Date of Award

5-1998

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Larry D. McKay

Committee Members

Claudia Mora, James Smoot

Abstract

In East Tennessee, the Tennessee River and its tributaries cut across many of the sub-parallel strike valleys in the Valley and Ridge several times, including the karstic carbonate strike belts within them. The construction of dams along the Tennessee River and its tributaries, including the Clinch River, has increased the river stage between 5 and 20 m, which caused inundation of considerable areas. This also raised the baselevel for drainage, thus altering the groundwater regime within the valleys intersected by these rivers. The stud area addressed in this research includes an industrial facility situated on karstic carbonate bedrock which is bounded by a Tennessee Valley Authority-controlled run-of-the-river surface impoundment, the Clinch River, and Poplar Cree, a large first order tributary to that impoundment. Surface water flow and state conditions in these water bodies are dictated by reservoir operations at upstream and downstream dams. Surface water stage plays a major role in regulating overall groundwater flow from the facility.

Typically, the master surface water drains represent baselevel for groundwater discharge and it was expected that large springs, reflecting the karstic nature of the bedrock underlying the site, would occur along these surface water bodies. However, a comprehensive inventory of springs and seeps within this study area identified only a few small seeps near the impoundment, most of which are transient in nature. Consequently, it was expected that much of the groundwater discharges to surface water via subaqueous springs possibly related to pre-impoundment baselevel conditions. Remote methods such as infrared thermography were attempted in order to locate potential zones of subaqueous groundwater discharge but proved unsuccessful.

This study documents an attempt to identify direct subaqueous discharge of groundwater to a flowing surface water body on the basis of inherent differences in temperature and specific conductance between groundwater and the receiving surface water. This approach was applied to a study area which includes the East Tennessee Technology Park (ETTP) located within the Department of Energy Oak Ridge Reservation in east Tennessee. The site is bounded by the Clinch River, a run-of-the-river impoundment and Poplar Creek, a large first order tributary to that impoundment. The geology at this site is highly complex, reflecting structural and stratigraphic controls on groundwater flow, all of which have been overprinted by karst dissolutional processes and the effects of reservoir impoundment and operation.

In this effort, a multi-parameter probe was suspended below a small boat and trolled along the bottom of a run-of-the-river impoundment in water depths ranging from ~1 to 16 m. Temperature, specific conductance, dissolved oxygen, head, bathymetry, and boat/probe position were continuously recorded along multiple survey runs oriented roughly parallel to shoreline at 1 - 10 m spacings. Real-time corrected Global Positioning System (GPS) technology was used to provide sub-meter resolution of probe and boat position. Water quality and GPS data were integrated and recorded using onboard portable computers.

Field work was completed over and 18-day period in late January to early March 1996. A total of 152 survey runs were performed over nearly 12 km of surface water, yielding more than 157,000 records. From this data, a total of 198 anomalies where identified. Anomalies ranging up to 0.74 C and 38 uS/cm were identified, the majority of which were detected in shallow water < 3 m deep. The magnitude of the anomalies identified are within the range predicted using simple mixing models. These models also indicate that given the high ambient flow rates in the river, many low volume subaqueous springs may be below the resolution for detection.

The locations of anomalies identified in this effort were found to coincide with a number of key hydrogeologic features and trends where ground water discharge was expected to occur. The location and character of the anomalies detected appears to represent two distinct modes of groundwater discharge. Where the surface water bodies intersect flowpaths in the saturated overburden above bedrock or, where the creek bottom is mantled with thick alluvium, groundwater appears to discharge as diffuse seepage zones or as continuous seepage face. In contrast, anomalies were more frequently detected where bedrock is exposed along the river/creek bottom. Further, these anomalies were typically of higher magnitude and discrete, representing groundwater discharge along primary bedrock flowpaths. These include solutionally enlarged fractures, faults, and conduits.

The dynamic nature of the bounding surface water bodies in this study area results in highly variable and transient patterns of groundwater discharge. It is likely that subaqueous springs inferred from the anomalies are part of a highly complex, interconnected distributary network that functions differently in response to the highly transient surface water boundary conditions.

The results of this study support the findings of a previous water balance study, indicating that the majority of groundwater discharge from the ETTP site is occurring through subaqueous discharge to the Clinch River and Poplar Creek. The results further support the contention that there is little potential for significant underflow of these surface water bodies. Direct investigation of subaqueous spring discharge, possibly involving divers and the installation of river bottom seepage meters is recommended to confirm the spring locations identified in this study and to evaluate their role in the overall hydrogeology of the site.

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