by both chemical factors affecting colloid stability, as well as physical factors related to hydrology (storm-driven recharge and water velocities). In general, colloids were more abundant in wells with low ionic strength, such as shallow wells in water table aquifers near sources of recharge at the top of the ridges. Increases in cation concentrations due to dissolution reactions along flow paths were associated with decreases in colloid abundance. However, in spite of elevated ionic strength, colloid concentrations tended to be unexpectedly high in karstic wells that were completed in cavities or water-bearing fractures. The higher levels of colloids appear to be related to storm-driven changes in chemistry or flow rates that causes resuspension of colloids settled within cavities and fractures

Hydrogeochemistry and preliminary reservoir model of the Platanares Geothermal System, Honduras, Central America

A detailed hydrogeochemical investigation has been performed at Platanares, Honduras in preparation for shallow geothermal exploration drilling. Platanares is not associated with any Quaternary volcanism but lies in a tectonic zone of late Tertiary to Quaternary extension. Thermal fluids are characterized by pH between 7 and 10, Cl SO/sub 4/ > Cl, B less than or equal to 17 mg/l, Li less than or equal to 4 mg/l and As less than or equal to 1.25 mg/l. Various geochemical indicators show that mixing of hot and cold end-member fluids is an important hydrologic process at this site. Geothermometers indicate the geothermal system equilibrated at roughly 225/sup 0/C while trace element chemistry indicates the reservoir resides in Cretaceous red beds of the Valle de Angeles Group. Based on the discharge rates of thermal features, the minimum power output of the Platanares geothermal site is about 45 MW (thermal)