NCD003162542_Badin Business Park_Corrective Action_20240105

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

January 5, 2023

Robert C. McDaniel
Facility Management Branch
Hazardous Waste Section
North Carolina Department of Environmental Quality
217 West Jones Street
Raleigh, North Carolina 27603

Re: 2023 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, 2023
Geophysical Evaluation, dated January 2, 2024. The report is the fourth 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.
Should you have any questions or comments, please contact Jason Mibroda of Alcoa at (412) 315-
2783 at your convenience.

Sincerely,

Robyn L. Gross
Director, Asset Management Americas
Badin Business Park LLC

GEOPHYSICAL EVALUATION DOWN GRADIENT OF THE ALCOA BADIN
LANDFILL
2023 GEOPHYSICAL EVALUATION

PREPARED FOR CIVIL & ENVIRONMENTAL CONSULTANTS, INC.

by

GEO SOLUTIONS LIMITED, INC.
CONWAY, NORTH CAROLINA
January 02, 2024
Geo Solutions Ltd.

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 2023 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. 2023 EM Profile Location Map Figure 3. Map of the 2023 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 is 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 2020 through 2022 recurring annual surveys are documented in reports prepared by Geo Solutions. The 2023
recurring annual geophysical survey 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 23, 2023, Geo Solutions performed the fourth recurring 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 subsequent recurring annual evaluations. Weather conditions were dry at the time of the evaluation. Site conditions were also dry with little to no surface water except for in the channel of Little Mountain Creek. According to North Carolina
Climate Office Weather Station KVUJ, located at the Stanly County airport approximately 1.5 miles
from the landfill, the weather station only received 1.35 inches of rain in the month of September and only 0.36 inches in October at the time of the survey.
• 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. Several of these stakes were replaced during the 2023 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 which included the slope of the landfill and the 20 transects in the area
south of the landfill.

4

Photograph showing typical deployment of GEM-2 EM Profiler mounted on sled.
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

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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.

• 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 24).
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 has 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. To
continue evaluating the long-term effects of the collection system as a function of time-series
concentration dynamics, the results of the October 2023 survey were compared to the baseline survey established in October 2018 as well as subsequent recurring annual surveys. The results of the comparisons are summarized in the following. 3.1 October 2023 Results Field data collection for the 2023 EM evaluation was performed on October 23, 2023. Site soil conditions were dry during the survey. 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. An isolated area of slightly elevated apparent conductivities was observed on the west side of the survey area. Several 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.
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 2023 evaluation. 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, 2021, 2022, and 2023 evaluation 50 mS/m isoconcentration lines are presented as Figure 5. The total area which has apparent conductivity values of greater than 50 mS/m remained similar between 2022 and 2023 (1.49 acres) indicating a sustained reduction in aerial extent (See Chart below).

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Comparison of the areal extent of the 32,190 Hz EM values over 50 mS/m from 2018 to 2023. 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 24’s statistical analysis feature, the grid data from the 2018 baseline, 2020,
2021, and 2022 evaluations were exported from Surfer 24 and tabulated in Microsoft Excel.
The results of this comparison indicate the overall EM response is weaker in 2023 than in 2018 in both areas indicating a sustained overall reduction. The area downgradient of the perimeter fence had an average 32,190 Hz apparent conductivity value during the 2023 evaluation of 19.3 mS/m
while the 2018 evaluation average value was 36.0 mS/m, representing a 46.3% reduction between
the 2023 and 2018 events. The average apparent conductivity values measured within the bounded area upgradient of the collection trench in 2023 and 2018 were 74.3.76 mS/m and 101.8 mS/m respectively, representing a 27.0% reduction between the two events. The 2023 average apparent conductivity within the downgradient and upgradient areas is slightly higher than the 2022 survey,
however given the variability in regional weather conditions, temporal increases between recurring
survey events are not unexpected.
0
0.5
1
1.5
2
2.5
3
3.5
2018 2020 2021 2022 2023Acres
Year of EM Survey
Aerial Extent of EM Values over 50 mS/m

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EM intensity of the wetland area downgradient of the collection trench.

0
10
20
30
40
2018 2020 2021 2022 202332,190 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 2023 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 2023 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 47.0% reduction in overall size. A comparison of 2023 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.

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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.

-5.00
5.00
15.00
25.00
35.00
45.00
0 5 10 15 20 25 30 35 40 45 5032,190 Hz Apparent Conductivity (mS/m)Distance (ft)
QA/QC Profile 1
-5.00E+00
5.00E+00
1.50E+01
2.50E+01
3.50E+01
4.50E+01
0 5 10 15 20 25 30 35 40 45 5032,190 Hz Apparent Conductivity (mS/m)Distance (ft)
QA/QC Profile 2