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Lithostratigraphic and Hydrogeologic Characteristics of the Ordovician Sinnipee Group in the Vicinity of Waupun, Fond du Lac County, Wisconsin, 1995–96

By Charles P. Dunning and Douglas J. Yeskis

This report is available for download as a PDF (1,954 KB).

Table of Contents

Abstract
Introduction
Purpose and Scope
Description of Study Area
Methods of Study
Borehole Construction and Development
Rock Core Evaluation
Borehole Geophysical Surveys
Ground-Penetrating Radar Surveys
Aquifer Tests
Static Water-Level Measurement
Displacement/Recovery Tests
Multiple-Well Constant-Discharge Tests
Water-Sample Collection
Lithostratigraphy
Hydrogeological Characteristics
Rock-Matrix Properties
Water Type and Chemical Characteristics
Hardgrounds, Fractures, and Bedding-Plane Partings
Hydraulic Properties
Vertical-Flow Characteristics
Horizontal-Flow Characteristics
Anisotropy
Summary
Acknowledgments
References Cited
Appendix 1: Laboratory Procedures for Porosity and Density Analysis of Rock Core Samples
Appendix 2: Water levels observed in boreholes above, below, and in the packed interval during multiple-well constant-discharge tests

Figures

Figure 1. Map showing location of study site in the vicinity of Waupun, Fond du Lac County, Wis.

Figure 2. Schematic drawing showing the approximate location of boreholes FL-800, FL-801, and FL-802, and monitoring wells at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Figure 3. Caliper logs showing intervals isolated by packers for boreholes FL-800, FL-801, and FL-802 at the study site in the vicinity of Waupun,
Fond du Lac County, Wis.

Figure 4. Generalized stratigraphy of the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Figure 5. Diagram showing geophysical logs, televiewer image, generalized core description, heat-pulse flowmeter data, and relative permeability plot for borehole FL-800 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Figure 6. Diagram showing geophysical logs, televiewer image, heat-pulse flowmeter data, and relative permeability plot for borehole FL-801 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Figure 7. Diagram showing geophysical logs, televiewer image, heat-pulse flowmeter data, and relative permeability plot for borehole FL-802 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Figure 8. Diagram showing attenuation tomagram (a) and velocity tomagram (b) from cross-borehole radar data collected between boreholes FL-800 and FL-802 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Figure 9. Diagram showing piper diagrams showing hydrogeochemical classification of water from selected intervals of borehole FL-800 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Figure 10. Diagram showing selected hydrogeologic features at boreholes Fl-800, FL-801, and FL-802 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Figure 11. Plot showing slug test data collected from interval C of borehole FL-800 at the study site in the vicinity of Waupun, Fond du Lac County, Wis., and estimated horizontal hydraulic conductivity using Hvorslev equation.

Figure 12. Plot showing changes in water levels observed in interval J during multiple-well constant-discharge aquifer tests at the study site in the vicinity of Waupun, Fond du Lac County, Wis.: (a) well is FL-800, (b) well is FL-801, (c) well is FL-802.

Figure 13. Plot showing changes in water levels observed in interval K during multiple-well constant-discharge aquifer tests at the study site in the vicinity of Waupun, Fond du Lac County, Wis.: (a) well is FL-800, (b) well is FL-801, (c) well is FL-802.

Figure 14. Plot showing multiple-well constant-discharge data collected from interval J of borehole FL-801 during pumping of borehole FL-800 at the study site in the vicinity of Waupun, Fond du Lac County, Wis., and estimated transmissivity and horizontal hydraulic conductivity using the Cooper and Jacob equation.

Tables

Table 1. Diagram showing regional stratigraphy of southern and eastern Wis.

Table 2. Abbreviated lithologic description and stratigraphic interpretation by Illinois State Geological Survey of core from borehole FL-800 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Table 3. Physical properties of selected rock core intervals in borehole FL-800 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Table 4. Results of analyses for trace elements, major ions, and physical properties in water samples collected from intervals F, E, D, and C in borehole FL-800 on April 24 and 25, 1996, at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Table 5. Results of analyses for inorganic constituents in water samples collected from intervals F, E, D, and C in borehole FL-800 on April 24 and 25, 1996, at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Table 6. Results of analyses for organic compounds in water samples collected from borehole FL-800 during borehole development on April 8 and 9, 1996, and from intervals F, E, D, and C sampled on April 24 and 25, 1996 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Table 7. Single-hole ground-penetrating radar directional reflection survey indicating the strike directions, dips, and intersection with borehole of reflectors in borehole FL-800 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Table 8. Measured static water levels in selected intervals in boreholes FL-800, FL-801, and FL-802 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Table 9. Vertical hydraulic gradients calculated between selected intervals in boreholes FL-800, FL-801, and FL-802 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Table 10. Horizontal hydraulic conductivity of intervals in boreholes FL-800, FL-801, and FL-802 estimated from slug tests at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Table 11. Horizontal hydraulic conductivity of intervals in boreholes FL-800, FL-801, and FL-802 estimated from multiple-well constant-discharge aquifer tests at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Conversion Factors, Vertical Datum, and Abbreviated Water-Quality Units

Abstract

Three boreholes were drilled at a farm site near Waupun, Wis., to improve the understanding of regional hydrogeology of the Ordovician Sinnipee Group. At the site the Sinnipee Group is the uppermost bedrock unit and is found to be about 183 ft thick. On the basis of core descriptions by the Illinois State Geological Survey, the Sinnipee Group at the site comprises (stratigraphically lowest to highest) the Platteville Formation (about 51 ft thick), the Decorah Formation (about 14 ft thick), and the Galena Dolomite (about 119 ft thick). The Illinois State Geological Survey noted that hardgrounds were common in the rock core, some having stratigraphic significance. Four very well developed hardgrounds were identified, three of which were used as formation or member contacts. The hardground at about 797 ft NGVD 29 represents the top of the Platteville Formation, the hardground at about 754 ft represents the top of the Pecatonica Member of the Platteville Formation, and the hardground at about 746 ft represents the top of the Glenwood Formation.

On the basis of samples collected from one borehole, the ground water at the site is of the calcium-magnesium bicarbonate type. Trichloroethene was detected in one sample at a concentration of 1 µg/L, and the concentration of antimony in one sample exceeded the U.S. Environmental Protection Agency (USEPA) Primary Drinking Water Standard. Other water samples contained aluminum and sodium in concentrations that exceeded the USEPA Secondary Drinking Water Standard and the USEPA Drinking Water Equivalent Level, respectively. Samples from various depths contained concentrations of iron, manganese, or dissolved manganese that were near or exceeded the USEPA Secondary Drinking Water Standard.

The cross-borehole radar tomography data show differences in velocity and attenuation among the three major units in the Sinnipee Group. Matrix porosity measured in rock-core samples correlates well with these velocity and attenuation tomograms. The Galena Dolomite has the lowest mean porosity at 2.4 percent (7 samples) and is represented in the tomograms as generally having the lowest attenuation and greatest velocity. Below the Galena Dolomite is a transition to a zone with the greatest attenuation and lowest velocity on the tomograms. The rock core shows this interval to be the shaley dolomite of the Decorah Formation which has a mean porosity of 8.3 percent (2 samples). Below the Decorah Formation, the Platteville Formation has a mean porosity of 3.6 percent (6 samples) and is represented in the tomograms as having velocity and attenuation generally intermediate between the Galena Dolomite and the Decorah Formation. The evaluation of the single-hole directional ground-penetrating radar reflection survey in FL-800 identified 15 reflectors (secondary permeability features). Some of the reflectors do correlate with fractures and partings noted on geophysical logs and rock core; however, many additional fractures and partings identified by the televiewer log and/or core description were not measured by the borehole radar survey. Horizontal or sub-horizontal reflectors (bedding-plane partings) which do correlate with indications of bedding-plane partings on the acoustic televiewer intersect the borehole at about 917 ft, 907 ft, 870 ft, 805 ft, and 797 ft.

The flowmeter profiles indicate that water entering and exiting the boreholes at seven bedding-plane partings accounts for most of the total borehole transmissivity. The flowmeter profiles in all three boreholes show that more than 90 percent of the total borehole transmissivity is provided by bedding-plane partings found at 870 ft and higher—stratigraphically within the Galena Dolomite. Static water levels were measured in selected intervals of the three boreholes, and vertical hydraulic gradients were estimated by comparing levels in adjacent intervals. Gradients were found to be almost uniformly downward, ranging from -0.040 to -1.251 ft/ft. On the basis of displacement recovery tests, estimates of horizontal hydraulic conductivity for the isolated intervals in the three boreholes ranged from 0.3 to 61 ft/d. Intervals that included partings had estimated conductivities over the entire range from 0.3 to 61 ft/d; intervals that were primarily rock matrix had estimated conductivities ranging from 0.4 to 5 ft/d. Two intervals were selected for multiple-well constant-discharge testing on the basis of evaluation of the core and geophysical logs, and the relatively high permeability exhibited by displacement/recovery tests. These intervals are within the Galena Dolomite and contain bedding-plane partings that appear to be present in all three boreholes. Multiple-well constant-discharge tests were conducted for each interval independently. The hydraulic conductivity for the stratigraphically higher interval (about 863 to 877 ft) ranged from about 94 to 201 ft/d. This conductivity was consistently greater than that estimated for the stratigraphically lower interval (about 803 to 817 ft) which ranged from 7 to 9 ft/d. During the constant-discharge multiple-well testing of these intervals, a greater hydraulic response was observed between boreholes aligned in a southeastern direction. A lower hydraulic response was observed between boreholes aligned in a northeastern direction, roughly orthogonal to the orientation of greater response.

Introduction

Most private wells and some municipal-water-supply systems in the vicinity of Waupun, Wis., withdraw water from the Ordovician Sinnipee Group bedrock aquifer (Brown and others, 2000). Ground water in the Sinnipee Group aquifer is generally susceptible to contamination because it is near land surface over much of the study area, and secondary permeability in the form of fractures and bedding-plane partings allow rapid movement of water, providing limited capacity to attenuate contaminants (Brown and others, 2000). Because of this susceptibility to contamination, a better understanding of the hydrogeologic characteristics of the Sinnipee Group aquifer would be very useful in managing and protecting this ground-water supply.

In 1995, the U.S. Geological Survey (USGS), in cooperation with the U.S. Environmental Protection Agency (USEPA), began a hydrogeologic study of the Ordovician Sinnipee Group at a farm site located 4.3 miles north of Waupun, in Fond du Lac County, Wisconsin (fig. 1). Data were collected from three boreholes at the study site to support an ongoing effort by the USEPA and USGS to characterize the hydrogeology of the Sinnipee Group in Wisconsin and the stratigraphically equivalent Galena and Platteville Groups in Illinois. The site north of Waupun was chosen because of its location between previously investigated study sites to the south in northern Illinois and to the north in De Pere, Wisconsin (Batten and others, 1999; Kay and others, 2000).

Figure 1. Location of study site in the vicinity of Waupun, Fond du Lac County, Wis.

The study, which began in October 1995 with the drilling of three boreholes (FL-800, FL-801, and FL-802), and concluded in July 1997 with their abandonment, comprised six principal efforts: (1) collection and description of rock core, (2) geophysical logging using conventional techniques, (3) collection of static water-level measurements, (4) aquifer testing, (5) geophysical logging using ground-penetrating radar for single-borehole directional reflection surveys and cross-borehole tomography, and (6) water-quality sampling and analysis.

Purpose and Scope

This report presents the hydrogeologic properties that were found to be characteristic of the Sinnipee Group near Waupun, Wis., along with water-quality data for seven samples collected from the boreholes on April 8, and May 24 and 25, 1996. This report provides details on the drilling and coring of three boreholes, as well as borehole geophysical data, a description of the rock core, lithostratigraphic interpretation, and density and matrix porosity measurements of 17 core samples. Also discussed is the vertical distribution of static water levels measured in 11 packed intervals and the vertical gradients calculated from those water-level measurements. In addition, this report presents the vertical distribution of estimated horizontal hydraulic conductivity based on displacement/recovery tests and multiple-well constant-discharge aquifer tests.

Description of Study Area

The study site lies within the Eastern Ridges and Lowlands Geographic Province of Wisconsin (not shown) as defined by Martin (1965). Topography within this province is generally flat to gently rolling, typified by the presence of numerous marshlands. The most prominent topographic feature in Fond du Lac County is a generally northeast-trending dolomite ridge, the Niagarian Escarpment, which is exposed approximately 10 miles east of the site (fig. 1).

In southern and eastern Wisconsin, crystalline rocks of the Proterozoic and Archean Eons underlie sedimentary rocks of Cambrian through Devonian Periods (table 1). The sedimentary bedrock dips gently to the east and southeast into the Michigan Basin. The Ordovician Galena-Platteville bedrock unit is identified as the Sinnipee Group in Wisconsin, and as the Galena and Platteville Groups in Illinois (Brown and others, 2000). The Sinnipee Group is considered a confining unit in those areas where it is overlain by other bedrock units; it is generally considered an aquifer where it is the uppermost bedrock unit (subcrop), as in most of northern Illinois and much of central and southern Wisconsin. The Sinnipee Group is predominantly dolomite, though with a greater proportion of limestone in some areas.

Table 1. Regional stratigraphy of southern and eastern Wisconsin (modified from Conlon, 1998).

In the eastern part of Fond du Lac County, the Ordovician Sinnipee Group is overlain by the younger Ordovician Maquoketa Shale and the Silurian Dolomite (Conlon, 1998). West of the Niagarian Escarpment (fig. 1) the Maquoketa Shale and Silurian Dolomite units are absent (Mudrey and others, 1982), and the Sinnipee Group is considered to be an aquifer. At the study site, the Sinnipee Group bedrock is overlain by a thin layer of unconsolidated deposits (less than 20 ft) of Quaternary age.

The study site falls within the Glaciated Paleozoic Hydrogeologic Province of Wisconsin (Zaporozec and Cotter, 1985). Within this province, the site is in the Eastern Drift Hydrogeologic District, which is characterized as a thick, multilayered complex of productive water-bearing Paleozoic sandstone and dolomite with interbedded resistive layers, locally overlain by productive water-bearing sand and gravel.

Nearly all ground water in this area of the State originates as precipitation. Average annual precipitation is 30.15 in. based on data for 1971 to 2000 from the National Oceanic and Atmospheric Administration/National Weather Service Cooperative Observer Network Station at Fond du Lac (Coop Station ID 472839), located approximately 10 mi northeast of the study site (not shown) (Wisconsin State Climatologic Office, 2002). A small amount of recharge may be attributed to infiltration from streams and ponds (Newport, 1962). Ground water in the dolomites of the Sinnipee Group is recharged primarily by the direct downward percolation of precipitation through Quaternary deposits to the water table. As a result, the Sinnipee Group at the study site has likely been exposed to greater infiltration and dissolution than in areas to the east where younger bedrock units overlie it. The general direction of ground-water movement at the site is to the southeast, with a horizontal hydraulic gradient of about 10 to 20 ft per mile (Newport, 1962).

Methods of Study

Data collection at the study site involved construction and development of boreholes, rock coring, borehole geophysics, ground-penetrating radar, displacement/recovery and multiple-well constant-discharge aquifer tests, and water-quality sampling. The methods employed for collection of these data are discussed below.

Borehole Construction and Development

Three boreholes—identified as FL-800, FL-801, and FL-802—were drilled from October 13 through 19, 1995. FL-802 was drilled 82 ft to the southeast of FL-800 (fig. 2), and FL-801 was drilled 58 ft to the west of FL-802. The horizontal distance between FL-800 and FL-801 could not be measured directly because a building is located between the two boreholes. A surveying level was used to determine the angle created by the three boreholes and the distance between FL-800 and FL-801 was calculated to be about 70 ft.
The three boreholes were drilled using a Portadrill 524 air/mud rotary rig. The general drilling procedure used for each borehole follows.

1. Drill a nominal 9-7/8-in. borehole through approximately 16 ft of unconsolidated Quaternary deposits and about 3 ft into the top of the bedrock.
2. Set 6-in. steel casing in the borehole and fill the annulus with cement grout.
3. Drill a nominal 6-in. borehole to a total depth (TD) of 206 ft.

An exception to the above procedure was FL-800, which was cored from the bottom of the 6-in. casing to TD. The coring resulted in the recovery of 3-in. diameter rock core and left a borehole about 5-in. in diameter. Following completion of coring operations, the borehole was reamed to a nominal 6-in. diameter.

Figure 2. Approximate location of boreholes FL-800, FL-801, and FL-802, and monitoring wells at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

The top of casing of FL-800 was established as the site datum with an elevation of 950 ft above NGVD 29 using USGS topographic maps. Using a surveying level, the relative elevations of the top of casing of FL-801 and FL-802 were measured to be 952.00 ft and 950.10 ft respectively. The top of the casing of FL-800 was used as the datum for all geophysical logging and aquifer testing. The ground surface at FL-800 (estimated to be 949 ft) was the datum for the rock core.

Borehole development requires that water be pumped from the productive intervals of the borehole at sufficient rates and total volumes to overcome the effects of drilling. These three boreholes were developed on April 8 and 9, and May 23, 1996, by lowering an electric pump to the bottom of each borehole and pumping at a rate of about 30 gal/min for approximately 110 minutes. During development, each pumped borehole was monitored with pressure transducers and a data logger, as was each of the other boreholes and three existing monitoring wells, MW-1A, MW-1B, and MW-3B (fig. 2). Only FL-800 and FL-802 were developed during the first visit because an inflatable packer was stuck in FL-801 at about 60 ft of depth (890 ft above NGVD 29), preventing pump placement. The packer was recovered from FL-801 and the borehole was developed on May 23, 1996. FL-800 was developed a second time on May 23, 1996, because of low confidence in the drawdown data collected during the original development of the borehole.

Rock Core Evaluation

The rock core recovered from FL-800 was delivered to the Illinois State Geological Survey (ISGS) on February 7, 1996, for lithologic description and stratigraphic interpretation. The core was transferred to the USGS Illinois Water Science Center on March 21, 1996, for the determination of rock matrix properties of 17 samples of the core using methods described in Appendix A (Patrick Mills, U.S. Geological Survey, written commun., 1996); the specific matrix properties determined were porosity, grain density, and bulk density.

Borehole Geophysical Surveys

Natural gamma, short-normal resistivity, spontaneous potential, fluid resistivity, caliper, and acoustic televiewer tools, as well as a heat-pulse flowmeter, were run in all three boreholes on October 30 and 31, 1995. In addition, a neutron log was run in FL-800. Brief descriptions of these electric logging methods follow; however, Keys (1990) and Kay and others (2004) provide detailed explanations of the use of these logs in interpreting lithologic properties.

The natural gamma log records the amount of radiation emanating from naturally occurring sources in the rock, including uranium, thorium, and potassium. The amount of radiation emitted by most sedimentary rocks is related directly to the clay content.

Resistivity logs are electric logs that measure formation resistance to an electric current between an electrode on the tool moving up the borehole and an electrical ground at land surface. Generally, resistance to the imposed electric current decreases with increasing porosity, borehole diameter, fracture density, and concentration of dissolved solids in the water. For the short-normal resistivity tool, the spacing between the current-emitting and potential-measuring points is set at 16 in. As with other electric logs, the effectiveness of these logs is affected by vertical flow within a borehole that may obscure differences in the electrical resistivity and conductivity of the water.

The spontaneous potential (SP) log is an electric log that measures the natural differences in electrical potential between an electrode in the borehole and a reference electrode at land surface. SP logging can be done only in the uncased part of water- or mud-filled boreholes. Changes in SP voltage require the presence of water with differing chemical properties in the aquifer, a means of segregating these waters within the aquifer, and a point where the waters mix. SP logs can be used to identify primary and secondary permeability features in the borehole. Normal and SP resistivity logging can provide information on changes in lithology and water quality, indicating the presence of secondary permeability features.

The caliper log is a mechanical tool that measures the inside diameter of a borehole. Caliper logs can be run in cased or open holes, and in fluid- or air-filled holes. Changes in borehole diameter identified with the caliper logs can be associated with a variety of borehole features including fractures, washouts, solution openings, large vugs, and well casing and screens.

The neutron log is created by measuring the returning signal from a source that emits neutrons into the formation. The emitted neutrons interact with hydrogen in the formation; the amount of neutron energy adsorption is directly proportional to the hydrogen content. The hydrogen content is an indicator of water content, and by extension, formation porosity.

The acoustic televiewer scans the borehole with an acoustic beam generated by a rotating, rapidly pulsed piezometric source as the tool is moved through the borehole. The amplitude and traveltime of acoustic signals reflected from the wall are measured. A smooth, hard borehole wall produces a uniform acoustic reflection; the presence of a secondary porosity feature such as a fracture, a vuggy interval, or a solution feature in the borehole scatters the acoustic reflection, producing a dark feature on the televiewer image. In this way, televiewer images can be used to identify the type, apparent size, and orientation of secondary permeability features intercepting the uncased part of a borehole below the water table.

The heat-pulse flowmeter measures the velocity and direction of vertical flow at various depths in an uncased borehole. In a borehole of known diameter, water velocity can be converted to flow volume, which can be plotted to profile the vertical distribution of flow. Depth intervals where there are appreciable changes in the volume of flow between measurement stations are interpreted as intervals over which there is inflow to, or outflow from, the borehole. The amounts of water entering and exiting a borehole under any given hydraulic condition is proportional to the product of fracture permeability and the head difference driving the flow. A relative permeability profile can be obtained by subtracting flow rates in a borehole measured under two different head conditions. Ambient and steady injection were used as two different head conditions in evaluating the boreholes at the study site; the data were plotted as discrete flowmeter measurements (data) and as “step profiles” (interpretation) for each borehole (Paillet, 1998; Paillet, 2000).

Ground-Penetrating Radar Surveys

Ground-penetrating radar (GPR) uses the transmission and reflection of radar-frequency electromagnetic waves to detect variations in subsurface properties. GPR can be used in a single borehole for a directional reflection survey (transmitter and receiver in the same borehole) or in two boreholes for a cross-borehole GPR tomography survey (transmitter in one borehole and receiver in the other).

A single-borehole directional radar reflection survey was conducted in borehole FL-800 using a 60-MHz transmitter and a 60-MHz directional receiver. Single-borehole directional radar reflection surveys have been used to identify the location and orientation of radar reflectors that may be associated with secondary permeability features (including fractures) at distances of 10 to 100 ft from the borehole (Falk, 1992; Lane and others, 1994). The reflectors identified in the single-borehole survey can be compared to the interpretation of fractures provided by the acoustic televiewer.

A cross-borehole GPR tomography survey was conducted between boreholes FL-800 and FL-802. Cross-borehole GPR surveys measure the velocity and attenuation of the radar pulse between the two investigated boreholes. Cross-borehole tomography is the process by which a two-dimensional depiction of physical properties in the plane between two boreholes is made. For this survey, the transmitting antenna was placed in borehole FL-802 and the receiving antenna in FL-800. Many individual radar scans were made by positioning the receiver at regular intervals in the borehole. Variations in the velocity of the pulse through the dolomite were affected primarily by the presence of water-bearing porous matrix and fractures. Velocity data were used to calculate the porosity of the dolomite deposits between the two boreholes. Variations in the attenuation of the pulse are affected primarily by the mineralogy and competence of the rock. Areas of variation in the velocity and attenuation of the signal identified from the cross-borehole radar-tomography survey can be interpreted as lithologic boundaries or intervals of variation in primary or secondary porosity. Intervals of low signal velocity and high attenuation typically are associated with elevated porosity or high amounts of clay minerals.

The cross-borehole radar tomography survey between boreholes FL-800 and FL-802 was conducted using a 22-MHz transmitter. Data collected for the cross-borehole survey consisted of measurements at points in a 12.8 x 12.8 ft (4 x 4 m) grid from 26 ft to 180 ft below the top of casing (924 to 770 ft above NGVD 29), with “level-run” or common source-receiver data collected every 1.6 ft (0.5 m) from 19 ft (6 m) to 183 ft (57 m) between the boreholes. A more dense data set is usually desired for a cross-borehole survey, but site and equipment restrictions prevented the collection of these data. Vertical deviation logs are necessary to accurately determine the spatial locations of the transmitter and receiver in each borehole. Deviation logs, however, were not available for these boreholes, so for the analysis it was assumed that the boreholes do not depart from vertical. Tomograms were generated using TOMOCG (Ivansson, 1984; Day-Lewis and Lane, 2003), a PC-based inversion software provided by the RAMAC borehole-radar instrument manufacturer. Day-Lewis and Lane (2003) provide additional explanation on the use of cross-borehole radar tomography.

Aquifer Tests

Two types of hydraulic aquifer tests were conducted, displacement/recovery and multiple-well constant-discharge tests. The tests were performed on selected intervals (isolated using inflatable packers) in each of the boreholes. On the basis of inspection of the rock core from FL-800 and results of geophysical logging in all three boreholes, 11 intervals were selected for further evaluation in borehole FL-800 and 2 intervals in each of boreholes FL-801 and FL-802 (fig. 3). These intervals were chosen to evaluate the range of horizontal hydraulic conductivity (K) of the rock intersected by the borehole. The lithology of intervals chosen ranged from competent dolomite rock matrix to bedding-plane partings.

Figure 3. Intervals isolated by packers for boreholes FL-800, FL-801, and FL-802 at the study site in the vicinity of Waupun, Fond du Lac County, Wis. (Letters represent intervals selected for evaluation; datum for geophysical logs is top of casing; altitude at top of FL-800 casing is estimated to be 950 ft above NGVD 29; survey level measurement shows altitude of FL-801 is 952.00 ft; of FL-802 is 950.10 ft).

Displacement/Recovery Tests
Displacement/recovery tests (also called slug tests) are initiated by quickly lowering a solid cylinder (slug) below the water surface in a borehole causing the water level to quickly rise. The change in water level in the borehole due to the slug and the recovery of water level to a static level (falling-head test) were measured using a pressure transducer and recorded using a data logger. Slug tests were conducted using a 10-ft long solid polyvinyl chloride slug with a 0.625-in. radius. The riser pipe above the isolated intervals in which the slug was lowered had a 0.935-in. radius. Considering the volume of the riser pipe and the volume of the fully submerged slug, the initial rise in water level in the riser pipe was about 4.5 ft. All slug tests were conducted using the solid slug with the exception of those for intervals E and F in FL-800. Because the water column over the packed interval was insufficient, slugs of 1 and 2 gallons of distilled water were used for intervals E and F, respectively (fig. 3).

Displacement/recovery data were analyzed using the technique of Hvorslev (1951). This technique was developed for use in unconfined conditions and can be applied to boreholes that fully or partially penetrate a formation. The following conditions are assumed in the application of the Hvorslov technique:

1. Drawdown of the water table in the vicinity of the borehole during the test is negligible,
2. Unsaturated flow above the water table can be ignored,
3. Head losses as the water enters the borehole are negligible, and
4. The hydraulic unit is homogeneous and isotropic.

These conditions are likely to be met or approximated at the site boreholes over the small volume of rock affected by the tests.

The Hvorslev equation used in estimating K is

(1)

Where,

K = horizontal hydraulic conductivity,

r_c = effective radius of the well casing (0.078 feet for all tests),

r_w = effective radius of the well (0.25 feet for all tests),

L = length of isolated interval (varies by test), and

T_l = time required for the head increase in the well bore to dissipate.

Multiple-Well Constant-Discharge Tests
The hydraulic connection through specific permeable intervals between the three boreholes was evaluated by multiple-well constant-discharge aquifer tests in which water is pumped at a constant rate from one borehole, and changes in water level are observed in the pumped borehole and the other two. Packed intervals J and K were selected for multiple-well constant-discharge testing on the basis of evaluation of the core and geophysical logs, and the relatively high permeability exhibited by displacement/recovery test results. These intervals contain bedding-plane partings that appear to be present in all three boreholes. Multiple-well constant-discharge tests were conducted for each interval independently. To conduct the multiple-well constant-discharge test, the same permeable interval was isolated, using an inflatable packer above and below, in each of the three boreholes. Water was pumped from the isolated interval in one borehole at a constant rate using a down-hole Grundfos pump, and changes in water level were monitored in the isolated interval of all three boreholes. Changes in water levels above and below the packed intervals were also monitored. The pump was moved to a second borehole, and the interval was pumped again, with water-level responses monitored in all the boreholes. The pump then was moved to the third borehole, and the procedure was repeated. The rate of pumping during the tests was set at about 4 gal/min for interval K (maximum rate of the pump) and about 2 gal/min for interval J (maximum rate that would not cause drawdown below the pump).

The transmissivity (T) of intervals J and K in each well bore was estimated using the Cooper and Jacobs (1946) straight-line method:

(2)

Where,

T = transmissivity,

Q = well discharge, and

S_log = the measured rate of drawdown increase per common log cycle.

Estimated transmissivity was divided by the length of the isolated interval in the observed well to obtain an estimate of horizontal hydraulic conductivity.

Where,

K = horizontal hydraulic conductivity,

T = transmissivity, and

b = length of the isolated interval.

An example of recent application of Cooper and Jacob straight-line method to aquifer tests in Sinnipee Group rocks can be found in Kay and others (2000).

Water-Sample Collection

Water samples collected from FL-800 and FL-802 during borehole development on April 8 and 9, 1996, were submitted for analysis of organic constituents to the USEPA Region 5 Central Regional Laboratory in Chicago, Illinois. Water samples collected during aquifer testing of selected intervals on April 24 and 25, 1996, were submitted for analysis of organic and inorganic constituents to the USEPA Region 5 Central Regional Laboratory in Chicago, Illinois, and for analysis of inorganic constituents and major ions to the USGS National Laboratory in Denver, Colorado. Sampling and analytical procedures were consistent with those outlined in the sampling and analysis plan (U.S. Environmental Protection Agency and U.S. Geological Survey, 1996). Field water-quality parameters (pH, water temperature, specific electrical conductance, and redox potential) were collected using a flow-through-cell connected directly to the pump discharge.

Lithostratigraphy

On the basis of the detailed description of rock core provided by the ISGS using nomenclature consistent with Conlon (1998), borehole FL-800 intersects (from oldest to youngest) the Glenwood Formation of the Ordovician Ancell Group and the dolomites of the Ordovician Sinnipee Group (fig. 4). Approximately 3 ft of Glenwood Formation was recovered in the rock core and is described as a medium-grained, gray to brown sandstone. The Sinnipee Group at the site is about 183 ft thick and consists of light-gray to medium-bluish-gray dolomite. A detailed lithologic description of all these units is presented in table 2.

Figure 4. Generalized stratigraphy of the study site in the vicinity of Waupun, Fond du Lac County, Wis. (NGVD 29, National Geodetic Vertical Datum of 1929).

Table 2. Abbreviated lithologic description and stratigraphic interpretation by the Illinois State Geological Survey of core from borehole FL-800 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

[Modified from Michael L. Sargent and Zakaria Lasemi, Illinois State Geological Survey, written commun., 1997; full description is available upon request from U.S. Geological Survey; datum is ground surface, estimated to be 949.00 ft National Geodetic Vertical Datum of 1929 (NGVD 29); codes in parentheses are from the rock-color chart published by The Geological Society of America (1980)]

The Sinnipee Group comprises three units. From oldest to youngest they are the Platteville Formation, the Decorah Formation, and the Galena Dolomite. The Platteville Formation is about 51 ft thick and is massive dolomite that ranges in color from light brownish gray to very light pinkish gray. Three members are recognized in the Platteville Formation—Pecatonica, McGregor, and Quimby’s Mill Members. The top of the Platteville Formation is marked by a well-developed hardground, indicating the presence of an unconformity separating the Platteville Formation from the overlying Decorah Formation. The Decorah Formation is about 14 ft thick and composed of light gray to medium-light gray dolomite and shale. The dolomite to shale ratio of the Decorah Formation increases from 60:40 at its base to 95:5 at its top. The Galena Dolomite overlies the Decorah Formation and is about 119 ft thick. The Galena Dolomite comprises two members—the Dunleith Dolomite and Wise Lake Members—and is generally an argillaceous dolomite with a wide range of grayish colors, including light gray, pinkish gray, and yellowish gray. Upward-fining sequences are common, with some terminating in hardgrounds; shale partings are common as well.

Geophysical logs for the three boreholes indicate that the nature of the Sinnipee Group is similar over the relatively short distance between boreholes (figs. 5, 6, and 7). Therefore, the following comparisons between geophysical logs for borehole FL-800 (fig. 5) and the descriptions and physical analysis of the rock core can be extrapolated to the other two boreholes.

Figure 5. Geophysical logs, televiewer image, generalized core description, heat-pulse flowmeter data, and relative permeability plot for borehole FL-800 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Figure 6. Geophysical logs, televiewer image, heat-pulse flowmeter data, and relative permeability plot for borehole FL-801 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

Figure 7. Geophysical logs, televiewer image, heat-pulse flowmeter data, and relative permeability plot for borehole FL-802 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

In general, there is good correlation between the geophysical logs and the physical description of the core. For instance, the described shale content of the Decorah Formation (table 2) is reflected on the natural-gamma log (fig. 5) as a zone of high gamma counts per second between 796 and 810 ft. The Galena Dolomite and Platteville Formations, both described in core as more massive and less argillaceous, have relatively low gamma counts per second compared to the Decorah Formation. The shaley nature of the Decorah Formation also is reflected in lower resistance on the short-normal resistivity log (fig. 5).

Hydrogeological Characteristics

The hydrogeologic characteristics of the Sinnipee Group in the vicinity of Waupun are interpreted from the collected data. Measurement of rock-matrix properties provides a fundamental assessment of hydrogeological properties, the chemistry of water sampled from the boreholes reflects aquifer lithology, and comparison of the physical description of the rock core and geophysical data allows a broader interpretation of the local hydrogeologic characteristics of the Sinnipee Group.

Rock-Matrix Properties

Seven samples of the Galena Dolomite, two samples of the Decorah Formation, six samples of the Platteville Formation, and two samples of the Glenwood Formation were analyzed by hydrologists at the USGS Illinois Water Science Center for selected rock-matrix properties (table 3). The chosen samples did not have obvious development of secondary permeability. The greatest measured porosity is 14.6 percent in the Glenwood Formation; this porosity falls in the middle of the range of porosity for sandstones (Freeze and Cherry, 1979). Among the Sinnipee Group samples, porosity values ranged from 1.6 percent at the top of the Galena Dolomite to 9.7 percent in the Decorah Formation. The mean porosity of the two Decorah Formation samples is 8.3 percent, of the seven Galena Dolomite samples is about 2.4 percent, and of the six Platteville Formation samples is 3.6 percent. On the basis of this limited number of samples, it appears that the Decorah Formation has higher matrix porosity than either the Galena Dolomite or the Platteville Formation (table 3). The relatively low porosity of the Galena Dolomite and Platteville Formation appears due to the overall massive crystalline nature of the dolomites in these units.

Table 3. Physical properties of selected rock core intervals from borehole FL-800 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

[analyses conducted by the USGS Illinois Water Science Center; datum is land surface, estimated to be 949.00 feet above National Vertical Geodetic Datum of 1929 (NVGD 29)]

No substantial difference is apparent in either the bulk or grain densities in samples of the three Sinnipee Group units. Bulk density ranges from 2.4 to 2.8 g/cm³. Grain density ranges from 2.5 to 2.9 g/cm³ (table 3), the higher of which is a typical value for pure dolomite (Hurlbut and Klein, 1977, p. 308).

The higher measured porosity of the Decorah Formation compared to the rest of the Sinnipee Group (table 3) is reflected in the neutron-porosity log (fig. 5). The maximum neutron-porosity data (limestone calibration) indicate an apparent porosity of 10 to 20 percent in the shaley interval from 798 to 810 ft. Analysis of two core samples from the Decorah Formation provided porosity values of 6.9 and 9.7 percent. This is in contrast to the range of measured porosity of 1.6 to 4.3 percent for the rest of the Sinnipee Group. Assuming that pure shale would have an apparent porosity of about 30 percent (on the basis of log response in other areas), this means the maximum shale fraction is 30 to 60 percent, and probably averages 15 to 20 percent in this interval (Paillet and Crowder, 1996; Paillet, 1994). Neutron logging was performed in FL-800 only.

Except for the shaley interval from 798 to 810 ft mentioned above, the neutron log of borehole FL-800 (calibrated for limestone porosity) shows porosity values of -4 to -2 percent. Quartz lithology correction to neutron porosity logs gives about a +4 percent correction, whereas the dolomite lithology correction is about -5 percent for a nominal limestone calibrated value of 0. The small negative values for porosity in the -4 to 0 percent range indicate the presence of substantial quartz (possibly chert) in the dolomite (Paillet and Crowder, 1996; Paillet, 1994).

Radar-propagation velocity and radar-wave attenuation tomograms produced from the FL-800 to FL-802 cross-borehole data (figs. 8a and b) indicate the average velocity of 60-MHz radar waves at the site is about 305 feet per microsecond (95 meters per microsecond), and the average attenuation of radar waves is about 6.7 decibels per foot (21 decibels per meter). There is an inverse relation between velocity and attenuation at this site, consistent with the results of many other cross-borehole radar tomography studies. The decrease in radar-propagation velocity and the increase in radar-wave attenuation has been associated with, and is theoretically consistent with, increased water content and electomagnetic-wave attenuation due to the presence of high-porosity, electrically conductive rocks (Lane and others, 1994; Singha and others, 2000; Williams and Lane, 1998).

Figure 8. Attenuation tomagram (a) and velocity tomagram (b) from cross-borehole radar data collected between boreholes FL-800 and FL-802 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

The cross-borehole radar tomography data show differences in velocity and attenuation (fig. 8) among the three major units in the Sinnipee Group. Matrix porosity measured in rock-core samples (table 3) correlates well with these velocity and attenuation tomograms. The Galena Dolomite has the lowest mean porosity at 2.4 percent and is represented in the tomograms as generally having the lowest attenuation and greatest velocity. Below the Galena Dolomite is a transition to a zone with the greatest attenuation and lowest velocity on the tomogram (fig. 8). The rock core shows this interval (about 796 to 815 ft) to be the shaley dolomite of the Decorah Formation which has the greatest measured porosity of samples analyzed in the core—a mean porosity of 8.3 percent. Below the Decorah Formation, the Platteville Formation has a mean porosity of 3.6 percent and is represented in the tomograms as having velocity and attenuation generally intermediate between the Galena Dolomite and the Decorah Formation.

Two limitations were experienced with this cross-hole radar data collection. First, the density of the data was less than desired, limited as a result of logistical and equipment problems. Second, deviation logs were not run in boreholes FL-800 and FL-802, so borehole deviation is not known. Deviation information would provide more detail in locating the transmitter and receiver in each borehole. Assuming that boreholes are vertical usually is not a safe assumption, but the lack of deviation data does not appear to have an important effect on the interpretation in this case (John Lane, U.S. Geological Survey, written commun., 1999).

Water Type and Chemical Characteristics

Water-quality analyses were conducted for samples collected from FL-800 and FL-802. Samples were collected from both boreholes on April 8 and 9, 1996, immediately prior to the cessation of pumping during borehole development, and on April 24 and 25, 1996, from four packed intervals in FL-800 only. The intervals from shallowest to deepest are interval F (917 to 922.5 ft), interval E (905 to 907 ft), interval D (870 to 872 ft), and interval C (808 to 810 ft).

A single packer at 917 ft defined interval F, with the tested interval extending to the water table at 922.5 ft (fig. 3). When sampling interval F, the packed interval was pumped dry after approximately 18 minutes of pumping. The interval was allowed to recover for approximately 30 minutes, and then pumped again. Sample volumes recovered were sufficient for analysis of organic constituents and trace elements; however, the interval was pumped dry again with only enough water collected for analysis for some inorganic constituents. Therefore, interval F of borehole FL-800 could not be evaluated properly for water type.

The other sampled intervals, C, D, and E, were isolated by a packer on either side of a 2-foot screen. Intervals C and D are shorter packed intervals that fall within intervals J and K of FL-800, respectively (fig. 3). Results of analysis for inorganic constituents, trace elements, and major ions in samples collected from the four intervals are presented in tables 4 and 5; results for organic constituents are presented in table 6.

Table 4. Results of analyses for trace elements, major ions, and physical properties in water samples collected from intervals F, E, D, and C in borehole FL-800 on April 24 and 25, 1996, at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

[MCL, maximum contaminant level; - -, no established MCL; ­—, not analyzed; ND, not determined; mg/L, milligrams per liter; CaCO₃, calcium carbonate; µg/L, micrograms per liter; µS/cm, microsiemens per centimeter; °C, degrees Celsius; analyses were conducted by U.S. Geological Survey laboratory in Denver, Colo.; altitude of packed intervals defined in table 3; intervals depicted in figure 3]

  ^a Secondary Drinking Water Standard (U.S. Environmental Protection Agency, 2000).
  ^b For the purposes of this report, concentrations reported in milligrams per liter (mg/L) are equivalent to parts per million (ppm).

Table 5. Results of analyses for inorganic constituents in water samples collected from intervals F, E, D, and C in borehole FL-800 on April 24 and 25, 1996, at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

[all values reported in micrograms per liter; MCL, maximum contaminant level; --, no established MCL; <, less than the indicated detection limit; analyses were conducted by U.S. Environmental Protection Agency Central Regional Laboratory in Chicago, Illinois; altitude of packed intervals defined in table 4]

   ^a Secondary Drinking Water Standard (U.S. Environmental Protection Agency, 2000)
   ^b Primary Drinking Water Standard (U.S. Environmental Protection Agency, 2000)
   ^c Drinking Water Equivalent Level (U.S. Environmental Protection Agency, 2000)

Table 6. Results of analyses for organic compounds in water samples collected from borehole FL-800 during borehole development on April 8 and 9, 1996, and from intervals F, E, D, and C sampled during aquifer testing on April 24 and 25, 1996 at the study site in the vicinity of Waupun, Fond du Lac County, Wis.

[all values reported in micrograms per liter; MCL, maximum contaminant level; - -, no established MCL; <, less than detection limit; (J), estimated value; (B), detected in laboratory blank; —, not analyzed; altitudes of packed intervals defined in table 4; intervals depicted in figure 7; analyses were conducted by U.S. Environmental Protection Agency Central Regional Laboratory in Chicago, Illinois]