NCD003162542_Badin Business Park_Corrective Action_20220222

Badin Business Park LLC c/o Alcoa Corporation 201 Isabella Street Suite 500 Pittsburgh, PA 15212-5858 USA Tel: [phone]

February 22, 2022
Robert C. McDaniel
Facility Management Branch Hazardous Waste Section North Carolina Department of Environmental Quality 217 West Jones Street
Raleigh, North Carolina 27603
Re: Geophysical Evaluation – Alcoa Badin Landfill Badin Business Park (f/k/a Alcoa - Badin Works) Badin, North Carolina
EPA ID: NCD 003 162 542
Dear Mr. McDaniel:
Please find enclosed the Geophysical Evaluation Down Gradient of the Alcoa Badin Landfill, 2021
Geophysical Evaluation, dated February 17, 2022. The report is the second in a series of planned
recurring geophysical surveys at the Alcoa/Badin Landfill intended to evaluate the long-term effects of the collection system as a function of time-series concentration dynamics.
This evaluation is being performed as a voluntary action beyond that required of the Investigative Work Plan for the Phase 4 and 5 Corrective Measures Study, Alcoa/Badin Landfill, and Former
Ball Field, dated April 2, 2018, and the associated Addendum to the Work Plan, dated April 15,
2019.
BBP appreciates the time and effort your office has spent on this project, and we look forward to continued progress. Should you have any questions or comments, please contact Jason Mibroda of Alcoa at [phone] at your convenience.

Sincerely,
Ronald M. Morosky
Director, Corporate Remediation and Technology
GEOPHYSICAL EVALUATION DOWN GRADIENT OF THE ALCOA BADIN
LANDFILL
2021 GEOPHYSICAL EVALUATION
PREPARED FOR
CIVIL & ENVIRONMENTAL CONSULTANTS, INC.
by
Geo Solutions Ltd.
GEO SOLUTIONS LIMITED, INC.
CONWAY, NORTH CAROLINA
February 17, 2022

TABLE OF CONTENTS
1.0 INTRODUCTION ............................................................................................................................ 1
1.1 OBJECTIVE ..................................................................................................................................... 1
2.0 GEOPHYSICAL TECHNIQUES ................................................................................................... 2
2.1 Multifrequency Electromagnetic Survey Theory ........................................................................... 2
2.2 Field Implementation ...................................................................................................................... 3
2.3 Method Verification and Data Quality ........................................................................................... 5
3.0 EM RESULTS................................................................................................................................... 6
3.1 October 2021 Results ..................................................................................................................... 6
3.2 Comparison to Historical Surveys ................................................................................................. 6
4.0 CONCLUSIONS ............................................................................................................................... 9
5.0 REFERENCES ............................................................................................................................... 10

LIST OF FIGURES
Figure 1. Site Map of Study Area Figure 2. 2021 EM Profile Location Map Figure 3. Map of the 2021 Electromagnetic (EM) Profile Locations
Figure 4. Map of the Results of the 2018 Baseline EM Evaluation
Figure 5. Comparison Results Map Figure 6. Map of the Constrained Areas for Comparison LIST OF APPENDICES Appendix A. Quality Assurance and Quality Control Results

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1.0 INTRODUCTION
Geo Solutions Limited, Inc. (Geo Solutions) is pleased to submit this report to Civil & Environmental Consultants, Inc. (CEC) documenting a geophysical evaluation performed at the Alcoa/Badin Landfill (ABL). The evaluation included the downgradient area between the ABL and Little Mountain Creek, and referred to as the Site. The Site is located on Wood Street in Badin,
North Carolina. Please refer to Figure 1 which serves as a location map of the Site and delineates
the study area. 1.1 OBJECTIVE
As presented in the April 2, 2018 Investigative Work Plan for the Phase 4 And 5 Corrective
Measures Study, Alcoa/Badin Landfill, And Former Ball Field as prepared by ENVIRONEERING, Inc., the North Carolina Department of Environmental Quality (NCDEQ) identified two objectives relating to the area downgradient of the landfill. The first objective was to map the areal extent of elevated constituent levels in the area downgradient of the landfill. The second objective was to
monitor the effects of a new trench collection system on the Site-wide flow system and the
constituent concentrations. To accomplish the objectives, a series of electromagnetic (EM) geophysical surveys was proposed to evaluate the electrical conductance in soil pore water. This methodology is supported as a means
to evaluate elevated constituent levels based on Benson’s correlation between inorganic water
chemistry data and electrical-based geophysical method data (Benson 1985). Furthermore, recurring EM surveys can be used to evaluate the long-term effects of the collection system as a function of time-series concentration dynamics (Benson 1988).
In the initial phase of this project, a series of EM geophysical surveys was performed at the Site to
evaluate the potential for seasonal variability in soil pore water conductivity. Quarterly baseline geophysical surveys were conducted for a period of one year; starting in the second quarter of 2018 and ending in the first quarter of 2019. The reference baseline surveys were intended for use as recurring assessment comparisons against succeeding geophysical evaluations of the Site. Based
on the findings of the quarterly baseline surveys, fall was selected as the preferable season to
perform follow up EM surveys and time series comparisons due to the contrast against the background EM response. Results are documented in the May 2019 Geophysical Evaluation Down Gradient of the Alcoa Badin Landfill to Evaluate Seasonal Variability in Electromagnetic Response (2019 Report), as prepared by Geo Solutions.

In October 2020, the first of a series of planned recurring geophysical surveys at the Alcoa/Badin Landfill was performed. The recurring surveys are intended to evaluate the long-term effects of the collection system as a function of time-series concentration dynamics. Results of the first follow up survey are documented in the December 11, 2020 Geophysical Evaluation Down Gradient of the
Alcoa Badin Landfill, 2020 Geophysical Evaluation as prepared by Geo Solutions. A subsequent
follow up geophysical survey for 2021 is the subject of this report.

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2.0 GEOPHYSICAL TECHNIQUES 2.1 Multifrequency Electromagnetic Survey Theory As presented in the literature reference above, dissolved constituents in soil pore water will increase its electrical conductivity with respect to background soil pore water conditions. The soil pore
water target, containing dissolved conductive materials, has a characteristic combination of
electrical conductivity, magnetic permeability properties, and geometrical shape and size. When the target is exposed to a low-frequency electromagnetic field, it produces a secondary magnetic field. By measuring the broadband spectrum of the secondary field, it is possible to obtain a distinct spectral signature that may uniquely identify the target. Thus, the response spectrum from
conductive material is a “fingerprint” of the composition of the target. This forms the general
principles of electromagnetic induction spectroscopy (EMIS) (Won 1998). The deployed EM method is a non-contact (uncoupled) geophysical method that utilizes a multiple frequency electromagnetic detector (Geophex Model GEM-2). The EM instrument collects
electromagnetic responses in the in-phase (metal detection or magnetic susceptibility mode) and
quadrature (apparent conductivity) mode. The GEM-2 operates in a frequency band between 30 Hz and 93 kHz where detection depth is inversely related to frequency. In other words, a low frequency signal travels farther into the earth and can “see” deep features while a high frequency signal can only travel short distances and therefore can only “see” shallow features. Therefore, if materials or
conductive groundwater at depth is concentrated in a particular zone, one frequency may “see” the
affected area more clearly than others. However, higher frequency bands tend to provide greater resolution with a higher signal to noise ratio. Below is a nomogram created by Geophex to display the estimated depth of detection as it relates to frequency and geology.
Multiple frequency electromagnetic evaluations are useful in characterizing targeted materials as
well as the distribution of elevated conductivities in soil pore water across a site.

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2.2 Field Implementation
On October 28, 2021, Geo Solutions performed the second follow up EM evaluation of the Site.
The approximate area evaluated was twelve (12) acres. The EM profile alignments were the same as collected during the baseline evaluations and the 2020 evaluation.
• During the baseline survey, Geo Solutions placed permanent stakes marking the EM profile
endpoints throughout the Site. The stakes were spaced sixty (60) feet apart and ran from the perimeter fence near the toe of the landfill to Little Mountain Creek for a total of twenty (20) profile lines. For navigation assistance, each stake was marked with a number and alternated in color (red and white) thereby providing consistency between the quarterly
evaluations. These stakes were still in place during the 2021 evaluation.

• The GEM-2 was operated in wireless configuration while performing the EM evaluation of the Site. The GEM-2 unit was either mounted on PVC tubular sled and towed with a Polaris Ranger all-terrain vehicle (ATV) or hand carried (photographs below). The advantage of
mounting the GEM-2 on a sled is related to efficiency of data collection and stability of the unit. When mounted on the sled, the GEM-2 is positioned approximately 0.75 meters from the ground surface. In this configuration, data was collected along the gravel road parallel to the collection trench at the toe of the landfill slope. The GEM-2 was hand carried in the remaining areas that included the slope of the landfill and the 20 transects in the area south
of the landfill.
Photograph showing typical deployment of GEM-2 EM Profiler mounted on sled.

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Photograph showing typical deployment of GEM-2 EM profiler in walking mode.
• Data was collected at the rate of thirty samples per second. The position of each sample
point was measured utilizing a Hemisphere Model A-325 GPS unit, which was augmented by the Wide Area Augmentation System (WAAS) and capable of sub-meter accuracy. The GPS unit allowed for EM data to be correlated to real-time location data. The GEM-2 and GPS communicated to a handheld data collector.
• Prior to beginning and before ending the EM survey, a quality assurance and quality control (QA/QC) profile was surveyed to test the response of the GEM-2 EM profiler. The QA/QC profile was 50-feet long with a steel plate in the center. The results of the QA/QC profile are shown in Appendix A at the rear of the report.

• Geo Solutions performed the EM evaluation as parallel profiles along the gravel road and the toe of the landfill, and along the staked profiles through the area south of the landfill (Figure 2). An effort was made to traverse the same transects as the baseline evaluation.
The sample spacing along each profile is a function of rate of travel of the sled or the pace
of walking. Here, the average sample spacing along each profile was less than 1 foot.
• The EM data were collected simultaneously at six varying frequencies (1,470 Hz, 4,110 Hz,
9,810 Hz, 32,190 Hz, 60,000 Hz, and 90,030 Hz). The 32,190 Hz frequency EM response
produced the best contrast to background conditions over the Site. This is likely related to the depth of conductive soil pore water. Based on the skin depth nomogram, the 32,190 Hz is most representative of the upper 4 to 6 feet corresponding to the targeted subsurface interval.

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• The EM data was transferred from the GEM-2 to a laptop computer using the WinGEM
Version 3 software provided by the manufacturer. During the transfer process, the
WinGEM software assigns Universal Transverse Mercator metric coordinates to each data collection station, and calculates the apparent conductivity for each frequency collected using the system software. These data were then transferred to a Microsoft Excel spreadsheet and reviewed for data anomalies such as poor GPS confidence levels that would
likely result in poor coordinate assignments. These data were used to compile a series of
maps illustrating various responses using a contour mapping program (Golden Software’s Surfer Mapping System Version 18). 2.3 Method Verification and Data Quality

Expected differentials in the EM response from the landfill to the area south of the landfill were confirmed during the recurring EM evaluation with the landfill having stronger EM response as compared to the area south of the landfill. This would indicate that the data quality is of high integrity as it is expected that the landfill would have more conductive soils and pore water than
the downgradient area. QA/QC profiles collected prior to beginning and after completion of the
survey indicate the GEM-2 was working properly during the recurring EM evaluation (Appendix A).
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3.0 EM RESULTS
As presented in Section 1.0, NCDEQ identified objectives relating to the areal extent of elevated
constituent levels in the area downgradient of the landfill and the effects of the trench collection system on the Site-wide flow system and constituent concentrations. The first objective was been successfully addressed via the series of baseline surveys. To accomplish the second objective, recurring EM surveys were proposed, the first of which was performed in October 2020. Results of the October 2020 survey were compared to the baseline survey established in October 2018. As
documented in the 2019 Report, a slight reduction in areal extent of elevated apparent conductivity values and a weaker EM response was observed between 2018 and 2020. To continue evaluating the long-term effects of the collection system as a function of time-series concentration dynamics, the results of the October 2021 survey were compared to the baseline survey established in October 2018 as well as the 2020 evaluation. The results of the comparisons are summarized in the
following.
3.1 October 2021 Results
Field data collection for the 2021 EM evaluation was performed on October 28, 2021. Site soil conditions were dry during the survey with a small isolated area of standing water on the west end of the survey area south of the landfill. EM data was collected from six varying frequencies, as noted previously, with the 32,190 Hz frequency EM response producing greatest contrast to background Site conditions. Please refer to Figure 3 for the results of the 32,190 Hz apparent
conductivity. The contrast between apparent conductivity values during the evaluation was excellent with a notable contrast between background Site conditions and areas of elevated apparent conductivity values. The orange and red hues indicate areas of elevated apparent conductivity values while the yellow and green hues indicate background Site conditions.
The demarcation between elevated apparent conductivity values and background Site conditions appears at approximately a value of 50 millisiemens per meter (mS/m). Apparent conductivity values increase to over 100 mS/m at the collection trench. Background conditions approaching 0 mS/m were observed along Little Mountain Creek indicating that soil pore water containing elevated apparent conductivity values was not intersecting Little Mountain Creek.
One additional area of slightly elevated apparent conductivities was observed on the west side of the survey area. This area was less wet as compared to the 2020 evaluation however the EM apparent conductivity values remain slightly elevated. Three areas of elevated apparent conductivity along the slope of the landfill were noted and are believed to be related to the former
seep collection areas. Several anomalous areas of elevated apparent conductivity of up to 1,000 mS/m were observed which were attributed to the existing collection system infrastructure at the Site including the leachate collection force main subsurface piping.
3.2 Comparison to Historical Surveys
Results of the October 2018 baseline evaluation are presented on Figure 4. The results of this baseline evaluation were used to assess the morphology of elevated apparent conductivity areas between the 2018 and the 2021 evaluation.
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As discussed above, the 50 mS/m contour was selected as the boundary indicator for elevated apparent conductivity conditions. Demonstrating the areal extent of elevated apparent conductivity,
an overlay of the 2018 baseline, 2020 evaluation, and the 2021 evaluation 50 mS/m
isoconcentration lines is presented as Figure 5. The total area which has apparent conductivity values of greater than 50 mS/m is smaller (2.04 acres) in the 2021 data than in the 2018 data (3.17 acres), representing a 35.7% reduction between the two events. Moreover, when considering the 2020 evaluation as well, a downward trend can be observed in the areal extent of the 32, 190 Hz
apparent conductivity EM values greater than 50 mS/m (See Chart below).
Comparison of the areal extent of the 32, 190 Hz EM values over 50 mS/m from 2018 to 2021.
To evaluate the intensity of the EM response over time, a time-series comparison between average apparent conductivity response values was performed for two evaluation areas. Evaluation areas were established for both downgradient of the perimeter fence and upgradient of the collection trench along the toe of the landfill slope. Figure 6 is a map displaying the locations of the evaluation area boundaries. The two boundaries were used to constrain the 32,190 Hz apparent conductivity
grid data. Using Surfer 18’s statistical analysis feature, the grid data from the 2018 baseline, 2020, and 2021 evaluations were exported from Surfer 18 and tabulated in Microsoft Excel.
The results of this comparison indicate the overall EM response is weaker in 2021 than in 2018 in both areas. The area downgradient of the perimeter fence had an average 32,190 Hz apparent
conductivity value during the 2021 evaluation of 27.17 mS/m while the 2018 evaluation average value was 36.0 mS/m, representing a 24.5% reduction between the 2021 and 2018 events. The average apparent conductivity values measured within the bounded area upgradient of the collection trench in 2020 and 2018 were 69.4 mS/m and 101.8 mS/m respectively, representing a 31.8% reduction between the two events. Moreover, when considering the 2020 evaluation as well, a
downward trend can be observed in the intensities of the downgradient and upgradient areas from
0
0.5
1
1.5
2
2.5
3
3.5
2018 2020 2021Acres
Year of EM Survey
Areal Extent of EM Values over 50 mS/m

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2018 to 2021. Shown on the chart below is the average values of the 32, 190 Hz apparent conductivity EM values from 2018 to 2021 in the wetland area downgradient of the collection
trench.
EM intensity of the wetland area downgradient of the collection trench.

0
5
10
15
20
25
30
35
40
2018 2020 202132,190 Hz Apparent Conductivity (mS/m)Year of EM Survey
EM Intensity of Wetland Area Downgradient of Collection
Trench
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4.0 CONCLUSIONS
The objective of the 2021 EM evaluation at the Site was to evaluate the long-term effects of the
collection system as a function of time-series concentration dynamics. The 2021 EM evaluation
was successful in mapping the areal extent of the elevated constituent levels as a function of apparent conductivity downgradient of the landfill. A comparison to the baseline survey indicates the areal distribution of apparent conductivity across the downgradient area is similar in shape to the 2018 baseline evaluation with a 35.7% reduction in overall size. A comparison of
2021 apparent conductivity response intensity indicates that the areas downgradient of the
perimeter fence and upgradient of the collection trench are weaker compared to the 2018 baseline evaluation. When considering all three survey events, a downward trend in areal extent and EM intensity was observed.

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5.0 REFERENCES
Benson, R.C., M.S. Turner, W.D. Vogelsong and P.P. Turner, 1985 Correlation between field geophysical measurements and laboratory water sample analysis, Proceedings of the Conference on Surface and Borehole Geophysical Methods in Ground Water Investigations, National Water Well Association, Worthington, OH, pp. 178–197, 1985.

Benson, R.C., M.S. Turner, P.P. Turner and W.D. Vogelsong, 1988 In situ, time-series measurements for long-term ground-water monitoring, in Ground Water Contamination: Field Methods, ASTM STP 963, Collins, A.G. and Johnson, A.I. Eds., American Society for Testing and Materials, Philadelphia, PA, 1988, pp. 58–72.

I.J. Won, D.A. Keiswetter, and E. Novikova, 1998, Electromagnetic induction spectroscopy,
Journal of Environmental and Engineering Geophysics, v. 3, Issue 1, pp. 27-40.

Appendix A. 2021 Quality Assurance and Quality Control EM Profiles.

25.00
30.00
35.00
40.00
45.00
50.00
0 10 20 30 40 50
32,190 Hz Apparent Conductivity (mS/m)Distance (ft)
QA/QC Profile 1
25.00
30.00
35.00
40.00
45.00
50.00
0 10 20 30 40 50
32,190 Hz Apparent Conductivity (mS/m)Distance (ft)
QA/QC Profile 2