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_rCaRO <br />FUGRO CONSULTANTS, INC. <br />Data Processing <br />Acquired data were uploaded to AGI Earth Imager© software as an initial QC measure at the end of each field <br />day, to ensure data quality and coverage. Final models for interpretation were generated through RES2DINV <br />ERT processing software from GeoTomo Software. GeoTomo performs electrical resistivity tomography using a <br />least squares approach. Data are viewed and edited for outliers prior to the tomographic inversion to reduce <br />model error and to prevent spurious artifacts. Data positioning (X,Y) were based on Real Time Kinematic (RTK) <br />global positioning system (GPS) coordinates for the center and both ends of each ERT line. These locations <br />were adjusted to best fit the Google Earth Satellite imagery, and then the position of each electrode was <br />interpolated between endpoints. The elevations for the electrode positions were then extracted from DEMs in <br />ArcGIS and used to establish the ground surface elevations for the 2-D model. <br />Results <br />Figure 5 shows the geo-electric section of each of the ERT lines with the start of each line (south end) shifted <br />relative to an East-West baseline to facilitate correlation between the adjacent lines. All the geo-electric sections <br />use a common color contoured resistivity scale, which is shown at the bottom of the figure. Low resistivity <br />values are shown in cool colors (blues) and high resistivity values are shown in hot colors (reds). The objective <br />of this survey was to map electrical anomalies in the area between the depressions in the drainage ditch and <br />possible vertical drainage in the area around the suspected airshaft which may indicate the movement of near <br />surface groundwater. To obtain higher resolution of these features the spacing between electrodes was <br />decreased from the 3 meters (used in the previous survey) to 1.5 meters. This decreased electrode separation <br />resulted in a decrease in the length of the area mapped along each line and in the effective depth of exploration <br />in this survey. <br />The hot (>90 degrees F) and dry weather during and preceding data collection resulted in significantly higher <br />contact resistances for the electrodes relative to the first survey which was done in early April. This required <br />additional wetting of the electrodes during data collection to minimize signal noise. <br />Generally, the results from the April survey in areas of overlap are consistent with the results from the current <br />survey. The south portion of each line shows higher resistivity values and a more consistent layering, while the <br />northern halves show a broken near surface resistive surface layer underlain by more conductive units (greens <br />and blues). The thick more resistive unit on the south half of each line likely corresponds to the coarse poorly <br />graded alluvium. The combination of broken -up near -surface high resistivity and a lower resistivity unit on the <br />north end of each line, suggests the presence of a finer grained materials with greater clay content. Increased <br />water content within the subsurface may also cause a decrease in the bulk resistivity of the various layers. <br />Project/Proposal No. 04.79160011 August 23, 2016 <br />Page 5 of 7 <br />TR -69 A14-15-8 09/16 <br />