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Ground-Water Study of the Toyota Motor Manufacturing Site: Georgetown, Kentucky
by Lyle V.A. Sendlein, Theresann Dowdy
and Daryl Hines--KWRRI
Gary Felton--Kentucky Geological Survey
University of Kentucky
Karst terrain is a specific type of topography that is usually underlain by carbonate rocks that have been altered by chemical dissolution. Characteristic karst landforms found within the study area include sinkholes, springs, and losing streams. Within the study area, 62 sinkholes were identified from the four 7.5 minute topographic maps. Additionally, 120 sinkholes were identified from the aerial photographs and field reconnaissance. Of these 182 sinkholes, 51 were found to be located on the nearly 1,250-acre TMM property. Most of the sinkholes were either destroyed or covered up by construction of the TM structures and parking lots. A number of springs have been identified within the study area and the TMM site. These springs range from constant trickles of water, to wet weather springs, to springs that were large enough to supply a domestic household in earlier times, to larger springs, such as Marshall Spring. Swallets are openings to the subsurface conduit system. They often occur in sinkholes, but some may occur in stream channels. Swallets that occur in stream channels are direct recharge points to the conduit system. Eight springs and 2 swallets were found on the TMM site.
Dye trace analysis was performed to determine connectivity and help to build a conceptual model of the subsurface flow system. The rocks are primarily limestones with inter-fingering shale units. Where the shale units are thicker and widespread, less conduit development has occurred and the ground water moves through fractures that range from well to poorly integrated. The shale impedes downward water movement and causes the water to move laterally, where it emerges on the surface as seeps or small springs. Where the fractures are better integrated, larger springs were present.
To fully characterize the ground water at the TMM site using monitoring wells would require a large number of wells, because each well would sample only a small part of the ground-water system. In this kind of flow system, monitoring springs in combination with wells can be the most effective method.
The ground-water flow beneath the deep basements was essentially isolated from the surrounding ground-water systems because the sump systems in the buildings maintained a continuous flow toward the TMM buildings. Sump systems are used to dewater basements and pit areas of some structures on the site. The sump system consists of gravel drainage layers, drainage tiles, sump pit, and sump pump. Drainage tiles were installed along the lower perimeters of the outer walls of the basement and pit areas. The tiles collect and channel ground water to the sump pits. Located within the sump pits, the sump pumps mechanically pump the collected ground water out of the system. The sump areas and their related drainage tile fields represent ground-water discharge zones. These systems are located below the shallow ground-water table and draw water from this zone to the sumps. Due to the nature of the bedrock, this "zone of isolation" extended no more than seven to fourteen feet away from the edge of the buildings. In such a setting, buildings with sumps would not be sources of contamination to the surrounding ground-water systems. There is a deep ground-water zone in the eastern part of the TMM site that does not have significant subsurface water movement or surface connectivity.
Most ground water in the zone near the surface of the TMM site is derived from infiltration onsite. This water flows rapidly for short distances. It exits the ground in small hillside seeps and springs that are typically either at the soil-bedrock interface or at the upper surface of the Millersburg formation. This formation is approximately 25 feet in elevation below the TMM plant site. Because the ground-water surface is controlled by the soil-bedrock interface, the near-surface ground-water flow will be related to the bedrock topography. The ground-water movement will be down gradient toward depressions in the bedrock surface such as small gullies or valleys and any remnants of sinkholes that were left behind after construction.
Major conduit development appears to occur near the interface between the Tanglewood and Grier formations, with most of the development in the Grier Formation. This development also is related to the major fracture trends in the area. Off the TMM site, in the deep Tanglewood or Grier (Figure 1), there are two major conduits systems that are connected to the surface by a swallett in Dry Run to the west and a swallett in Lanes Run to the east. The Dry Run swallett is connected to the conduit system that discharges at an unnamed spring (called Railroad Spring in this study) and the Lanes Run swallett is connected to a conduit system that terminates at Marshall Spring.
Two different types of karst systems have been described. The first is the deep-flow system, typical of the conduit between Lanes Run and Marshall Spring, and the second is the shallow epikarstic system, which is typified by the conduit between the sinkhole near the Child Care Center and Darby Spring. Velocity in the karst conduit systems ranged from 192 ft/day to 6,000 ft/day, based on four dye traces.
In summary, the near-surface ground-water system (epikarstic system) has been disturbed by the construction on the TMM site. Deep basements with sump systems drain local areas adjacent to the basements. Portions of the shallow ground water discharge as springs and seeps to the surface water system. Deeper ground water flows in two isolated conduit systems that are accessed in the vicinity of the TMM site by swallets in Lanes Run and Dry Run streams.
Last modified: December 5, 1996