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Home My WebLink AboutNC0003433_GEL Magnetometer Survey Report_20160915Engineering of NC INC an affiliate of The GEL Group IN'. 6541 Meridien Dr., Suite 101 Raleigh, NC 27616 P 919.544.1100 F 919.237.9177 Magnetometer Survey for the Detection of Possible Diabase Dikes Duke Energy Cape Fear Plant Moncure, North Carolina Performed for: SynTerra Corporation March 17, 2016 1 GEL Engineering of NC INC 6541 Meridien Dr., Suite101 Raleigh, NC 27616 P 919.544.1100 F 919.237.9177 www.gelgeophysics.com Magnetometer Survey for the Detection of Possible Buried 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-858 Cesium Vapor Magnetometer........................................................ 1 2.2 G-857 Proton Precession Magnetometer.......................................................2 3.0 Field Procedures.......................................................................................................... 3 4.0 Data Interpretation and Results.................................................................................. 3 5.0 Conclusions and Recommendations........................................................................... 4 Figures Figure 1 G-858 Magnetometer Survey Locations Figure 2 G-858 Magnetometer Survey Results for the Top Sensor Measurement Figure 3 G-858 Magnetometer Survey Results for the Bottom Sensor Measurement Figure 4 G-858 Gradient Measurement GEL Engineering of NC INC 6541 Meridien Dr., Suite101 Raleigh, NC 27616 P 919.544.1100 F 919.237.9177 www.gelgeophysics.com Signature Page This report, entitled "Magnetometer Survey for the Detection of Possible Diabase Dikes, Duke Energy Cape Fear Plant, Moncure, North Carolina" has been prepared for SynTerra Corporation located in Greenville, South Carolina. It has been prepared under the supervision of Mr. Kelly Plummer at the request of and the exclusive use of SynTerra Corporation. This report has been prepared in accordance with accepted quality control practices and has been reviewed by the undersigned. GEL Engineering of NC, Inc A Member of the GEL Group, Inc. Kelfry-R. Plummer Geophysicist Jorgen Bergstrom Senior Geophysicist March 17, 2016 Date GEL Engineering of NC INC 6541 Meridien Dr., Suite101 Raleigh, NC 27616 P 919.544.1100 F 919.237.9177 www.gelgeophysics.com Magnetometer Survey for the Detection of Possible Buried Dikes Duke Energy Cape Fear Plant Moncure, North Carolina EXECUTIVE SUMMARY GEL Engineering of NC, Inc. (GEL Engineering) performed a geophysical investigation from February 3 to February 11, 2016, at the Duke Energy Cape Fear Plant located at the end of CP and L Road in Moncure, North Carolina. This investigation was performed for SynTerra Corporation to locate any possible diabase dikes in the vicinity of five ash basins located at the site. The geophysical equipment used onsite consisted of a Geometrics' G-858 Cesium Vapor Magnetometer and a G-857 Proton Precession Magnetometer. A Trimble Geo 7x Global Positioning System (GPS) was used for positioning anomalies, geophysical sensors, and the location of surface metal, fences, concrete culverts, metallic posts, and other surface features which could potentially impact the readings from the geophysical instruments. The geophysical investigation was designed to identify magnetometer anomalies that are possibly indicative of the presence of diabase dikes around the existing ash basins. Based on the interpretation of the geophysical data collected, GEL Engineering identified three areas within the survey limits exhibiting magnetic anomalies indicative of possible diabase dikes. The areas are located in the north and central portions of the site and show a relatively high magnetic response. GEL Engineering recommends that these area be investigated by intrusive means to determine the source of the geophysical anomalies. Various obstructions throughout the site limited the ability to detect target features during the magnetometer survey due to signal interference and access issues. These obstacles included wetlands, steep slopes, structures, utilities, and other surface obstructions. 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 locate underground utilities and other subsurface hazards. GEL Engineering of NC INC 6541 Meridien Dr., Suite101 Raleigh, NC 27616 P 919.544.1100 F 919.237.9177 www.gelgeophysics.com Magnetometer Survey for the Detection of Possible Buried Dikes Duke Energy Cape Fear Plant Moncure, North Carolina 1.0 INTRODUCTION GEL Engineering performed a geophysical investigation at the Duke Energy Cape Fear Plant located at the end of CP and L Road in Moncure, North Carolina. The fieldwork was conducted from February 3 to February 11, 2016. This investigation was performed for SynTerra Corporation to locate any possible diabase dikes in the vicinity of five ash basins located at the site. The geophysical equipment used onsite consisted of a Geometrics' G-858 Cesium Vapor Magnetometer and a G-857 Proton Precession Magnetometer. A Trimble Geo 7x Global Positioning System (GPS) was used for positioning anomalies, geophysical sensors, and the location of surface metal, fences, concrete culverts, metallic posts, and other surface features which could potentially impact the readings from the geophysical instruments. The geophysical investigation was designed to identify magnetometer anomalies that are possibly indicative of the presence of diabase dikes around the existing ash basins. 1.1 Background SynTerra is currently involved in characterizing the areas around the known existing ash basins at the Duke Cape Fear Plant located in Moncure, North Carolina. In order to support SynTerra with these investigations, GEL Engineering conducted a geophysical investigation from February 3 to February 11, 2016, using a roving Geometrics' G-858 magnetometer instrument and a G-857 base station unit. The investigation was designed to detect the presence of any possible diabase dikes below the ground surface. 2.0 EQUIPMENT AND METHODOLOGY The following is a brief introduction to the geophysical equipment used at the site. 2.1 G-858 Cesium Vapor Magnetometer The G-858 consists of two cesium vapor magnetometers. The sensors, which are separated by a vertical distance of approximately three feet, measure the intensity of the GEL Engineering of NC INC 6541 Meridien Dr., Suite101 Raleigh, NC 27616 P 919.544.1100 F 919.237.9177 www.gelgeophysics.com Magnetometer Survey for the Detection of Possible Diabase Dikes Duke Energy Cape Fear Plant, Moncure, North Carolina (SYNT00116) March 17, 2016 Page 2 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-858. 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-858 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. 2.2 G-857 Proton Precession Maenetometer (Base Station The G-857 Proton Precession Magnetometer measures the scalar intensity of the local magnetic field. The instrument uses an induction coil to generate a magnetic field around a hydrogen -rich fluid. These fluids include kerosene, lighter fluid, mineral spirits, etc. This induction causes the hydrogen protons to align with the created magnetic field. When the produced magnetic field is disturbed, the protons then will align themselves with the Earth's magnetic field. This causes it to temporarily precess around the Earth's magnetic field at a specific frequency. This frequency is then related to the ambient magnetic field strength. The precession then creates a small magnetic field that produces alternating voltage in the induction coil. The G-857 is commonly used as a base station in many magnetometer surveys. It is placed in area away from surface metal or areas that could have interaction with metallic objects such as cars. The instrument measures the variation of the Earth's magnetic field during the magnetometer survey. At the completion of the survey, the G-857 data is removed from the data logger and used to correct the magnetometer data collected at site by the rover magnetometer system. This correction is typically performed using MagMap software. GEL Engineering of NC INC 6541 Meridien Dr., Suitel01 Raleigh, NC 27616 P 919.544.1100 F 919.237.9177 www.gelgeophysics.com Magnetometer Survey for the Detection of Possible Diabase Dikes March 17, 2016 Duke Energy Cape Fear Plant, Moncure, North Carolina (SYNT00116) Page 3 3.0 FIELD PROCEDURES The G-857 proton precession magnetometer was placed in a location on the site relatively close to where G-858 data was being collected. The G-857 collected continuous measurements while the survey was being performed and at the end of the day of the investigation the data was removed from the system. G-858 data was collected along selected paths along the accessible areas of the landfill perimeters. Transect spacings were between approximately 20 to 50 feet and were routinely altered due to obstructions such as trees, debris piles, wetlands, utilities, etc. Some areas around the parameter of the landfills could not be properly investigated due to power plant structures, wetlands, or other obstructions. The positioning of the data was derived using GPS data. Transect paths are shown in Figure 1. GPS was also used to measure the position of debris piles, fences, utility surface features, metal post, easements, and other features in order to determine if these objects were causing anomalies in the geophysical data and for positioning control. 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 The G-857 base station data showed a relatively small change in the Earth's magnetic over the period of the survey with a maximum change of approximately 20 nT during a survey day. Therefore, no diurnal corrections were made to the G-858 data. The G-858 data transect locations and limits of the investigation are shown in Figure 1. Figure 2 shows the top sensor data of the G-858 system and bottom sensor results are shown in Figure 3. The results of the collected gradient measurements are shown in Figure 4. Four anomalous areas with responses indicative of possible diabase dikes were identified from the collected data and are shown in Figure 2 and Figure 3. Three of these four areas have a response and a liner layout for the location of a possible diabase dike. Two of these locations do have some possible interference from nearby utility structures, but these GEL Engineering of NC INC 6541 Meridien Dr., Suitel01 Raleigh, NC 27616 P 919.544.1100 F 919.237.9177 www.gelgeophysics.com Magnetometer Survey for the Detection of Possible Diabase Dikes Duke Energy Cape Fear Plant, Moncure, North Carolina (SYNT00116) March 17, 2016 Page 4 anomalies have a similar magnetic response and appear to have a linear layout in a northwest orientation. There are several magnetic responses in data, but most of these can be linked to surface metallic objects or utilities in the area. The quality of the magnetometer data was negatively impacted by the large amount of metallic objects on the surface of the survey site. 5.0 CONCLUSIONS AND RECOMMENDATIONS Based on the geophysical investigation conducted at the site, GEL Engineering identified four areas with anomalies that we believe may be indicative of possible diabase dikes. Three of these four areas have a response and a linear layout for the location of a possible diabase dike. The identified areas are shown in Figures 2 and 3. The northwest orientation of the identified possible dike does correlate with the trend of other diabase dikes mapped in the area. The geologic maps provided by the Client show that diabase dikes in the area also have a northwest orientation. Intrusive investigations may be warranted in these areas to confirm the findings of the geophysical investigation. The presence of metallic objects on the ground surface and obstructions (fences, wetlands, debris piles, etc.) reduced the effectiveness of the geophysical methods in certain areas 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 locate underground utilities and other subsurface hazards. GEL Engineering of NC INC 6541 Meridien Dr., Suitel01 Raleigh, NC 27616 P 919.544.1100 F 919.237.9177 www.gelgeophysics.com