Attachment+5.pdf

Appendix I: XRI Report

M i s s o u r i R i v e r H y d r o g e o l o g i c I n v e s t i g a t i o n a n d I n t a k e C o n c e p t u a l D e s i g n S t u d y

Geophysical Investigation Missouri Riverbank Filtration System Bismarck, North Dakota

Prepared for:

CH2M Hill Engineers, Inc.

90 South Cascade Ave, Ste 700 Colorado Springs, CO, 80903

December 2014

December 16, 2014

Geophysical Investigation - Missouri Riverbank Filtration System, Bismarck, North Dakota

Prepared for:

CH2M Hill Engineers, Inc.

90 South Cascade Ave, Ste 700 Colorado Springs, CO, 80903

Submitted by:

Exploration Resources International Geophysics, LLC 6207 Hwy 80 East Vicksburg, MS 39180 Phone: (866) 974-6867

Todd Meglich, Project Manager, Geophysicist

Jared Abraham, Senior Research Geophysicist

The geophysical methods and field procedures described in this report are applicable to the particular project objectives, and these methods have been successfully applied by XRI to investigations of similar size and nature. However, field or subsurface conditions may differ from those anticipated, and the resultant data may not achieve the project objectives. XRI warrants that our services were performed within the limits prescribed by CH2M Hill Engineers, Inc., and with the usual thoroughness and competence of the geophysical profession. No other warranty or representation, either expressed or implied is included in this report. XRI conducted this project using the current standards of the geophysical industry and used in-house quality control standards to produce this geophysical survey.

Table of Contents 1 Introduction

1.1 Purpose of Project

1.2 Description of Project Area

1.3 Geophysical Methodology

1.3.1 Airborne Electromagnetics

1.3.1.1 AEM Instrumentation

1.3.1.2 AEM Data Acquisition

1.3.2 AEM Data Calibration and Quality Control

1.3.3 Direct-Current Electrical Resistivity

1.3.3.1 DC Resistivity Instrumentation

1.3.3.2 DC Resistivity Data Acquisition

2 Project Area Geology

2.1 General Description

2.2 Quaternary Deposits

2.3 Tertiary System

2.4 Cretaceous System

3 Hydrogeology

3.1 General Description

3.2 Surficial Aquifers

3.3 Bedrock Aquifers

4 Standard Data Processing

4.1 AEM Data Processing

4.1.1 Automatic Processing

4.1.2 Manual Processing and Laterally Constrained Inversions

4.1.3 Spatially Constrained Inversion

4.2 Magnetic Data Processing

4.3 DC Resistivity Processing

5 Data Interpretation

5.1 Overview

5.2 Painted Woods

5.3 Sundown Acres

5.4 Missouri River Correctional Center

5.5 Missouri River Corridor

5.6 Data Deliverables

6 Summary and Recommendations i XRI – Data Series Report: MRBFS Geophysical Surveys

Appendices Appendix 1 – SkyTEM Calibration Report

Appendix 2 – Large Format Interpretation Images

Appendix 3 – Metadata for Data Deliverables

Table of Figures Figure 1-1. MRBFS Geophysical survey area (yellow line) Figure 1-2. A graphic representation of the TEM method during airborne operations. A primary magnetic field is generated by the abrupt turn off of an electrical current in a transmitter loop. The primary field induces electrical currents in the subsurface (eddy currents) that vary in strength dependent on material properties. These eddy currents generate a secondary magnetic field that is detected by a receiver loop. Measuring changes of the secondary magnetic field with time allows for creation of a model of subsurface electrical resistivity Figure 1-3. Example conversion of a dB/dt sounding curve to a resistivity model through inversion for the TEM method. The left panel is a dB/dt curve recorded by an Rx coil with the use of a dual-moment Tx. The low moment is plotted in green and the high moment is plotted in red. The center panel is a table of the numerical results of inverting this dB/dt curve from material resistivity. The right panel shows a plot of the resistivity model with depth derived from this single TEM sounding Figure 1-4. Illustration of the SkyTEM 301 frame including instrumentation locations. The figure is positioned such as one would view the SkyTEM 301 frame from above, with the positive z axis positioned into the page. The dimensions are in feet Figure 1-5. Images of the SkyTEM 301 system: a) SkyTEM 301 system during production; b) front boom where most electronics are housed; and, c) frame, receiver tower, generator, and other electronics boxes Figure 1-6. Typical coverage of the AEM data along the river corridor Figure 1-7. Boundary Areas of processed AEM data (yellow polygons). Cultural features that resulted in loss of data are marked in red Figure 1-8. Common array configurations for DC surveys Figure 1-9. The ABEM Terrameter LS DC Resistivity system (top left). A planted electrode, jumper cable, and cable takeout (top right). Layout of the 6-cable, 21-takeout Terrameter LS (bottom) Figure 1-10. Locations of the DC resistivity survey lines Figure 2-1. Surficial geologic map of the project area including county lines (modified from Clay, 1980).

Figure 4-1. Example display of data inversion using Res2DINVx64 for Line 4. The top image shows the Apparent Resistivity data as calculated from the measured data. The middle image shows the Calculated apparent resistivity model that best fits the measured data. The bottom image shows the fInal 2D resistivity inversion result. Units in this image are in meters. Resistive features are shown in reds and oranges. Conductive features are shown in blues ii

Figure 5-1. CH2M Hill boring locations Figure 5-2. Geophysical data comparison at Painted Woods (DC Line 1). Top panel shows the DC resistivity acquired along the survey area and the bottom panel shows the AEM data closest to the DC survey line and borings. A location map is shown at top right. Lithology soil codes were transcribed from CH2M Hill boring logs. Resistive features (interpreted sands and gravels) are shown in reds and oranges. Conductive features (interpreted clays, mudstones, and/or shale) are shown in blues Figure 5-3. A zoomed perspective of the geophysical data with the screened interval marked at Boring

2. Top panel shows the DC resistivity acquired along the survey area and the bottom panel shows the AEM data closest to the DC survey line and borings. A location map is shown at top right. Lithology soil codes were transcribed from CH2M Hill boring logs. Resistive features (interpreted sands and gravels) are shown in reds and oranges. Conductive features (interpreted clays, mudstones, and/or shale) are shown in blues Figure 5-4. Interpretation of producing zone at Boring 2. The left panel shows the interpreted bedrock elevation in the area. The right panel shows the thickness of the interpreted producing zone based on the screened interval at Boring 2. The hatched area on the right panel indicates the extent of the resistive layer that overlays the producing zone at Boring 2 Figure 5-5. Geophysical data comparison at Sundance Acres (DC Line 2 and 4). Top panel shows the DC resistivity acquired along the survey area and the bottom panel shows the AEM data closest to the DC survey line and borings. A location map is shown at top right. Lithology soil codes were transcribed from CH2M Hill boring logs. Resistive features (interpreted sands and gravels) are shown in reds and oranges. Conductive features (interpreted clays, mudstones, and/or shale) are shown in blues Figure 5-6. Geophysical Data comparison at MRCC (DC Line 3). Top panel shows the DC resistivity acquired along the survey area and the bottom panel shows the AEM data closest to the DC survey line and borings. A location map is shown at top right. Lithology soil codes were transcribed from CH2M Hill boring logs. Resistive features (interpreted sands and gravels) are shown in reds and oranges.

Conductive features (interpreted clays, mudstones, and/or shale) are shown in blues Figure 5-7. Interpreted alluvial sediment thickness along the survey area. The left panel shows the sediment thickness in the northern area. The right panel shows the sediment thickness in the southern area. The gray line identifies the center of the Missouri River as traced from the 2014 NAIP imagery. .. 40 Figure 5-8. Interpreted thickness of resistive zones along the survey area greater than 50 ohm-m. The resistive zones have been color-shaded and then outlined in yellow. The interpreted sediment thickness is shown at 50% transparency. The gray line identifies the center of the Missouri River as traced from the 2014 NAIP imagery Figure 5-9. Six areas identified for future investigation along the survey area. Also included is the Interpreted thickness of resistive zones along the survey area greater than 50 ohm-m and the interpreted sediment thickness. The gray line identifies the center of the Missouri River as traced from the 2014 NAIP imagery

Table of Tables Table 1-1. Positions of instruments on the SkyTEM 301 frame, using the center of the frame as the origin in feet. Refer to Figure 1-4 for definition of the coordinate system and instrument locations Table 1-2. Positions of corners of the SkyTEM 301 transmitter coil, using the center of the frame as the origin in feet iii

Table 1-3. Locations of base station instruments Table 1-4. DC survey line summary Table 2-1. Generalized stratigraphic column showing units present within the project area (modified from Clayton, 1980 and Murphy et al., 2009) Table 5-1. Soil Descriptions from zones within Borings 1 and 2 that show same gradational variation in the electrical resistivity Table 5-2. General coordinates for location of areas identified for future investigation. Sites have not been assessed with regards to existing infrastructure, site feasibility, or site access

List of Abbreviations

1D One-dimensional 2D Two-dimensional 3D Three-dimensional A-m2 Ampere-square meter AEM Airborne Electromagnetic bgs below ground surface dB/dt change in amplitude of magnetic field with time DC direct-current DGPS Differential Global Positioning System ft feet ft2/d feet squared per day gpm gallons per minute HM high moment IGRF International Geomagnetic Reference Field LCI Laterally-Constrained Inversion LM low moment mg/l milligrams per liter MRBFS Missouri River Bank Filtration System MRCC Missouri River Correctional Center MRT Missouri River Trench NAD83 North American Datum of 1983 NAIP National Agriculture Imagery Program NAVD North American Vertical Datum PA Profile Analyst RBFS Riverbank Filtration System RMS root-mean-squared Rx receiver SCI Spatially-Constrained Inversion STD standard deviation TEM Transient Electromagnetic TDEM Time-Domain Electromagnetic (common term when referring to ground-based TEM) Tx transmitter USGS United States Geological Survey XRI Exploration Resources International iv

Executive Summary

Exploration Resources International (XRI) is pleased to submit this report to CH2M Hill Engineers, Inc.

(CH2M Hill) titled “Geophysical Investigation – Missouri River Bank Filtration System” (MRBFS). This project was initiated to collect airborne electromagnetic (AEM) and direct-current (DC) resistivity data along the Missouri River from the Garrison Dam to just south of Bismarck, in central North Dakota. The results presented here will assist with three-dimensional (3D) identification and location of the thickest sand/gravel sediments to aid in the location of drilling targets for the placement of a riverbank filtration system (RBFS). XRI entered into an agreement with CH2M Hill in October 2014 to conduct these geophysical surveys. The scope of work for this project was as follows:

• Acquire approximately 700 line-miles of AEM data along the Missouri River from Garrison Dam to south of Bismarck using the SkyTEM 301 Time-Domain AEM system;

• Acquire approximately 4.5 line miles of DC resistivity data at locations identified by CH2M Hill;

• Map(s) of interpreted depth-to-bedrock along the AEM cross sections;

• Map(s) of interpreted geologic materials and their relationship to current test holes and production groundwater wells (if available) along the AEM cross sections;

• Identification of potential test hole locations;

• All data and metadata files with maps presented in an attributed Google Earth file format and ESRI Arc file format; and,

• A report delivered in PDF digital format.

The DC ground-based data acquisition commenced on 14 October 2014 and was completed on 22 October 2014 with a total of 4.57 line miles of data acquired at 4 different locations. The AEM survey started on October 23rd and was completed on October 26th with a total of 735.5 line-miles of data acquired with the SkyTEM 301. AEM, magnetic Total Field, positioning (horizontal and vertical), and video data were collected during production flights.

The AEM data were processed to remove infrastructure (pipelines, power lines) that produces electromagnetic coupling within the AEM data. Data processing removed 55.2 line miles of data resulting in a total of 680.3 line-miles of AEM data. After final processing, AEM data inversions were conducted to transform the raw signals from the AEM system to a resistivity versus depth relationship.

Cutting-edge inversion techniques were used that incorporated calibrations, system positioning, and spatial constraints. These inversions produced a resistivity model (or virtual borehole) approximately every 75 feet (ft) along a flight line. The AEM and DC data were correlated with lithological information to produce a geologic framework interpretation for the project area.

The inverted AEM and DC data successfully identified the alluvial sediment – bedrock contact along the survey area. Based on the available lithologic boring data and using an 8-10 ohm-m value in the AEM data for the bedrock, alluvial sediment thicknesses range from 0 to 250+ ft along the river. The thicker sediment sections coincide with the old river channel visible in the AEM data. Interpretations of the geophysical data that coincide with CH2M Hill drilling operations and pump tests are also presented.

CH2M Hill drilled 14 borings at 3 locations (Painted Woods, Sundance Acres, and the Missouri River Corrections Center) and conducted 2 pump tests, Boring 2 at Painted Woods and Boring 7 at Sundance Acres. CH2M Hill reported preliminary pump rates of 800 gallons per minute (gpm) at Boring 2 and 420 gpm at Boring 7 during a 96-hour pump test. Examination of the AEM data near Boring 2 indicates bedrock in the range of 60 to 95 ft below ground surface (bgs) and that geologic materials similar to the screened interval in Boring 2 are interpreted to extend north past Boring 1A and almost to Boring 1. The thickness of this producing zone is interpreted to range from 10 to 25 ft. A slightly more resistive feature overlies this producing zone and also extends to north toward Boring 1. Interpreted bedrock elevations from the AEM data range from approximately 1,550 to 1,570 ft in the area. Additional work is recommended in this area to verify that similar pump rates of the 800 gpm could be obtained north of Boring 2. There were no unique features identified in the geophysical data sets near Boring 7 to indicate similar production rates, either greater than or less than 420 gpm, could be obtained within the Sundance Acres area.

In addition, six locations are identified for future investigation based on interpreted alluvial sediment thickness, sediment resistivities, and location. Common to each recommended site is alluvial sediment thickness in excess of 160 ft present in the old river channel. At each site, the old river channel intersects the existing bank allowing for the possibility of a preferential flow path. Also identified are resistive features greater than 50 ohm-m that are interpreted to be sand/gravel layers. Although the composition of these resistive features is unknown currently as none of the 14 borings intersected this feature, they might also offer a preferential flow path from the river.

1 Introduction

1.1 Purpose of Project

Effective water resource management requires knowledge of the location, amount, and quality of that resource. Geophysical surveys and in particular AEM surveys, flown with either helicopter or fixed-wing aircraft, have been increasingly employed to characterize aquifers and their geologic setting (Fitterman and Deszcz-Pan, 1998; Wynn, 2002; Jørgensen et al., 2003; Paine and Minty, 2005; Møller et al., 2009;

Viezzoli et al., 2010; Abraham et al., 2011a; Abraham et al., 2011b; Jørgensen et al., 2012; Oldenborger et al., 2013; Lawrie et al., 2012). The results of these surveys, presented as models of subsurface electrical resistivity, are combined with information on area geology, stratigraphy, and hydrology to produce an integrated model of the hydrogeologic framework for the area.

An AEM survey provides nearly continuous electromagnetic data. It is acquired quickly without trespass onto private property and can cover a very large area at a fraction of the cost associated with traditional ground-based data acquisition. Once acquired, AEM data can then be interpreted with additional information about an area such as ground based geophysical surveys, geophysical borehole logs, hydrogeologic data, and borehole lithology.

North Dakota state agencies are conducting a feasibility study pertaining to the ability to extract water through a riverbank filtration system (RBFS) from the Missouri River. The study is being conducted along the Missouri River and stretches from the Garrison Dam to approximately 7 miles south of Bismarck.

The purpose of the geophysical surveys is to help identify areas where sediment thickness is greatest (deeper depth to bedrock) and to potentially identify areas of geologic materials (coarse sands and gravels) capable of supporting the RBFS.

1.2 Description of Project Area

At 2,540 miles in length, the Missouri River is the longest river in the United States and is second only to the Mississippi River in the calculated drainage area 529,000 miles2 (Kammerer, 1990) in the United States. The project area for this work follows the Missouri River from the Garrison Dam (approximately 11 miles south of Garrison, ND) to just south of Bismarck, ND (Figure 1-1). This stretch of the Missouri River meanders approximately 72 miles down to the Bismarck/Mandan area from Garrison Dam. The project area then continues on for another 11 meandering linear miles south of Bismarck for a project total of 83 miles along the river. The Missouri River gently drops from an elevation of approximately 1,680 feet at the Garrison Dam to approximately 1,640 feet at the southern end of the survey area.

All aerial imagery used throughout this report is the 2014 imagery available through National Agriculture Imagery Program (NAIP).

FIGURE 1-1. MRBFS GEOPHYSICAL SURVEY AREA (YELLOW LINE).

1.3 Geophysical Methodology

Airborne and ground-based geophysical datasets were acquired for this project. The airborne data used the time-domain electromagnetic (TDEM) method while the direct-current (DC) resistivity method was used to acquire the ground-based data. Each method is discussed in detail below.

1.3.1 Airborne Electromagnetics

Transient Electromagnetic (TEM) surveys, whether done on the ground (Time-Domain Electromagnetic, TDEM) or from the air (AEM), provide characterization of electrical properties of earth materials from within a few feet of the surface down to depths of hundreds or even thousands of feet. The electrical properties of the subsurface are controlled by the material composition of the geology including the amount of mineralogical clay, the water content, the amount of dissolved solids, the metallic mineralization, and the percentage of void space. The TEM technique has been widely used for mineral exploration for decades, as it is sensitive to conductive features like metallic ore bodies. Conductivity is the reciprocal of resistivity. Advancements in acquisition electronics and computing processing power have made the TEM technique useful for near-surface geotechnical applications.

The TEM technique images the subsurface using electromagnetic induction. A primary transmitted current induces a secondary subsurface electrical current/magnetic field, and receivers measure this secondary magnetic field as the induced current dissipates into the ground with time and depth. The rate of dissipation of the electrical current in the subsurface is a function of the electrical resistivity of the materials through which the current passes. Figure 1-3 gives a conceptual illustration of the TEM method when deployed from the air.

To collect TEM data, an electrical current is generated within a transmitter (Tx) coil, usually a large loop of wire, possibly consisting of multiple turns. This current is switched off as abruptly as possible. At the moment of turn-off, a secondary current is generated within the subsurface immediately under the transmitter coil. The current dissipates and decays with time traveling deeper into the subsurface and spreads wider with depth. The rate of dissipation or diffusion is dependent on the electrical properties of the subsurface. The decaying secondary current generates a magnetic field, which in turn generates a current in a receiver (Rx) coil. This current is measured at several different moments in time (time gates). From this current, the rate of decay of the magnetic field (dB/dt) is determined. Each TEM reading results in a mapping of the change in magnetic field in the subsurface with time (the dB/dt).

When compiled, these measurements produce a plot of dB/dt vs. time, which becomes a sounding at that location. Each TEM measurement produces an electrical sounding for one point on the surface.

The sounding curves are numerically inverted to produce a model of subsurface earth resistivity values as a function of depth. Inversion relates the measured geophysical data to a probable source model of physical earth properties through mathematical iteration and physics. The inverted sounding curves produce an earth model of the resistivity of the subsurface. Figure 1-4 shows an example of a dual-moment TEM dB/dt sounding curve and the corresponding inverted electrical resistivity model.

FIGURE 1-2. A GRAPHIC REPRESENTATION OF THE TEM METHOD DURING AIRBORNE OPERATIONS. A PRIMARY MAGNETIC FIELD IS GENERATED BY THE ABRUPT TURN-OFF OF AN ELECTRICAL CURRENT IN A TRANSMITTER LOOP. THE PRIMARY FIELD INDUCES ELECTRICAL CURRENTS IN THE SUBSURFACE (EDDY CURRENTS) THAT VARY IN STRENGTH DEPENDENT ON MATERIAL PROPERTIES. THESE EDDY CURRENTS GENERATE A SECONDARY MAGNETIC FIELD THAT IS DETECTED BY A RECEIVER LOOP. MEASURING CHANGES OF THE SECONDARY MAGNETIC FIELD WITH TIME ALLOWS FOR CREATION OF A MODEL OF SUBSURFACE ELECTRICAL RESISTIVITY.

FIGURE 1-3. EXAMPLE CONVERSION OF A DB/DT SOUNDING CURVE TO A RESISTIVITY MODEL THROUGH INVERSION FOR THE TEM METHOD.

THE LEFT PANEL IS A DB/DT CURVE RECORDED BY AN RX COIL WITH THE USE OF A DUAL-MOMENT TX. THE LOW MOMENT IS PLOTTED IN GREEN AND THE HIGH MOMENT IS PLOTTED IN RED. THE CENTER PANEL IS A TABLE OF THE NUMERICAL RESULTS OF INVERTING THIS DB/DT CURVE FROM MATERIAL RESISTIVITY. THE RIGHT PANEL SHOWS A PLOT OF THE RESISTIVITY MODEL WITH DEPTH DERIVED FROM THIS

SINGLE TEM SOUNDING.

1.3.1.1 AEM Instrumentation

AEM data were acquired using the SkyTEM 301 AEM system. The SkyTEM 301 is a rigid frame TEM system that employs the patented MultiMoment® technology (SkyTEM, 2014). The MultiMoment® technology uses two different transmitter dipole moments that improve the resolution of near-surface features (the low moment) while maintaining good depth of investigation (the high moment). The transmitter dipole moment is the product of the electric current (Amperes A) passing through the Tx coil, the area of the Tx coil (in m2), and the number of turns of wire in the Tx coil. In the case of the SkyTEM 301, the area of the Tx coil is approximately 3,649 ft2 (339 m2) and the coil contains a single turn of wire. A peak current of approximately 7 A is passed through the Tx wire for low moment (LM) measurements, and a peak current of approximately 97 A is passed through the Tx wire for high moment (HM) measurements. This results in peak Tx low and high moments of ~2,030 Ampere-Square Meter (A-m2) and ~32,880 A-m2, respectively.

The SkyTEM 301 system places the Rx in a null position, which is slightly above and outside the Tx loop.

The null position is a spatial location where the intensity of the primary field from the system transmitter is negligible allowing maximum gain of the Rx to the secondary fields. The SkyTEM 301 multi-turn Rx coil has an effective area of 1,130 ft2. In addition to the Tx and Rx that constitute the TEM instrument, the SkyTEM 301 is also equipped with a total field magnetometer and data acquisition systems for both of these instruments. The SkyTEM 301 also includes two each of laser altimeters, inclinometers/tilt meters, and differential global positioning system (DGPS) receivers. Positional data from the frame mounted DGPS receivers are recorded by the TDEM data acquisition system. The magnetometer makes use of a third GPS receiver to time stamp the magnetic data. Figure 1-4 gives a simple illustration of the SkyTEM 301 frame and instrument locations. The image is viewed along the +z axis looking at the horizontal x-y plane. The axes for the image are labeled with distance in feet. The magnetometer is located on a boom off the front of the frame (right side of image). The Tx coil is attached to the octagonal frame and the Rx Coil is located at the back of the frame (left side of image).

The SkyTEM 301 was flown at an average speed of 50 mi/hour at an average flight height of 157 ft using the sling-load cargo system of an AS350 FX2 helicopter. Figure 1-5 displays a few pictures of SkyTEM 301 while on the ground and in operation.

The airborne coordinate system used defines the +x direction as the direction of flight, the +y direction is defined 90° to the right, and the +z direction is downward. The center of the transmitter loop, mounted to the octagonal SkyTEM frame is used as the origin in reference to instrumentation positions.

Table 1-1 lists the positions of the instruments (in feet), and Table 1-2 lists the corners of the transmitter loop.

FIGURE 1-4. ILLUSTRATION OF THE SKYTEM 301 FRAME INCLUDING INSTRUMENTATION LOCATIONS. THE FIGURE IS POSITIONED SUCH AS ONE WOULD VIEW THE SKYTEM 301 FRAME FROM ABOVE, WITH THE POSITIVE Z AXIS POSITIONED INTO THE PAGE. THE DIMENSIONS ARE

IN FEET.

FIGURE 1-5. IMAGES OF THE SKYTEM 301 SYSTEM: A) SKYTEM 301 SYSTEM DURING PRODUCTION; B) FRONT BOOM WHERE MOST ELECTRONICS ARE HOUSED; AND, C) FRAME, RECEIVER TOWER, GENERATOR, AND OTHER ELECTRONICS BOXES.

TABLE 1-1. POSITIONS OF INSTRUMENTS ON THE SKYTEM 301 FRAME, USING THE CENTER OF THE FRAME AS THE ORIGIN IN FEET. REFER TO

FIGURE 1-4 FOR DEFINITION OF THE COORDINATE SYSTEM AND INSTRUMENT LOCATIONS.

Instrument DGPS

DGPS

Inclinometer

Inclinometer

Altimeter

Altimeter

MAG

Sensor Rx Coil

X 38.3 34.5 42.0 42.0 42.5 42.5 60.3 -43.5 Y 9.2 13.0 5.4 5.4 5.9 -5.9 0.0 0.0 Z -0.5 -0.5 -0.4 -0.4 -0.4 -0.4 -1.8 -6.6

TABLE 1-2. POSITIONS OF CORNERS OF THE SKYTEM 301 TRANSMITTER COIL, USING THE CENTER OF THE FRAME AS THE ORIGIN IN FEET.

Tx Corners 1 2 3 4 5 6 7 8 X 37.2 19.8 -19.8 -41.2 -41.2 -19.8 19.8 37.2 Y 10.8 28.3 28.3 6.8 -6.8 -28.3 -28.3 -10.8

The DGPS and magnetometer mounted on the frame of the SkyTEM 301 require the use of base stations that are located on the ground while AEM data is being acquired. The DGPS base station records raw positional data so that the positional data recorded with the frame-mounted DGPS may be post-processed if required. The magnetometer base station recorded the daily variation of the Earth’s a)

b) c) magnetic field and is used to diurnally correct the magnetic total field data recorded by the magnetometer on the 301 frame. The base stations were positioned in an area with low cultural noise.

Data from the magnetometer and DGPS base stations were downloaded each day after the end of the day’s AEM flights. The DGPS and magnetometer base stations were located at the Washburn Municipal Airport at the coordinates listed in Table 1-3. The horizontal geodetic reference used for this project is the North American Datum of 1983 (NAD83) and State Plane North Dakota South Zone projection with the unit of measurement in feet. All elevations are from the United States Geological Survey (USGS) National Elevation Dataset, referenced to the North American Vertical Datum (NAVD) of 1988; the unit of measurement is in feet.

TABLE 1-3. LOCATIONS OF BASE STATION INSTRUMENTS.

Instrument Easting (ft) Northing (ft) Elevation (ft)

Magnetometer Base Station 1838162.4 17211809.4 1904 DGPS Base Station 1836340.3 17211793.9 1907

1.3.1.2 AEM Data Acquisition

Airborne data were collected along the survey area from 23 October 2014 – 26 October 2014 totaling approximately 735.5 line-miles. The airborne flight operations used the Mandan Municipal Airport and Washburn Municipal Airport for refueling and staging purposes. The data were acquired following the path of the river. In most places the pilot was able to acquire three survey lines over the river and three survey lines on each bank. Data were to be acquired out to 1,000 ft of the riverbank or as close to this as the helicopter pilot could safely manage and maintain proper system orientation. Figure 1-6 shows an example of the data coverage after removal of bad data (coupling, altitude, etc.) indicated by gaps in the flight lines. The gray-shaded area in Figure 1-6 shows a 1,000-foot buffer onto each bank when taking the river width into account. In most cases along the river the pilot was able to acquire most of the bank and in some cases exceeded the 1,000-foot coverage. The average width of the data acquisition was approximately 4,050 ft along the river (including the river width). Figure 1-7 shows the areas of data that were free of cultural interference used to create the final inverted dataset. AEM data were not acquired near the Bismarck/Mandan area due to flight restrictions under Federal Aviation Authority regulations and the significant number of cultural features in the area.

FIGURE 1-6. TYPICAL COVERAGE OF THE AEM DATA ALONG THE RIVER CORRIDOR.

FIGURE 1-7. BOUNDARY AREAS OF PROCESSED AEM DATA (YELLOW POLYGONS). CULTURAL FEATURES THAT RESULTED IN LOSS OF DATA

ARE MARKED IN RED.

1.3.2 AEM Data Calibration and Quality Control

All SkyTEM systems are calibrated to a ground test site in Lyngby, Denmark prior to being used for production work (HGG, 2010; HGG, 2011; Foged et al., 2013). The calibration process involves acquiring data with the system while hovering at different altitudes from 16 to 150 ft over the Lyngby site.

Acquired data are processed, and a scale factor (time and amplitude) is applied so that the inversion process produces the model that approximates the known geology at Lyngby.

Upon installation of the navigational instruments in the helicopter and assembly of the SkyTEM 301 system, several test flights were flown to ensure that the equipment was operating within technical specifications. Initial survey set-up procedures include measurement of the transmitter waveforms, verification that the receiver is properly located in a null position, and that all positioning instruments (DGPS’s, altimeters, inclinometers) are properly functioning. High altitude tests, used to verify system performance, are flown once at the beginning of the survey and repeated throughout the survey. In the field, visual quality control of the EM and magnetic operational parameters including current levels, positioning sensor dropouts, acquisition speed, and system orientation is conducted with proprietary SkyTEM software following each flight.

1.3.3 Direct-Current Electrical Resistivity

The DC resistivity method measures the bulk resistance of earth materials to the passage of electricity. This property is dependent on the resistivity (i.e. quality) of the pore water, the quantity of pore water (an indicator of porosity), the resistivity of the grains, and the presence of clay materials in the matrix. Resistivity surveys are used to identify areas of low or high resistivity that might indicate increased clay content or higher salinity (low resistivity) or fresh water content (high resistivity – i.e. sand/gravel layers).

Resistivity data offers a high degree of vertical and lateral resolution of the subsurface electrical variations. By measuring the subsurface electrical properties, a cross-sectional or two-dimensional (2D) profile can be built.

These cross-sections typically plot the resistivity data as a function of along-line distance and depth.

The fundamental physical law used in resistivity surveys is Ohm’s Law, which governs the flow of current in the ground. In practice, what is measured is the electric potential (voltages). During acquisition, current is injected into the ground at one location (current electrode), and the voltages are measured at another location (potential electrode). From this data, an apparent resistivity is calculated (the resistivity of a homogenous half space that would produce the measured voltage). Inversion of the data produces models with “actual resistivity” distributions. While the relationship between geology and resistivity is non-unique, FIGURE 1-8. COMMON ARRAY

CONFIGURATIONS FOR DC SURVEYS

inferences can be made about the physical characteristics of the subsurface using empirical resistivity values for common lithologies.

DC resistivity surveys can be conducted using different configurations dependent upon the depth of investigation and target of interest. A common factor in these configurations is a set of current input electrodes usually labeled A and B and a set of voltage measurement electrodes usually labeled M and N. Figure 1-8 shows four common electrode arrays. The different configurations result in the arrays being sensitive to different features or to allow for a better efficiency in the data acquisition.

Schlumberger arrays tend to be more sensitive to vertical variations in the resistivity, while the Wenner array is more sensitive to lateral variations. At shallower depths, the Dipole-Dipole array provides good horizontal and lateral resolution and is well suited to multi-channel acquisition systems. For these surveys, an ABEM-designed gradient array was used that maximizes the efficiency of the 6-cable, 4-channel Terrameter LS system manufactured by ABEM (ABEM, 2012). The gradient array provides good horizontal and lateral resolution of the subsurface electrical resistivity variations while providing good depth of investigation.

1.3.3.1 DC Resistivity Instrumentation

The Terrameter LS (Figure 1-9) is a multifunctional data acquisition system capable of collecting resistivity, induced polarization, and self-potential geophysical measurements. The Terrameter used for these surveys had six electrode cables each with 21 takeouts, 16.4 ft (5 m) between each takeout, at which to connect stainless-steel electrodes (Figure 1-9) which make the direct contact with the ground.

Each cable overlaps the last takeout with the first takeout of the following cable, using 121 electrodes in total (Figure 1-9) and allowing for a maximum single line length of 1,968 ft (600 m). For survey lines longer than 1,968 ft, a technique called a “roll along” is used to extend data coverage. Data is typically acquired from the beginning of the survey line to the end of the cable extent in a systematic fashion. As data acquisition is completed on each of the cables, the cables and electrodes are picked up and moved to the end of the line and redeployed. Once all data acquisition on the 6-cable setup is complete, the Terrameter is typically moved up 1 cable length, and acquisition starts again on all 6-cables. By continually moving each cable to the end, survey lines can be extended to greater and greater lengths.

1.3.3.2 DC Resistivity Data Acquisition

A total of four DC resistivity lines were acquired using a gradient array (Figure 1-10). Line 1 used electrode spacings of 13.1 ft (4 m) and 16.4 ft (5 m), while Lines 2-4 used an electrode spacing of 16.4 ft (5 m). A single cable roll-along was used for the first 7,800 ft along Line 1. Analysis of the field data showed that the depth of investigation exceeded 300 ft, and it was determined that a 2-cable roll-along would provide depth of investigation in excess of 200 feet below the ground surface. The remaining 4,000 ft of Line 1 and all of Lines 2 and 3 used a 2-cable roll-along. Line 4 was only 1,312 ft in length and did not require a roll-along. Table 1-4 lists the details about the survey parameters for each line.

A Garmin RINO650 handheld GPS was used to survey the start and end of each cable along the survey line. Additionally, CH2M Hill boring locations were surveyed using the RINO650 as well as having the down-line linear distance of each boring noted by the field crew (e.g. Boring 1 was located at 195 ft from the start of cable along Line 1).

FIGURE 1-9. THE ABEM TERRAMETER LS DC RESISTIVITY SYSTEM (TOP LEFT). A PLANTED ELECTRODE, JUMPER CABLE, AND CABLE TAKEOUT

(TOP RIGHT). LAYOUT OF THE 6-CABLE, 21-TAKEOUT TERRAMETER LS (BOTTOM).

TABLE 1-4. DC SURVEY LINE SUMMARY

ID Location Total Length (ft) Electrode Spacing (ft)

Line 1 Painted Woods 11,876 13.1 and 16.4 Line 2 Sundance Acres 7,020 16.4 Line 3 Missouri River Correction Center (MRCC) 3,937 16.4 Line 4 Sundance Acres 1,312 16.4 Total Distance 24,145

FIGURE 1-10. LOCATIONS OF THE DC RESISTIVITY SURVEY LINES

2 Project Area Geology

2.1 General Description

The project area is situated within the Missouri River Trench (MRT) district in the Glaciated Missouri Plateau section of the Interior Plains Physiographic Province (Fenneman, 1931). The trench district includes the valley floor, which contains the present-day Missouri River channel, as well as several terraces formed from outwash, fluvial deposits, and exposed bedrock strata. Glacial deposits, primarily till and outwash, are present in the uplands east of the trench along the entire project area. However, within the trench, till is mostly absent except in isolated areas near Bismarck. The trench ranges in width from one to three miles. It has a maximum relief between the valley floor and the upland plateau of approximately 350 ft in McLean County. The alluvium within the valley floor consists of variably sorted sand and gravel, with minor silt and sandy clay that ranges in thickness from 100 to around 115

ft. Alluvium within and adjacent to the live channel of the Missouri River is comprised of meander and channel bar deposits that are modified over relatively short periods of time due to changes in river discharge and periodic floods (Kume and Hansen, 1965; Bluemle, 1971).

Underlying the unconsolidated deposits in the MRT in the project area is a several-thousand foot thick sequence of Tertiary- to Paleozoic-age sedimentary strata that dips northwestward toward the center of the Williston Basin. Some of the Tertiary intervals of this sequence are exposed along the valley walls of the MRT. Some strata in this sequence contain aquifers that support low to moderate yield wells. A stratigraphic column listing the major geologic units described in this report is shown in Table 2-1, and the distribution of surficial geology within the project area is displayed in Figure 2-1.

TABLE 2-1. GENERALIZED STRATIGRAPHIC COLUMN SHOWING UNITS PRESENT WITHIN THE PROJECT AREA (MODIFIED FROM CLAYTON, 1980 AND MURPHY ET AL., 2009).

Era System Series Group Formations Primary Composition and Maximum Thickness (ft)

Ce no zo ic

Quaternary Holocene Oahe clay, silt, sand, gravel (100)

Pleistocene Coleharbor “uncollapsed river sediment” (USGS) sand and gravel, clay, silt (100 in Missouri River Trench)

Tertiary Paleocene Fort Union

Sentinel Butte sandstone, siltstone, claystone, lignite, clinker (650)

Bullion Creek sandstone, siltstone, claystone, lignite, clinker (650)

Slope sandstone, siltstone, claystone, lignite, clinker (270)

Cannonball mudstone and sandstone (255)

M es oz oi c

Cretaceous

Upper

Montana Hell Creek sandstone, siltstone, claystone, lignite

(330)

Fox Hills mudstone, siltstone, sandstone

Colorado Niobrara, Carlile, Greenhorn, Belle Fourche

Alternating sequences of clastic and chemical/biochemical sedimentary deposits (each group exceeding 1,100 ft in thickness) Lower Dakota

Mowry, Newcastle, Skull Creek, Inyan Kara

FIGURE 2-1. SURFICIAL GEOLOGIC MAP OF THE PROJECT AREA INCLUDING COUNTY LINES (MODIFIED FROM CLAY, 1980).

2.2 Quaternary Deposits

The riverbed deposits beneath the present-day Missouri River and adjacent unconsolidated deposits in the MRT valley floor are part of the Holocene Oahe Formation. Clayton (1980) describes the Oahe Formation river sediments as “dark, obscurely bedded clay and silt (overbank sediment); generally overlying cross-bedded sand (channel sediment); as thick as 30 ft; on flood plains of modern streams.”

The sediment cores at the CH2M Hill’s borehole locations with brown and gray clay and silt with intervals of sand match this description closely. The Oahe Formation has three additional facies (windblown sand, loess, and pond deposits), but the river sediment deposits of the formation are the most extensive unit present in the project area. Sharing the MRT with the Oahe Formation are deposits of the Pleistocene/Holocene Coleharbor Formation. This unit, like the Oahe Formation, consists of several facies, many of which describe the extensive glacial deposits that mantle much of North Dakota to the north and east of the project area. Within the project area, the river sediment facies of the Coleharbor Formation is present along the valley edges of the MRT in strips ranging from less than a half mile to over two miles in width. The river sediment facies of the Coleharbor Formation are described as “moderately well sorted cross-bedded sand and plane-bedded gravel, including sediment of melt-water and other rivers, as thick as 100 ft. Flat-bedded sediment of gently sloping planes and terraces, commonly with braided channel scars” (Clayton, 1980). The river facies sediments were deposited by glacial meltwater during the Wisconsin stage of the Pleistocene Epoch, as well as by non-glacial rivers at the end of the Pleistocene and in early Holocene time (Bluemle, 1971).

The most extensive deposits of this unit are downstream of Garrison Dam on the east bank of the Missouri River, along the west bank of the Missouri River southwest of the town of Washburn, and along a seven mile long corridor of the MRT immediately north of the city of Bismarck, where the deposits fill the entire valley from the edge of the river channel to the MRT rim.

2.3 Tertiary System

In the project area, a sequence of marine and near-shore Tertiary sedimentary strata of the Fort Union Group is incised by the MRT, and several of these units are exposed at various locations along the valley walls or subcrop beneath unconsolidated colluvium, loess, or other detrital deposits (Clayton, 1980).

The Fort Union units present within and adjacent to the MRT area are described in descending order stratigraphically-

Sentinel Butte Formation- This formation is exposed along the valley walls and uplands between Garrison Dam and Washburn, with its most extensive exposure on the west side of the MRT for about 10 miles downstream of Lake Sakakawea. The unit is composed of silt, sand, clay sandstone, and lignite and can approach 600 ft in thickness. This unit is known as the primary coal producer in North Dakota (Clay, 1980; Murphy et al., 2009).

Bullion Creek Formation- This unit is also present along the MRT valley walls upstream of the town of Washburn, particularly along the stretch where the Missouri River flows west to east. The Bullion

Creek Formation is comprised of interlayered silt, sand, sandstone, clay/claystone, and lignite that reach a maximum thickness of 600 ft in North Dakota (Clay, 1980; Murphy et al., 2009).

Slope Formation- The Slope Formation is present along the west side of the MRT for a distance of approximately 15 miles downstream from the town of Washburn. The Slope Formation is similar in composition to the overlying Fort Union Group formations, but approaches a maximum thickness of 270 ft. The claystone and clay deposits erode to form steep slopes and form “badland” topography in southwest North Dakota (Clay, 1980; Murphy et al., 2009).

Cannonball Formation- Along most of the MRT from Bismarck to Washburn, the Eocene Cannonball Formation forms the valley walls and uplands immediately adjacent to the valley floor. The Cannonball Formation consists primarily of marine sandstone, shale, siltstone, and lenticular seams of limestone. Cross sections of the MRT north of Bismarck indicate the thickness of the Cannonball Formation can approach 400 ft (Kume and Hansen, 1965; Clayton, 1980; Murphy et al., 2009).

2.4 Cretaceous System

Underlying the Oahe Formation on the southern edge of the project area is the upper Cretaceous Hell Creek Formation that forms the consolidated basement of the MRT. This formation is also exposed in a limited extent on the west and east sides of the MRT south of the city of Mandan near the southern AEM survey flight lines. The Hell Creek Formation is composed of sandstone, mudstone, siltstone, carbonaceous shale, and thin intervals of lignite that are mostly of continental origin (Kume and Hansen, 1965). Immediately beneath the Hell Creek Formation is the Fox Hills Formation, composed of mudstone, siltstone and sandstone. Beneath this unit is the regionally extensive Pierre Shale, as well the marine and near shore sedimentary formations of the Colorado and Dakota Groups (Murphy et al., 2009).

3 Hydrogeology

3.1 General Description

The project area is underlain by several aquifers contained within the geologic units described in the previous subsection. The most prolific aquifers occur in the Oahe and Coleharbor deposits, where pumping rates can exceed 1,000 gpm. Deeper Tertiary and Cretaceous bedrock formations contain several aquifer intervals that exhibit variable production rates and water quality.

3.2 Surficial Aquifers

The North Dakota State Water Commission has identified several individual aquifers within the project area in the MRT. The Coleharbor meltwater deposits and the alluvial deposits of the Oahe Formation form the aquifers. The segments of these aquifers closest to the Missouri River were all included in the AEM survey, and three of the aquifers on the east side of the Missouri River were included in the ground-based geophysical investigation (Kume and Hansen, 1965; Bluemle, 1971). Each aquifer is briefly described in this section, however, it should be noted that the amount of hydrogeologic data available varies by individual aquifer in state reports.

The Painted Woods aquifer is located along the east bank of the Missouri River between Washburn and the McLean-Burleigh County line and is the aquifer analyzed beneath Line 1 in the ground-based geophysical survey described in this report. This aquifer spans an area of approximately nine square miles and averages around 70 ft in thickness. A thicker zone is apparent in the eastern half of the aquifer where a buried valley is present. In this area, the aquifer thickness approaches 125 ft. An approximately 30 ft thick silty clay layer creates confined conditions across much of this aquifer.

Transmissivity and storativity values, based on a 4-day aquifer test, were calculated at 26,200 feet squared per day (ft2/d) and 0.00045, respectively (Klausing, 1974). Upstream and to the west of Washburn are the Riverdale and Fort Mandan aquifers. The Riverdale aquifer occupies a four-square mile area on the east side of the Missouri River immediately downstream of Garrison Dam. Thickness of the Riverdale aquifer ranges from around 30 ft to over 90 ft (Klausing, 1974). The Fort Mandan aquifer covers a 16-square mile area on both sides of the Missouri River where the river flows west to east upstream of Washburn. Thickness of this aquifer ranges from approximately 30 to 60 ft. However, no aquifer test data is available for these two groundwater sources.

In Burleigh County, four surficial aquifers are present on the east side of the Missouri River between McLean County line and the city of Bismarck. About 3.5 miles south of the McLean County line, the Glenview aquifer underlies about 5 square miles of the MRT east of the Missouri River. No aquifer test data or thickness data is available, although it is expected that hydrologic characteristics of the aquifer is similar to other aquifers within the MRT (Randich and Hatchett, 1966). South of the Glenview aquifer is the Wagonsport aquifer, which was partially assessed by Line 2 and Line 4 in the ground-geophysics investigation. This aquifer is hosted by a sequence of sand and gravel that ranges in thickness from 20 to 50 ft and is not considered to be confined. Immediately north of Bismarck is the Burnt Creek aquifer.

Only a small portion of the aquifer falls within the coverage of the AEM survey and no ground-based geophysical measurements were taken in this area. The aquifer has variable thickness, ranging from 20 to over 100 ft. In addition to recharge from precipitation, Burnt Creek, which flows westward across the aquifer, also provides recharge as losing conditions typically persist in this surface drainage (Randich and Hatchett, 1966). Along the Missouri River beneath the city limits of Bismarck and southward is the Bismarck aquifer. Portions of this aquifer were included in the southern AEM flight area as well as Line 3 in the ground-based geophysical investigation. Covering 25 square miles, the aquifer ranges in thickness from 10 to over 100 ft, with an average of 50 ft. Aquifer tests conducted by the North Dakota State Water Commission indicate transmissivities in this aquifer range from 21,390 to nearly 47,000 ft2/d, with storativity ranging from 0.00012 to 0.00048 (Randich and Hatchett, 1966).

Each of the surficial aquifers described in this section show seasonal fluctuations in water levels in response to recharge from precipitation as well as changes…