SYNT00219_Report_rev_050219

Solutions
821 Livingston Court, Suite E
Marietta, Georgia 30067
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www.gel-solutions.com
Additional Geophysical Survey for the Detection of Possible Diabase Dikes
Duke Energy Cape Fear Plant
Moncure, North Carolina
Performed for:
SynTerra
May 2, 2019
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Additional Geophysical Survey for the Detection of Possible Diabase Dikes
Duke Energy Cape Fear Plant
Moncure, North Carolina
TABLE OF CONTENTS
Section Page
SignaturePage...................................................................................................................................ii
ExecutiveSummary.........................................................................................................................iii
1.0 Introduction........................................................................................................................... 1
1.1 Background...................................................................................................................1
2.0 Equipment and Methodology................................................................................................ 1
2.1 G-858G Cesium Vapor Magnetometer......................................................................... 2
2.2 Ground Conductivity and Magnetic Susceptibility Instrument (CMD-4)...................... 2
3.0 Field Procedures.............................................................................................................................. 3
4.0 Data Interpretation and Results............................................................................................ 3
5.0 Conclusions and Recommendations...................................................................................... 4
Figures
Figure 1: Magnetometer Data (Top Sensor)
Figure 2: Magnetometer Data (Bottom Sensor)
Figure 3: Gradiometer Data
Figure 4: CMD-4 Ground Conductivity Data
Figure 5: CMD-4 In -phase Data
Figure 6: Combined Magnetometer Data (2016 and 2019 Surveys), Top Sensor
Figure 7: Combined Magnetometer Data (2016 and 2019 Surveys), Top Sensor, Coal Pile Assessment Area
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Signature Page
This report, entitled "Additional Geophysical Survey for the Detection of Possible Diabase Dikes, Duke
Energy Cape Fear Plant, Moncure, North Carolina" has been prepared for SynTerra located in Greenville, South
Carolina. It has been prepared under the supervision of Mr. Jorgen Bergstrom at the request of and for the
exclusive use of SynTerra. This report has been prepared in accordance with accepted quality control practices
and has been reviewed by the undersigned.
GEL Solutions
A Member of the GEL Group, Inc.
Jorgen Bergstrom, P.Gp.
Principal, Seenior/Ge ysicist
Eric Armstrong
Geophysics Speci ist
May 2, 2019
Date
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Additional Geophysical Survey for the Detection of Possible Diabase Dikes
Duke Energy Cape Fear Plant
Moncure, North Carolina
EXECUTIVE SUMMARY
GEL Solutions performed a geophysical investigation at the Duke Energy Cape Fear Plant located in
Moncure, North Carolina. The fieldwork was conducted on April 4-5, 2019 at the location of the former coal
stockpile areas, and former steam electric plant area. The geophysical investigation was designed to identify
magnetic anomalies that are possibly indicative of the presence of diabase dikes at the approximately 15-acre
area (referred to as the Coal Stockpile Assessment Area). The main geophysical equipment used onsite
consisted of a Geometrics' G-858G Cesium Vapor Magnetometer and a GF Instruments CMD-4 electromagnetic
ground conductivity and magnetic susceptibility system. Trimble R6 and Trimble R10 Real Time Kinematic (RTK)
Global Positioning System (GPS) was used for positioning anomalies, geophysical sensors, and the location of
surface metal, monitoring wells, underground piping, and other features which could potentially impact the
readings from the geophysical instruments.
The magnetometer data collected during this field campaign was merged with magnetometer data
collected by GEL Solutions around the perimeter of five basins in 2016 (see report titled "Magnetometer Survey
for the Detection of Possible Diabase Dikes, Duke Energy Cape Fear Plant, Moncure, North Carolina", March 17,
2016). Based on the interpretation of the geophysical data collected, GEL Solutions identified one linear
magnetic anomaly consistent with the anticipated response of a diabase dike. The feature is striking
approximately 25° west of north. One unknown linear magnetic feature parallel to the possible diabase dike
was detected in the southeast corner of the Coal Stockpile Assessment Area. This feature has the characteristics
of a diabase dike, but could also be caused by cultural interference, such as underground utilities. No
continuation of the feature could be detected in the 2016 data south or north of the Coal Stockpile Assessment
Area. GEL Solutions recommends that these features be investigated by intrusive means. The presence of
surface and subsurface metallic objects reduced the effectiveness of the geophysical methods in the western
and southern parts of the Coal Stockpile Assessment Area for finding and delineating any possible diabase dikes.
Although geophysical methods provide a high level for the assurance for the location of subsurface
objects, the possibility exists that not all features were identified. Due caution should be used in excavation
where potential hazards exist. This investigation was not designed to be a complete investigation of
underground utilities and other subsurface hazards.
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Additional Geophysical Survey for the Detection of Possible Diabase Dikes
Duke Energy Cape Fear Plant
Moncure, North Carolina
1.0 INTRODUCTION
GEL Solutions performed a geophysical investigation at the Duke Energy Cape Fear Plant located in
Moncure, North Carolina. The fieldwork was conducted on April 4-5, 2019. The geophysical investigation was
designed to identify magnetometer anomalies that are possibly indicative of the presence of diabase dikes at an
approximately 15-acre area at the location of former coal stockpile areas, and the former steam electric plant
area (referred to as the Coal Stockpile Assessment Area). The geophysical equipment used onsite consisted of a
Geometrics' G-858G Cesium Vapor Gradiometry Magnetometer system, and a GF Instruments CMD-4
electromagnetic ground conductivity and magnetic susceptibility system. Trimble R6 and Trimble R10 Real Time
Kinematic (RTK) Global Positioning System (GPS) was used for positioning anomalies, geophysical sensors, and
the location of surface metal, monitoring wells, underground piping, and other features which could potentially
impact the readings from the geophysical instruments.
1.1 Background
In a previous magnetometer survey conducted by GEL Solutions in 2016 around the perimeter of five
basins, a linear magnetic feature was detected in the northwest part of the site (see report titled
"Magnetometer Survey for the Detection of Possible Diabase Dikes, Duke Energy Cape Fear Plant, Moncure,
North Carolina", March 17, 2016). Since the plant was being demolished at the time of the 2016 survey, site
access was limited around the plant. Since the demolishing is now completed, SynTerra wished to have
additional areas scanned in more detail in order to further delineate this anomaly, and search for additional
possible diabase dikes at the location of the former plant and former coal stockpile areas. To support SynTerra
with these investigations, GEL Solutions conducted a magnetometer investigation using a roving Geometrics' G-
858G gradiometer instrument. Due to the historic use of the property, GEL Solutions suspected that cultural
interference in the form of metallic debris, buried concrete, and underground piping may still be present at the
site. GEL Solutions therefore conducted an electromagnetic survey of the site using a GF Instruments CMD-4
electromagnetic ground conductivity and magnetic susceptibility system, and a radio -frequency pipe and cable
locator to assess the amount and location of these types of cultural interference.
2.0 EQUIPMENT AND METHODOLOGY
The following is a brief introduction to the geophysical equipment used at the site.
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2.1 G-858G Cesium Vapor Magnetometer
The G-858G consists of two cesium vapor magnetometers. The sensors, which are separated by a vertical
distance of approximately four feet, measure the intensity of the earth's magnetic field at two elevations. The
principle of operation is that atomic electrons are excited (transferred to a higher energy level). The magnetic
field will cause the electrons to fall back in a spiraling fashion. The intensity of the magnetic field can be
measured by determining the frequency at which the electrons spiral back. Only ferrous objects will cause
fluctuations in the earth magnetic field and can therefore be detected with the G-858G. The sensor readings
and the vertical magnetic gradient are recorded at the measurement location. The vertical magnetic gradient is
calculated as the difference in the sensor readings divided by the separation distance. The data is stored and
displayed on a digital data logger. A GPS port on the logger allows simultaneous collection of G-858G and GPS
data. For some applications, after completion of the field data acquisition, the data can be transferred to a PC
for further processing and analysis using Geosoft Oasis Montaj or Surfer software. Magnetometer surveys can
be used to detect diabase dikes due to the higher magnetic susceptibility (a materials ability to become
magnetized in the presence of a magnetic field) of diabase compared to the host rock.
2.2 Ground Conductivity and Magnetic Susceptibility Instrument (CMD-4)
The CMD-4 instrument measures variations in electrical conductivity and magnetic susceptibility of
subsurface materials. The conductivity is determined by inducing a primary electromagnetic field and measuring
the amplitude and phase shift of an induced secondary magnetic field. The secondary magnetic field is created
by subsurface conductive materials behaving as an inductor as the primary field is passed through them.
Ground conductivity systems such as the CMD-4 are commonly used to delineate lateral extent of landfills.
There are two components of the induced electromagnetic field measured by the CMD-4 system. The first is the
quadrature-phase (out -of -phase) component that measures the bulk conductivity of soil and groundwater. The
conductivity readings increase or become negative when the sensors are close to metallic objects. The second is
the in -phase component that measures the magnetic susceptibility and is therefore more sensitive to isolated
metallic objects such as pipes, drums, underground storage tanks, and other metallic debris. Both positive and
negative readings indicate subsurface metal. By observing the response of the in -phase and quadrature-phase
components, it is possible to differentiate whether a change in bulk conductivity is due to the presence of buried
metallic objects or due to changes in subsurface soil conditions or pore fluid conductivity.
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The presence of metal buildings, fences, and other metallic surface objects cause interference and makes
data interpretation for subsurface features near these objects difficult. The CMD-4 has an effective depth of
exploration of up to approximately 20 feet below ground surface. However, the ability to detect small features
decreases with depth.
3.0 FIELD PROCEDURES
G-858G and CMD-4 data was collected across the Coal Stockpile Assessment Area along an orthogonal
set of transects spaced approximately 50 feet apart. The positioning of the data was derived using RTK/GPS
data. In order to check for diurnal variations in the earth magnetic field, GEL Solutions measured the earth
magnetic field every hour at a fixed base station location. In addition to these surveys, GEL Solutions also
conducted a limited radio frequency electromagnetic survey designed for detecting potential metallic
subsurface utilities. The detected utilities are shown on the attached figures.
RTK/GPS was used to measure the position of surface metal, monitoring wells, underground utilities, and
other sources of cultural noise in the data. Note that surface features were recorded for the sole purpose of
facilitating the geophysical investigation and should not be considered geodetically surveyed.
4.0 DATA INTERPRETATION AND RESULTS
Earth's magnetic field was found to only vary slightly over the period of the survey (maximum change of
approximately 20nT). Therefore, no diurnal corrections were made to the G-858G data. Figure 1 shows the top
sensor data of the G-858G system (mounted six feet above the ground surface). Bottom sensor (mounted two
feet above the ground surface) results are shown in Figure 2. The results of the collected gradient
measurements are shown in Figure 3. CMD-4 conductivity data is shown on Figure 4, and the in -phase data is
shown on Figure 5.
One linear magnetic anomaly consistent with the anticipated response of a diabase dike was detected in
the eastern parts of the Coal Stockpile Assessment Area. The potential diabase dike is striking approximately 25'
west of north (See attached Figures). The anomaly is greater in magnitude on the northern part of the Coal
Stockpile Assessment Area, which may indicate that the potential diabase dike is deeper or narrower at the
southern part of the Coal Stockpile Assessment Area. The location of the potential diabase dike correlates well
with the anomaly detected in this area in 2016. One unknown linear magnetic feature parallel to the possible
diabase dike was detected in the southeast corner of the Coal Stockpile Assessment Area (see Figures 1-3). This
feature has the characteristics of a diabase dike, but could also be caused by cultural interference, such as
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underground utilities. Based on the 2016 data, no continuation of the feature could be detected south or north
of the Coal Stockpile Assessment Area. At the western and southern parts of the Coal Stockpile Assessment
Area there appear to be an abundance of surface and subsurface metallic objects. Due to the high
concentration of metallic objects, the datasets could not be interpreted for geological features in this area
(marked with a solid white line in Figures 1-5). The top magnetometer sensor generated the best data for
detecting the diabase dike, possibly because this sensor is least affected by smaller metallic objects.
GEL Solutions combined the 2016 and 2019 surveys by adjusting the 2019 top sensor magnetometer data
to the 2016 level. The combined data is shown on Figures 6 and 7.
5.0 CONCLUSIONS AND RECOMMENDATIONS
Based on the geophysical investigation conducted at the site, GEL Solutions identified a linear magnetic
feature which is believed to be a diabase dike. The feature is striking approximately 25° west of north (see
attached Figures). One unknown linear magnetic feature parallel to the possible diabase dike was detected in
the southeast corner of the Coal Stockpile Assessment Area (see Figures 1-3). This feature has the
characteristics of a diabase dike, but could also be caused by cultural interference, such as underground utilities.
No continuation of the feature could be detected in the 2016 data south or north of the Coal Stockpile
Assessment Area. Intrusive investigations may be warranted in these areas to confirm the findings of the
geophysical investigation. The presence of surface and subsurface metallic objects reduced the effectiveness of
the geophysical methods in the western and southern parts of the site for finding and delineating any possible
diabase dikes.
Although geophysical methods provide a high level for the assurance for the location of subsurface
objects, the possibility exists that not all features were identified. Due caution should be used in excavation
where potential hazards exist. This investigation was not designed to be a complete survey of underground
utilities and other subsurface hazards.
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