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USGS Southeastern Coastal Plain Project
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Coastal Plain Drilling Program - Fall 1997

A new hydrogeologic test hole was drilled at Swansea, Lexington County, South Carolina, between October 15 and November 4, 1997. This continuously cored test hole penetrated the entire Coastal Plain section and reached sub-Coastal Plain crystalline rocks at a depth of 528 ft. The total depth of the corehole was 548 ft beneath a surface elevation of 367 ft. Two monitoring wells were installed at the site. This drilling project was done in cooperation with the South Carolina Department of Natural Resources (DNR). The Swansea corehole is located at the Swansea Elementary School where a DNR-USGS Science Fair was held for the students and faculty. Core samples, other sediment and fossil samples, as well as the drill rig, were on display. Discussions of geology and hydrology were provided by the USGS and DNR scientists and drillers.


Coastal Plain Drilling Program - Spring 1997

In cooperation with the South Carolina Department of Natural Resources (DNR), a new hydrogeologic test hole was drilled between mid-April and late May, 1997 at the Clark Middle School in Orangeburg, SC. This test hole was continuously cored through the Coastal Plain sediments and reached underlying Triassic redbeds at a depth of 1,116 ft. A screen was set opposite an Upper Cretaceous sand aquifer, and the resulting well will be used as a water-level monitoring site. Students and teachers from Clark School visited the drilling operation on May 19 and 20. The core samples from the drill hole, along with a fossil display and other geologic and hydrologic equipment, were on display for the visitors, and discussions of geology and ground water were presented by DNR and USGS scientists.


Deep Testhole in Jasper County, South Carolina

The Southeastern Coastal Plain Project is participating in the study of a 2,900-ft-deep hydrogeologic testhole (testhole C-15) at Gillisonville in Jasper County, South Carolina. This test was drilled and logged commercially for the South Carolina Department of Natural Resources (DNR) with funding support from the U.S. Department of Energy - Savannah River Site. USGS paleontologists are providing biostratigraphic analyses of sidewall cores taken in the Coastal Plain section of the hole. Preliminary analysis of fossil calcareous nannofossils (microscopic golden-brown marine algae) indicates that about 1,000 ft of Cenozoic sediments, principally Tertiary deposits, are present above about 1,800 ft of Upper Cretaceous deposits. The results of the preliminary biostratigraphic study are available as USGS Open-file Report 97-155 . DNR is conducting hydrogeologic and stratigraphic analyses of the cores, cuttings, and geophysical logs from the testhole.


Coastal Plain Drilling Program, Fall 1996

The USGS Southeastern Coastal Plain Project drilled two continuously sampled stratigraphic and hydrologic testholes in northeastern Charleston County, South Carolina, during October-November, 1996.The first testhole was drilled at Moore's Landing in the Sewee Bay 7.5-minute quadrangle on land managed by the U.S. Fish and Wildlife Service. Beneath a thin section of surficial deposits, this testhole encountered Tertiary limestones, sands, and clays to a total depth of 369 ft. The Moore's Landing testhole bottomed in lower Paleocene sediments. The second testhole was drilled at the Santee Coastal Reserve on land managed by the South Carolina Department of Natural Resources. This testhole encountered Quaternary, Tertiary, and Upper Cretaceous deposits to a total depth of 545 ft. The Santee Coastal Reserve testhole bottomed in muddy sands of late Campanian (Cretaceous) age. Both Charleston County testholes were left open to the Tertiary limestone aquifer. Groundwater extracted from selected core samples was collected by a USGS hydrologist for chemical analysis. Geophysical logs were run in both testholes by the South Carolina Department of Natural Resources. The core drilling was done by the USGS Eastern Region Geologic Mapping Team's drill crew. This drilling program is a cooperative effort of the South Carolina Department of Natural Resources and the USGS.


Coastal Plain Drilling Program, Spring-Summer 1996:

The USGS Southeastern Coastal Plain Project drilled four stratigraphic-hydrologic testholes in the South Carolina Coastal Plain between May and September, 1996. A 432-ft-deep testhole was completed at Myrtle Beach (Horry County) during May; a second testhole was drilled to a total depth of 647.5 ft in June at Little Peedee State Park (Dillon County). A third testhole was drilled to 554 ft in July at Lee State Park near Bishopville (Lee County), and a fourth testhole was drilled in September at Horrell Hill School (Richland County) to a depth of 469 ft. This drilling program is a cooperative effort of the South Carolina Department of Natural Resources (SCDNR) and the USGS.

Each testhole was continuously cored to produce a nearly complete sample record of the sand and clay layers that constitute the Coastal Plain section. One aquifer was screened in each hole for use in the SCDNR monitoring-well program. Geophysical logs were collected in each testhole by the South Carolina Department of Natural Resources. The core drilling was done by the USGS Eastern Region Geologic Mapping Team's drill crew.

The new Myrtle Beach testhole complements an earlier SCDNR hole drilled at the same site as part of an aquifer storage and recovery feasibility study. The SCDNR hole penetrated the entire Coastal Plain section and encountered weathered crystalline rocks near a depth of 1,400 ft; however, core samples were not taken above a depth of 376 ft in that hole. Therefore, the interval from ground surface to a depth of 432 ft was continuously sampled in the new USGS hole. The "principal aquifer" in the Myrtle Beach area, centered at a depth of about 400 ft, was screened in the USGS hole.

The Little Pee Dee State Park testhole encountered Cretaceous deposits beneath 22.5 ft of surficial sand. Cretaceous sands and clays continued to a depth of 627.7 ft where saprolitic mudstone of presumed Triassic age was encountered. A monitoring well was installed with the screen set in the first sand above the Cape Fear Formation (Cretaceous).

The stratigraphic section in the Lee State Park testhole consists primarily of Cretaceous sands and clays to a depth of 537 ft where basement rock (quartz-muscovite phyllite) was encountered. Beneath a thin section of Tertiary deposits, Cretaceous sands and clays are present to a depth of 455 ft in the Horrell Hill testhole. Amphibolitic gneiss constitutes the basement section below that depth at Horrell Hill.


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