Water-Resources Investigations Report 884176 GEOLOGY OF AN AREA NEAR BRENTWOOD, WILLIAMSON COUNTY, TENNESSEE Prepared by the U.S. GEOLOGICAL SURVEY in cooperation with the TENNESSEE DEPARTMENT OF HEALTH AND ENVIRONMENT, DMSION OF SUPERFUND GEOLOGY OF AN AREA NEAR BRENTWOOD, WILLIAMSON COUNTY, ‘TENNESSEE ” By Dorothea Withington Hanchar U.S. GEOLOGICAL SURVEY .a Water-Resources Investigations Report 88-4176 Pepared in cooperation with the TENNESSEE DEPARTMENT OF HEALTH AND ENVIRONMENT, DIVISION OF SUPERFUND Nashville, Tennessee 1988 DEPARTMENT OF THE INTERIOR DONALD PAUL HODEL, Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director For additional information write to: Copiesof this reportcan bepurchased from District Chief U.S. Geological Survey U.S. Geological Survey Books and Open-File Reports Section A413 Federal Building Federal Center, Building 810 Nashville, Tennessee37203 Box 25425 Denver, Colorado 80225 CONTENTS Abstract 1 Introduction 1 Geology 6 Lithology 6 Structure 14 Summary 15 References 24 ILLUSTRATIONS Figure 1. Map showing location of study area and observation and domestic wells 2 2. Map showing structural setting of study area 4 3. Generalized geologic section along lines A-A! and B-B1 across the study area 5 4. Map showing thickness of the Bigby-Cannon Limestone 8 5. Gamma and neutron geophysical logs for well Wm:N-053A 10 6-10. Maps showing: 6. Thickness of the Hermitage Formation 12 7. Thickness of the Carters Limestone 16 8. Structure of the top of the Carters Limestone 18 9. Structure of the top of the Lebanon Limestone 20 10. Structure of the top of the T-3 bentonite bed of the Carters Limestone 22 TABLES Table 1. Thickness of formations 7 2. Depth to the top of formation or unit 11 CONVERSION FACTORS For use of readers who prefer to use metric units, conversion factors for inch- pound unit used in this report are listed below: ., Multiply inch-pound unit BY To obtain metric unit foot (ft) 0.3048 meter (m) foot per mile (ft/mi) 0.1894 meter per kilometer (m/km) mile (mi) 1.609 kilometer (km) Sea level: In this report “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)--a geodetic datum derived from a general ad- justment of the first-order level nets of both the United States and Canada, formerly called “Sea Level Datum of 1929..” . ill GEOLOGY OF THE AREA AROUND A HAZARDOUS-WASTE DISPOSAL SITE IN WILLIAMSON COUNTY, TENNESSEE By Dorothea Withington Hanchar .i ABSTRACT in 1978. In June 1986, the U.S. Geological Sur- vey, in cooperation with the Superfund Division ‘The lithology and geologic structure of an of the TennesseeDepartment of Health and En- area near Brentwood, Williamson County, Ten- vironment, began a study to characterize the nessee, were studied to define the potential hydrogeology of the areas and the surrounding aquifers and confining units of the ground-water area. This characterization includes a thorough flow system. Four formations were identified. understanding of the geology to define the extent They are, in descending order, the Bigby-Cannon of the potential aquifers and confining units that Limestone, the Hermitage Formation, the comprise the ground-water flow system. This Carters Limestone, and the Lebanon Limestone. report describesthe geology of the area and com- The B&by-Cannon Limestone and the Carters pares it to the regional geology. Limestone are potential aquifers. The Her- mitage Formation and the Lebanon Limestone Regionally, the study area is located along are confining units. The Bigby-Cannon Lime- the northwestern dipping flank of the Nashville stone and the Hermitage Formation have been Dome (fig. 2) (Wilson, 1948, p. 57). Previous affected by recent erosion. Any variation of the work by Wilson and Miller (1963) has identified Carters Limestone is controlled by pre-Carters four formations of Ordovician age at or within erosion of the top of the Lebanon Limestone. 300 feet of the land surface that underlie the site The thickness of the Carters Limestone ranges and are discussedin this report. From youngest from 65 to 79 feet. Structurally, the area reflects to oldest these formations are: the Bigby- the regional northwest dip. A small scale anti- Cannon Limestone, and the Hermitage Forma- cline-syncline pair also is evident. This feature tion of the Nashville Group, and the Carters is not a result of erosion and also occurs in the Limestone and the Lebanon Limestone of the T-3 bentonite bed in the Carters Limestone. Stones River Group (fig. 3). These formations have been described in detail by Wilson (1949). Descriptions of the lithologies penetrated INTRODUCTION during the drilling program are presented by Withington (1988). An area near Brentwood,Williamson County, Tennessee (fig. l), was used to dispose A network of 34 observation wells was in- of approximately 800 barrels of industrial waste stalled at 17 sites for this project (Withington, Location map 11 r-ll,dXmWr’ Williamson County Study area EXPLANATION unllllnDISPOSAL SITE A-A’ LINE OF SECTION 53A& OBSERVATION WELL AND NUMBER--FUiI Well identification includes the prefix Wm:N-##. ‘33a DOMESTIC WELL AND NUMBER--Full well indentification includes the prefix Wm:N-##. Figure 1. --Location of study area.and observation and domestic wells. 2 86”d-17’22” 86’45’ 35’58’ 1 -7 ; I ese from U.S. Geologlcel Survey 24.000. IFrenklln. 1991 0 0.5 MILE I I I k I HH 0 0.5 KILOMETER CONTOUR INTERVAL 100 FEE-i DATUM IS SEA LEVEL 3 , , , , 1 . P , ; I t .I u A’ m FEET 0 800- Obc I - ! 700- - \ I oc I 01 500 3 a cl- 64 2 B’ =G 0 700- 600 ’ 2.000 FEET 0I I Vertical exaggeration X 5 DATUM IS SEA LEVEL EXPLANATION GEOLOGIC UNITS Obc Bigb y-Cannon Limestone Nashville Group Oh Hermitage Formation f Ordovician oc Carters Limestone Stones River Group 01 Lebanon Limestone It- Figure 3.--Generalized geologic section along lines A-A’ and B-B’ across the study area. 1988). A shallow well and a deep well were ty (Wilson, 1948, p. 114). The Bigby facies is a drilled at each site. Major changes in lithologic coarse-granular limestone, composed of fossil type were identified on the basis of the lithology, fragments, and is blue-gray in color when fresh texture, and color of the cuttings, which were col- (Wilson, 1949, p. 115). The dove-colored facies lected every 5 feet during drilling of the wells. interfingers with the Bigby and the Cannon Upon completion of drilling, the deep wells were facies and is a light-gray (“dove-colored”) logged by using caliper, gamma, and neutron lithographic limestone (Wilson, 1949, p. 122). borehole-geophysical tools (Withington, 1988). Formation contacts were identified on the basis The Cannon facies, which also interfingers of interpretation of both lithologic and geophysi- with the Bigby facies, is a fine- to medium- cal logs. grained blue limestone with coarse-grained variations (Wilson, 1949, p. 126). In the study Geophysical logs obtained from five area, the Bigby and the Dove-colored facies were domestic wells near the study area (fig. 1) were recognized. The formation is predominantly used to supplement lithologic data derived from silt-free with solution openings, making this unit drilling operations. The wells from which these a potential aquifer where solution openings are logs were obtained ranged in depth from 148 to present. The Bigby-Cannon Limestone is a 1,050 feet. The geophysical logs from these wells coarse- to medium-grained, dark yellowish- were used in conjunction with the lithologic and brown limestone with interbeds of dove-colored geophysical logs of the Geological Survey obser- lithographic limestone. Regionally, the thick- vation wells to construct structure contour and nessof this formation ranges from 50 to 100 feet. formation thickness maps. In the study area, this formation has been thinned by recent erosion, and the thickness ranges from0 to 41 feet (table 1; fig. 4). The max- GEOLOGY imum thickness does not represent a complete section. The contact between the Hermitage Lithology Formation and the Bigby-Cannon Limestone is transitional and is based on texture and color The formations in the study area are, in changes seen in the cuttings during drilling as descending order, the Bigby-Cannon Limestone, well as changesseen in the geophysical logs. The the Hermitage Formation, the Carters Lime- Bigby-Cannon-Hermitage contact is seen in -stone, and the Lebanon Limestone. These units gamma logs by an increased number of gamma are overlain by 3 to 15 feet of soil and weathered counts per second, which corresponds to an in- rock. This material is generally brown to red- creased shale content in the Hermitage Forma- dish-brown clay and silt. All drilling, once tion (fig. 5). This contact was determined in through the weathered rock, began in either the neutron logs by an increase in counts per second, Bigby-Cannon Limestone or the Hermitage For- indicating decreasedporosity with depth (fig. 5). mation. The Hermitage Formation is partially eroded. Depth to the top of the Hermitage ranges from Regionally, the correlative Bigby and Can- 0 to 41 feet (table 2; fig. 3). non Limestones (referred to as the Bigby- Cannon Limestone in this report as defined by The Hermitage Formation consists of four Wilson, 1947) consists of three major lithologic facies. These are (in de‘scending order): the types: the Bigby facies, the dove-colored facies, Dalmenella Coquina limestone, the silty nodular and the Cannon facies (Wilson, 1949,p. 107). All limestone, the granular phosphatic limestone, three types occur in northern Williamson Coun- and the laminated argillaceous