Masters Theses

Date of Award

8-1995

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Claudia I. Mora, Robert D. Hatcher

Committee Members

Larry D. McKay

Abstract

Springs are natural monitoring points useful in characterizing hydrogeologic systems because their discharge represents a principal component of flow in the subsurface. An area within the Valley and Ridge province, southeast of Oak Ridge, Tennessee, was studied to determine general spring characteristics, the conditions and processes controlling subsurface flow, and the potential for deep, basinal flow contributions to the shallow groundwater system. During this investigation, 217 springs were located, and a detailed study of 38 of these springs was conducted, including monthly monitoring of temperature, specific conductance, yield, dissolved oxygen, and pH. Two hydrologically distinct units exist in the study area; the Knox aquifer, consisting of Cambrian to Ordovician carbonates, and the aquitards, consisting of interbedded carbonates and elastics above and below. The Knox aquifer is a mature conduit-controlled karst unit represented primarily by perennial spring discharge water not directly influenced by seasonal effects of precipitation. Groundwater flow processes in this unit include both point and dispersed recharge, low to moderate storage, with rapid flowthrough in the highly conductive, well-connected conduit system; and moderate to high storage in the less conductive diffuse system. Because of the karst nature of the carbonate units, active flow in the Knox aquifer is deeper overall than flow in the aquitards. The aquitard units, characterized by shallow fracture-flow systems, are represented by a large number of perennial and ephemeral springs heavily influenced by the seasonal effects of precipitation. Groundwater flow processes of this unit include dispersed surface recharge, low to moderate storage, and rapid flowthrough in the highly conductive, shallow fracture system. Spring yields from the Knox aquifer account for approximately 70 percent of the total discharge from springs in the study area despite representing only 26 percent of the observed springs. Based on the assumption that all of the spring discharge is coming from the saturated groundwater zone, simple water budget calculations reveal that approximately 16.8 cm/year and 2.0 cm/year discharge the Knox aquifer and aquitard saturated groundwater zones, respectively. The water budget result for the Knox aquifer indicate that previous estimates of recharge are underestimated by a factor of two, while the results for the aquitards are in agreement with previous estimates. Major and trace ion geochemical data suggest that most of the springs discharge water that flows through a single lithology, supporting the concept of active, relatively shallow circulation. Geochemical observations indicate that a few springs may receive groundwater contributions from other lithologic units, suggesting a possible contribution from deeper groundwater zones. Analyses of He also indicate that some springs within the aquifers may have deep basinal flow contributions, while quantitative results of H-O stable isotope analyses indicate a subsurface flow system recharged exclusively by meteoric water. Most of the data suggest that groundwater flow paths are all relatively shallow and are probably confined to a local ridge recharge-valley discharge system, although the possibility that of some flow contribution having deep basinal origins cannot be entirely dismissed.

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