Georgia Geologic Survey Information Circular 99
The Millhaven site, located in northeastern Screven County, Georgia, was developed during 1991-94 to better characterize the geologic, hydrologic, and water-quality characteristics of a multi-aquifer system in Coastal Plain sediments as part of an evaluation of ground-water flow and stream-aquifer relations in the vicinity of the U.S. Department of Energy, Savannah River Site . The test site consists of a 1,452-foot deep corehole drilled into sediments of Late Cretaceous age. and five test wells developed at depths ranging from 50 to 1,380 feel. Data from the test wells are presented for 1991-95. Examination of the lithology and paleontology of core indicated that Coastal Plain sediments in the vicinity of the site are of Late Cretaceous through Eocene age, deposited mostly under marine, nearshore marine, or nonmarine environments. The test wells were screened in the Floridan aquifer system, Dublin aquifer system, and Midville aquifer system.
Vertical hydraulic conductivity determined from hydraulic analysis of core was 1.15 x 10-5 to 1.19 x 10-1 feet per day (ft/d) in the upper Dublin confining unit, and from 2.83 x 10-6 (estimated) to 1.4 x 10-3 ft/d in the upper Midville confining unit. Horizontal hydraulic conductivity determined from aquifer tests and estimated from borehole resistivity logs was 13 to 70 ft/d in the Upper Floridan aquifer, 42 ft/d in the Gordon aquifer. 7 ft/d in the Millers Pond aquifer. 22 ft/d in the upper Dublin aquifer, and 10 to 22 ft/d in the lower Dublin aquifer.
Water-level measurements indicate a gene ra l upward head gradient at the Millhaven site, indicative of an area of potential upward discharge. The water level in the Upper Floridan aquifer responded to extreme changes in Savannah River and Brier Creek stages and showed little response to precipitation at Sylvania, Ga. Water levels in the lower Dublin and lower Midville aquifers responded little to precipitation, or to Savannah River or Brier Creek stages.
Water sampled from each of the five water-bearing zones completed at the Millhaven site is soft. low in dissolved solids, and, with the exception of high concentration of iron in the lower Dublin aquifer, is considered to be suitable for most uses. Water in the lower zone of the Upper Floridan aquifer may be distinguished from water in the upper and middle zones of the Upper Floridan by higher concentrations of dissolved solids, alkalinity as CaC03, silica, calcium. magnesium. and strontium. Water in the Upper Floridan aquifer may be distinguished from water in the underlying lower Dublin and lower Midville aquifers by higher concentration of calcium and lower concentration of sodium. Water in the lower Dublin aquifer may be distinguished from water in the underlying lower Midville aquifer by its higher concentrations of iron. manganese, potassium, chloride, and sulfate.
The upper and middle zones of the Upper Floridan aquifer are hydraulically well connected at the Millhaven site. as evidenced by minimal head difference between the zones, similarity of water-level fluctuations and trends, drawdown response during aquifer tests, and similarities in water chemistry. The lower zone of the Upper Floridan aquifer is hydraulically separated from the overlying middle zone as was indicated by differences in water quality, a slight upward head gradient, and differences in water-level fluctuations between the lower zone and the upper two zones. Although hydraulically separated under static conditions, interaquifer leakage between the lower zone and the upper two zones was indicated by drawdown response during aquifer tests.
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Purpose and scope
Description of study area
Well construction and coring
Hydraulic conductivity of core samples
Hydraulic conductivity estimated from borehole resistivity
Appendix-Lithologic description of Millhaven core