2024_Napaskiak_Remediation_Report_0001.pdf

FINAL

2024 Site Characterization Report

For the Napaskiak Former BIA School Day Tanks

Napaskiak, Alaska

ADEC File. No. 2433.38.004 ADEC Hazard ID 25241

Prepared for:

BUREAU OF INDIAN AFFAIRS

ALASKA REGIONAL OFFICE

3601 C STREET

ANCHORAGE, AK 99503

Prepared by:

TANANA COMMERCIAL COMPANY LLC

PO BOX 77069

TANANA, ALASKA 99777

April 2025

Site Characterization Report – FINAL Napaskiak Former BIA School Day Tanks; ADEC File No. 2433.38.004 April 2025 i

FINAL

Site Characterization Report

ADEC File No. 2433.38.004

Prepared by:

Tanana Commercial Company LLC PO Box 77069 Tanana, Alaska 99777

Written by:

Shayla Marshall, QEP Project Manager

April 2025 ii

TABLE OF CONTENTS

1.0 SITE DESCRIPTION AND BACKGROUND

1.1 Project Purpose and Objectives

1.2 Site Location

1.3 Background

2.0 INTERVIEWS AND RECORDS REVIEW

2.1 Interviews

2.2 Ownership Records Review

3.0 CONTAMINANTS OF CONCERN AND APPLICABLE

REGULATIONS

4.0 SAMPLING METHODOLOGY

4.1 Soil Sampling Methods

4.2 Groundwater Development and Sampling Methods

5.0 FIELD ACTIVITIES

5.1 Work Plan Variances

5.2 Site Characterization Activities

5.2.1 Test Pits

5.2.2 Monitoring Well Installation

5.2.3 Water Level Measurements and Flow Direction

5.3 Fall 2024 Monitoring Well Sampling

5.4 Decontamination Procedures

6.0 SAMPLING RESULTS

6.1 Subsurface Conditions

6.2 Test Pit Soil Results

6.3 July 2024 Groundwater Monitoring Results

6.4 October 2024 Groundwater Monitoring Results

7.0 QUALITY CONTROL REVIEW

7.1 SGS Report 1243966 Soil Samples

7.2 SGS Report 1243965 July Groundwater Samples

7.3 SGS Report 1245835 October Groundwater Samples

8.0 DISCUSSION

8.1 Soil Sampling Discussion

8.2 Groundwater Monitoring Discussion

8.3 Conceptual Site Model Discussion

9.0 INVESTIGATIVE DERIVED WASTE MANAGEMENT

10.0 CONCLUSIONS AND RECOMMENDATIONS

11.0 REFERENCES

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TABLES

Table 1 – GPS Coordinates of Sample Locations Table 2 – July 2024 Water Level Measurements Table 3 – October 2024 Water Level Measurements Table 4 – Detected Soil Analytical Results Table 5 – Detected July 2024 Water Analytical Results Table 6 – Detected October 2024 Water Analytical Results

FIGURES

Figure 1 – Vicinity Map Figure 2 – Project Area Figure 3 – Historical Sample Locations Figure 4 – 2024 Soil Sample Locations Figure 5 – July 2024 Monitoring Well Samples Figure 6 – October 2024 Monitoring Well Samples

APPENDICES

Appendix A – Figures Appendix B – Limited Liability Report Ownership Documents Appendix C – Field Notes Appendix D – Resume of QEPs Appendix E – Photo Pages Appendix F – SGS Laboratory Reports and Laboratory Data Review Checklists Appendix G – Human Health Conceptual Site Model Graphic Form and Human Health

Conceptual Site Model Scoping Form and Standardized Graphic Appendix H – DEC Review Comment Table

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ACRONYMS AND ABBREVIATIONS

AAC Alaska Administrative Code ADEC Alaska Department of Environmental Conservation AK Alaska AST Aboveground Storage Tank bgs Below Ground Surface BIA Bureau of Indian Affairs BOD Biochemical Oxygen Demand COD Chemical Oxygen Demand COPC Compounds of Potential Concern DRO Diesel Range Organics GAC Granulated Activated Carbon GPS Global Positioning System IDW Investigation Derived Waste LKSD Lower Kuskokwim School District LOQ Limits of Quantitation mg/kg Milligrams Per Kilogram mg/L Milligrams per Liter mL Milliliter MTG Migration to Groundwater PAH Polyaromatic hydrocarbon PID Photoionization Detector PPE Personal Protective Equipment QC Quality Control QEP Qualified Environmental Professional RPD Relative Percent Difference SGS SGS North America TCC Tanana Commercial Company LLC VOC Volatile Organic Compound

April 2025 1

FINAL

Site Characterization Report

ADEC File No. 2433.38.004

This report outlines the 2024 site characterization activities at the Napaskiak Former Bureau of Indian Affairs (BIA) School Day Tanks in Napaskiak, Alaska. The site is identified as Alaska Department of Environmental Conservation (ADEC) Contaminated Sites File No. 2433.38.004, Hazard ID 25241.

Work is in accordance with the February 16, 2024 Contract No. 140A0524P0003 between the BIA and Tanana Commercial Company LLC (TCC).

1.0 SITE DESCRIPTION AND BACKGROUND

The subject property is an active ADEC Contaminated Site. The following outlines the purpose of the field activities, site location, and previous field activities.

1.1 Project Purpose and Objectives

The purpose of the project is to progress toward Cleanup Complete with Institutional Controls for the site. The project objectives include the following:

• Conduct a site characterization to delineate the lateral and vertical extent of contamination;

• Gather current site condition information to evaluate potential remedial options for the site;

and

• Install and conduct groundwater monitoring of five wells to determine groundwater conditions.

1.2 Site Location

The village of Napaskiak is located on the east bank of the Kuskokwim River, approximately 7 miles southeast of Bethel, Alaska. The site is located in the southwest ¼ of Section 9, Township 7 North, Range 71 West, Seward Meridian, Alaska (Bethel C-8 USGS Quadrangle). The Vicinity Map is included as Figure 1 (Appendix A). The location of the site within Napaskiak is shown on Figure 2.

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1.3 Background

The following documents were reviewed for history on the environmental activities previously conducted at the site. The sample locations referenced below are shown on Figure 3 in Appendix A.

Oasis Environmental. Draft Village of Napaskiak Site Reconnaissance Project Report. 19 October 2001.

A site investigation was performed at five current and former bulk fuel storage tank farms and pipelines; the former day tanks for the BIA school (Site 5) were included in this investigation. The other sites included the John Williams School Tank Farm, Napaskiak Utility Tank Farm, Napaskiak, Inc. Store Tank Farm, and Napaskiak. Inc. Store Tank Farm (Former Location) were also evaluated but are not included in the following summary.

The former school day tanks were located near the utility building for the BIA school. The tanks were no longer present but a fuel tank cradle comprising of treated wood remains remained at the time of the assessment. According to the Lower Kuskokwim School District personnel, a diesel fuel release was discovered in October 1993 and was associated with leaking fuel pipelines at the BIA school building complex and utility building. The piping and fuel tanks associated with the spill had been removed.

A stained area near the utility building was sampled. Elevated headspace readings were encountered at 1 and 3 feet below ground surface (bgs); a soil sample was collected from 3 feet bgs. A diesel range organic (DRO) concentration of 38,900 milligrams per kilogram (mg/kg) was reported in the sample and exceeded the ADEC cleanup level. Based on visual observation of stained soil, the approximate area of impact is 115 square feet and extends to 3 feet bgs. Further assessment was recommended.

Oasis Environmental. Final Site Characterization Report, Napaskiak Former BIA School Day Tanks. February 2012.

A site characterization was conducted in preparation for the construction of a new school on the site. The assessment included the sampling of the abandoned sewage lagoon and evaluation of the landfill suitability for disposal of impacted soil from the site.

The site at the time of the field activities included several buildings including the former school and utility building, and two former aboveground storage tank (AST) containment areas located south of the school and utility buildings.

The characterization activities included delineating the extent of soil impacts by advancing 25 test pits between four areas. These areas include three larger spill areas and one area not previously investigated.

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1) Area A: adjacent to the abandoned BIA school and utility building day tanks. The tanks were gone but cribbing remained. This area was sampled in the 2001 investigation (summarized above). DRO concentrations at Area A ranged from non-detect to 19,800 mg/kg. Location A2, collected at 2 feet bgs, was the only sample with a sample result above the cleanup level. Elevated headspace readings at location A5 suggested that it may also exceed cleanup levels.

2) Area B: west of the day tank area. The spill was a result of a release from BIA fuel piping.

DRO concentrations at Area B ranged from non-detect to 2,940 mg/kg. Location B3, collected at 0.5 feet bgs, was the only sample with a sample result above the cleanup level.

3) Area C: southwest of the day tank area at the former containment area. This was a result of cracked piping. The DRO levels ranged from non-detect to 15,600 mg/kg. The DRO results exceeded in each of the test pits except Locations C4 and C6, with samples from C3 and C7 exceeding the ingestion and inhalation cleanup levels. In addition, the samples from C2 (8 feet bgs), C3 (8 feet bgs), and C7 (8 feet bgs) also exceeded cleanup standards for benzene. Samples C2 and C7 (both 8 feet bgs) also exceeded ethylbenzene cleanup levels.

Sample C3 exceeded cleanup levels for polyaromatic hydrocarbons (PAHs) including naphthalene, 1-methylnaphthalene, and 2-methylnapthalene; and Sample C7 exceeded for naphthalene only.

4) Area D: south of the former school at the former AST containment area. This area had not been sampled prior to this investigation. The DRO levels ranged from non-detect to 26,100 mg/kg. Samples D1 (0.5 feet bgs), D2 (0.5 feet bgs), and D3 (2 feet bgs) exceeded the cleanup levels.

One additional spill was identified north of the utility building. This was a result of a leaking header valve.

Three wells are in Napaskiak. Two of the wells are greater than 500 feet from the site. Samples were collected from the community drinking water well located 800 feet west-southwest of the site. No volatile organic compounds (VOCs) were detected in the drinking water samples.

Three temporary wells were installed. The wells were installed between 3 feet bgs and 9 feet bgs.

The wells were slow to recharge so a no-flow sampling method was implemented. No sample was collected from WP-1 as the well did not recharge sufficiently to sample. DRO was detected above the 1.5 milligram per liter (mg/L) cleanup level in WP-2 (2.42 mg/L) and WP-3 (1.68 mg/L).

Since treatment and land disposal was being considered for the sewage solids from the former sewage lagoon, the lagoon was sampled as part of a bench-scale study to determine whether addition of alkali would be a practical treatment option. At the time of the field activities, the lagoon was 25 feet by 34 feet. The water depth in the lagoon ranged from 1.0 to 1.9 feet and sewage solid thickness ranged from 0.25 to 0.42 feet. The chemical oxygen demand (COD) and biochemical oxygen demand (BOD) indicated that the sewage solids have been exposed to the atmosphere for a long period of time and have undergone considerable degradation. The bench-

April 2025 4 scale study indicated that ¾ teaspoon of lime per 200 mL of sewage solids would be needed to treat the sewage wastes.

The report recommended in place landfarming to be the selected remedial alternative. The soil would be treated at depths up to 2 feet bgs and the contaminated soil would be mixed and amended with lime and fertilizer. The soil would be remixed once every two weeks over the course of one field season. This will allow building the proposed school on the BIA site and prevent direct contact to the contaminated soil.

ERM Alaska, Inc. Trench Installation for Preliminary Drum Assessment Report, Napaskiak, Alaska. December 2013.

A preliminary assessment of possible buried drums at the former BIA school site was conducted as part of the proposed new school building design project. In October 2012 the Lower Kuskokwim School District (LKSD) provided photographs of a drawing from March 1970 from the Department of Interior BIA Division of Plant Design and Construction. Notations on the drawing included “Existing Backfilled Pit – Verify.” A second drawing titled “Napaskiak Alaska, Water & Waste Treatment dated October 23, 1972 showed a “pit filled with 55 gal. drums” in the same area as the 1970 drawing. The drawing contained a note to “obtain fill from suitable remote area (not crest of hill) and backfill pit presently containing 55-gallon drums.”

Two additional field activities were summarized in the background section but no reports were available from the ADEC. In 2012 the LKSD constructed two in-place landfarm cells at the site in an effort to reduce DRO concentrations at locations that exceeded the 10,250 mg/kg cleanup standard during the 2011 site characterization activities. Eight tilling events were conducted over a four-week period; the tilling was at a depth of 18 inches bgs. At the completion of the tilling events, the soil sampling results were 3,098 and 2,964 mg/kg. In October 2012 the LKSD conducted a preliminary assessment of the potential drum pit. Five hand auger borings were advanced to 6 or 8 feet bgs. Slight petroleum odors were encountered between 1 and 2 feet bgs, 4 and 8 feet bgs. The soils were saturated and had a strong hydrocarbon odor at 8 feet bgs. No obstructions, drums, or metal of any kind were encountered.

As part of ERM’s preliminary assessment, two 50-foot long trenches were advanced in an “X” formation over the potential drum disposal area/pit. Each trench was excavated to a maximum depth of 8 feet bgs. Drums were encountered starting at approximately 2 to 3 feet bgs in the west to east trench. In the north to south trench, buried drums were encountered 1.5 to 3 feet bgs. Test pits were advanced outside the trenches to verify the terminus of the drum area. The drum pit area was estimated to be 16 feet (north to south) and 22 feet (east to west). Most of the drums appeared intact and were empty with some of them marked as “MONA LISA.” Project Mona Lisa referred to a military program that supplied facilities (particularly Aircraft Control and Warning sites) in Alaska. The number 62 was also marked and may be the year the drums were originally shipped to Alaska.

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Soil samples were collected from five locations within the drum pit assessment trenches. Only sample SO-2 contained analyte concentrations above cleanup levels. The DRO concentration was 272 mg/kg which exceeded the 250 mg/kg cleanup level.

2.0 INTERVIEWS AND RECORDS REVIEW

To obtain additional information about the site, TCC conducted interviews with locals knowledgeable about the site conditions and history and obtained a limited liability report.

2.1 Interviews

Napaskiak Tribal Council

Teddy Sipary, Napaskiak Tribal Administrator, was interviewed on July 22, 2024. Teddy has lived in Napaskiak for over 28 years. He noted that there was a flood in the community in early May that left the area that we are investigating underwater. When looking over our proposed location map, he noted that one of the proposed sample locations, Test Pit TP8, is usually under water in the fall due to the proximity to the slough. He noted that the former sewage lagoon was covered up and nothing else was done to remediate the lagoon prior to construction of the new school.

As for future remediation of the site, there is a gravel source in the community. However, keep in mind that if local resources are needed, moose hunting season is early September so local project support will be limited during that window.

City of Napaskiak

Joseph Amik, City Administrator, was interviewed on July 22, 2024. Joseph noted that there was a flood in early May that lasted four days. The flood waters extended throughout town, including across the school grounds. The water receded to the south and to the slough.

Joseph recalled the former BIA school had stored a lot of barrels of fuel. It was the only place he remembers in the community that had a power plant generator. Historically there has always been flooding in Napaskiak so he would not be surprised if contamination spread throughout the area because of those floodwaters.

2.2 Ownership Records Review

A Limited Liability Report was received by First American Title. The following ownership documents were obtained:

Napaskiak School Site

• Interim Conveyance recorded June 9, 1983: The surface estates of Section 9, Township 7N, Range 71W was conveyed to Napaskiak Incorporated pursuant to the Alaska Native Claims Settlement Act.

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• Plat 83-23: This plat was prepared for the Lower Kuskokwim School District to reflect the Napaskiak School site boundary. The site is 4.000 acres including overlap with the BIA School Lot and 3.581 acres without the BIA School Lot overlap.

• Quitclaim Deed recorded April 9, 2014: The State of Alaska Department of Education and Early Development granted the Z. John Williams Memorial School site (Plat 83-23) to the Lower Kuskokwim School District.

• Plat 2002-15 recorded August 1, 2002: The Napaskiak School site is shown as being 174,241 square feet.

• Public Use Easement recorded October 2, 2003: Napaskiak Incorporated granted the Native Village of Napaskiak an easement for the construction, maintenance and ongoing management of a boardwalk that intersects the Napaskiak School site.

BIA School Lot (Tracts A and B)

• Interim Conveyance recorded June 9, 1983: The surface estates of Section 9, Township 7N, Range 71W was conveyed to Napaskiak Incorporated pursuant to the Alaska Native Claims Settlement Act.

• Quitclaim Deed recorded June 10, 1989: The Bureau of Indian Affairs transfers the tract of unsurveyed land containing approximately 7.00 acres to the State of Alaska Department of Education.

• Plat 99-23 recorded December 20, 1999: BIA School Lot is shown as Tracts A and B. Tract A is 5.71 acres. Tract B is 0.298 acres. These lots are reflected per the Quitclaim recorded on June 10, 1989.

• Quitclaim Deed recorded April 9, 2014: The State of Alaska Department of Education and Early Development granted real property situated in the former Napaskiak BIA elementary school site Tract A (Plat 99-23) to the Lower Kuskokwim School District.

• Quitclaim Deed recorded February 8, 2000: The State of Alaska Department of Education and Early Development granted Tract B to the State of Alaska Department of Natural Resources for the use and benefit of the Department of the Army, Alaska Army National Guard.

• Plat 2002-15 recorded August 1, 2002: BIA School Lot is shown as Tracts A and B.

Copies of the documents referenced above are provided in Appendix B. The respective tracts are shown on Figure 2 (Appendix B).

3.0 CONTAMINANTS OF CONCERN AND APPLICABLE

REGULATIONS

The source or sources are suspected to be from documented releases from day tanks, a tank farm, fuel headers, and fuel lines. The constituents of potential concern (COPC) include the following petroleum-related compounds: DRO; volatile organic compounds (VOCs); and polyaromatic hydrocarbons (PAH).

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Soil and water samples collected during the field activities compared to the cleanup levels outlined in the following regulations:

• Soil: Method Two Under 40 Inch Zone Migration to Groundwater and Human Health and Inhalation levels outlined in Tables B1 and B2 in 18 Alaska Administrative Code (AAC) 75.341, Oil and Other Hazardous Substances Pollution Control (October 18, 2023)

• Groundwater: Table C in 18 AAC 75.345, Oil and Other Hazardous Substances Pollution Control (October 18, 2023)

4.0 SAMPLING METHODOLOGY

The field screening and analytical soil sampling methods used during the field activities are outlined below.

4.1 Soil Sampling Methods

Soil samples were collected using using an excavator. Each test pit was advanced to the water table and the soil characteristics (e.g., soil type, odor, sheen) were documented. The analytical soil sample was selected from the soil-water interface, unless there was indication of contamination at a different depth. Analytical soil samples were collected immediately upon retrieval and directly from the excavator bucket.

Soil samples were collected using clean spoons or disposable equipment and placed directly into clean laboratory-provided containers. Volatile samples were collected first and preserved with 25-milliter (mL) of methanol, per Alaska (AK) Methods.

4.2 Groundwater Development and Sampling Methods

A minimum of 24 hours after the wells were installed, the wells were developed. Prior to purging activities, depth to water and total well depths of each monitoring well were measured from the top of casing. This location was marked and at the highest point of the casing. An electronic water level meter was used to measure the depth to water, depth to product (if applicable), and total well depth to the nearest 0.01 foot. The measurements were recorded in the field notebook or log. The depths to water measurements were used to determine the groundwater flow direction and gradient.

Each well was developed using a surge block and disposable bailer. The surge block was used to surge the formation and the bailer was used to remove the water. This surge-purge process was conducted until 10 well volumes had been removed (Wells MW3 and MW5) or until the well purged dry (Wells MW1, MW2, MW4). For wells that purged dry, the wells were allowed to refill with formation water. If the recovery was too slow, one casing of potable water was added to the well and the well was surged and purged until the well went dry again and the development was considered complete. The purge water was containerized for later treatment.

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The monitoring wells were purged using low-flow sampling methods per the Environmental Protection Agency’s 2010 Low Stress (low flow) Purging and Sampling Procedure for the Collection of Groundwater Samples from Monitoring Wells. A decontaminated positive displacement submersible mini-monsoon pump and disposable tubing were used to purge and collect the groundwater monitoring well samples. When samples were being collected, the pump was initially placed to be within 1 foot of the water surface. Samples were collected by removing the inflow hose from the flow-through cell and filling laboratory-provided sample containers directly from the tube; first hydrochloric-acid preserved containers for VOC analysis, then unpreserved containers for PAH analysis, and finally hydrochloric acid-preserved containers for DRO analysis. Purge water was collected in five-gallon buckets. The Low Flow Sampling Data Logs are provided in Appendix C.

5.0 FIELD ACTIVITIES

The field activities were conducted in July and October 2024. The July 2024 field activities included a site characterization to delineate the lateral and vertical extent of contamination, gather current site condition information to evaluate potential remedial options for the site, as well as install and conduct groundwater monitoring of nine wells to determine groundwater conditions.

The October 2024 field activities included collection of groundwater samples from the site’s wells.

Field notes of the field activities are provided in Appendix C. Photographs of the field activities are provided in Appendix D.

Shayla Marshall, TCC, and Paul Fallgren of Advanced Environmental Technologies LLC were the Qualified Environmental Professionals (QEPs) collecting the samples and directing the field work. Their resumes are provided in Appendix E. The level loop survey and drone mapping were conducted by Dale Erickson of TCC and supported by Cynthia Erickson.

5.1 Work Plan Variances

In general, the work followed the ADEC-approved work plan as written, with the following exceptions:

• Headspace samples were unable to be collected. The photoionization detector (PID) was accidentally left off the flight by the airlines and, therefore, did not make it to the site in time.

• The proposed sample location downgradient of the header release (TP8) was not advanced.

Based on conversations with the local community, this area is regularly underwater in the fall.

• Due to the availability of local excavator equipment and operator, 2-inch PVC pre-pack monitoring wells were installed instead of 3/4-inch Solinist stainless steel drive-point piezometers. This variance was communicated to the ADEC’s project manager, Bill O’Connell on July 19, 2024 and approved on the same date.

• Bailers were used instead of a peristaltic pump during the July 2024 field activities due to mechanical issues with the pump.

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5.2 Site Characterization Activities

The site characterization activities included advancing test pits, installing monitoring wells, developing and sampling the newly installed permanent monitoring wells, and conducting a survey of the new wells.

5.2.1 Test Pits

A total of 10 test pits were advanced July 22, 2024. An excavator was used to advance each test pit with each test pit advanced to the water table or to permafrost. The purpose of the test pits were to assess the current soil conditions within the former source area and surrounding areas, as indicated on Figure 4. The test pits focused on the following areas to update extents, depths, and volumes of contamination:

• Downgradient of sample locations from 2011/2013 containing concentrations above cleanup levels: Test Pits TP1, TP3, TP6, TP7, TP9, TP10, TP11

• Previous well point locations, including those where DRO concentrations exceeded cleanup levels: Test Pits TP2, TP5, and TP8

• Former header leak: Test Pit TP4

In addition, a site reconnaissance of the area was conducted prior to advancing the test pits to identify if there are additional areas needing investigation or indicative releases since the previous investigation work at the site.

Ten soil samples and one duplicate were submitted for analysis. The sample was selected from the soil-water interface and/or if there was indication of impact based on field observations (e.g., staining or odor).

Test Pit locations are shown in Figure 4 and global positioning system (GPS) location information is provided in Table 1. The test pits were advanced to groundwater which was encountered at between 1-7.5 bgs.

Table 1 – GPS Coordinates of Sample Locations

Well ID Latitude Longitude

MW1/TP1 60.7077418 -161.7630315

MW2/TP2 60.7076141 -161.7639312

MW3/TP3 60.7080600 -161.7637957

MW4/TP4 60.7084485 -161.7633505

MW5/TP5 60.7079984 -161.7617360

TP6 60.7079151 -161.7627485

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TP7 60.7078446 -161.7633803

TP9 60.7083445 -161.7629700

TP10 60.7079966 -161.7630002

TP11 60.7083254 -161.7633012

5.2.2 Monitoring Well Installation

Five monitoring wells were installed on July 22, 2024. The wells were installed in the following locations, as shown on Figure 5:

• Upgradient and downgradient from the Old BIA Tank Farm: Monitoring Wells MW1 and

MW4

• In the general vicinity of the previous well point locations where contamination was encountered: Monitoring Wells MW2 and MW5

• Between the two previous well points (WP-2 and WP-3): Monitoring Well MW3

These wells were placed within the test pits advanced and sampled. An excavator was used to advance the test pit until water was encountered at which the test pit was advanced an additional 5 feet into the water column or until frozen soil was encountered. The well comprised of a 2-inch diameter 5-foot prepack PVC screen connected to a blank PVC riser. Each well was cut to ground surface and completed with a well plug and flush monument.

5.2.3 Water Level Measurements and Flow Direction

Water level measurements were collected for the site’s wells on July 23, 2024, prior to well purging and sampling. The water level measurements are provided in Table 2.

Table 2 – July 2024 Water Level Measurements

Well ID

Total Well

Depth (ft)

Total Well

Elevation (from toc)

Depth to Water (ft btoc)

Top of Casing (bgs)

Depth to Water (ft bgs)

Water Elevation

(ft bgs)

MW1 6.60 10.00 2.25 0.20 2.45 7.75

MW2 6.10 10.61 2.00 0.20 2.2 8.61

MW3 7.50 11.79 4.42 0.20 4.62 7.37

MW4 6.50 11.17 4.92 0.20 5.12 6.25

MW5 5.20 11.01 1.00 0.10 1.10 10.01

A level loop survey was conducted for each of the site’s wells. The level loop survey collected the top of casing elevations of the wells in order to calculate the site’s groundwater flow direction and gradient. The elevation data was collected to the nearest 0.01 feet, and the elevation is shown in Table 2 (above). As shown on Figure 5, the shallow groundwater at the site prior to well development appears to flow to the northwest.

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5.3 Fall 2024 Monitoring Well Sampling

Each of the monitoring wells were sampled during the Fall 2024 event. Water level measurements were conducted prior to purging/sampling on October 3, 2024. The water level measurements are listed below. Note, several of the wells appeared to have jacked up or sank since the July 2024 event, likely due to the high-water table across the site. As shown on Figure 6, the groundwater flow direction appeared to be to the west, noting these water elevations are based on the well conditions from July 2024.

Table 3 – October 2024 Water Level Measurements

Well ID

Total Well

Depth (ft)

Total Well

Elevation (from toc)

Depth to Water (ft btoc)

Top of Casing (bgs)

Depth to Water (ft bgs)

Water Elevation

(ft bgs)

MW1 6.60 10.00 2.33 0.60 2.93 7.67

MW2 6.10 10.61 3.10 0.15 3.25 7.51

MW3 7.50 11.79 4.57 0.10 4.67 7.22

MW4 6.50 11.17 3.85 0.15 4.00 7.32

MW5 5.20 11.01 1.00 0.00 1.00 10.01

5.4 Decontamination Procedures

Decontamination procedures were implemented to minimize the potential for cross-contamination at the site. The re-usable spoons for soil sampling, water sampling pump, product level/water level meter and water quality instrument were decontaminated using water and Alconox and rinsed using a combination of potable and deionized water. The pump was placed in the Alconox-water bucket and ran for 1-2 minutes prior to placing it in the potable water and ran for another 1-2 minutes. The pump was then rinsed with deionized water prior to using for the next monitoring well. Dedicated tubing was used for each well and disposed of after use. The water generated from the decontamination was containerized and treated with granulated activated carbon (GAC) onsite.

6.0 SAMPLING RESULTS

The samples were submitted to SGS North America, Inc. (SGS) laboratory in Anchorage, Alaska for sample analysis. The soil and groundwater results are described in further detail below.

6.1 Subsurface Conditions

Surface soils at the site consisted primarily of brown peat within the top foot. Gray to brown silty sand or sandy silt were encountered beneath the peat. Frozen soils were encountered in Test Pits TP1, TP4, TP9, and TP11 between 3 to 7.5 feet bgs, noting three of these test pits were located just north of the existing school building. With the exception of Test Pit TP5, water was encountered between 4 and 7.5 feet below ground surface. The area around Test Pit TP5 was marshy and water was encountered within the top foot.

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Field observations including the presence of organics, debris, and petroleum odors were noted in several test pits. Organics were encountered in Test Pits TP3 and TP10. Geofabric was encountered at 1 feet bgs in Test Pit TP7. Petroleum odor was noted in the soils at Test Pits TP4, TP5, TP6, TP7, TP9, and TP11.

6.2 Test Pit Soil Results

Samples were collected and submitted for analysis from each test pit. Exceedances in the ADEC Method 2 Migration to Groundwater Cleanup (MTG) level were reported in each sample except TP1, TP3, and TP10. A DRO concentration greater than Maximum Allowable Concentrations was also reported from the primary sample from Test Pit TP4.

VOCs and PAHs were also reported at concentrations greater than the ADEC MTG cleanup level.

Naphthalene was reported in the samples from Test Pits TP2, TP4 and its duplicate, TP5, TP6, TP7, TP9, and TP11 at concentrations greater than cleanup levels. Additionally, cleanup standard exceedances of 1-methylnaphthalene, 2-methylnaphthalene, and 1,2,4-trimethylbenzene were reported in the samples from Test Pits TP4 (including the duplicate) and TP9. Test Pit TP4 also contained 1,3,5-trimethylbenzene, benzene, ethylbenzene, and xylenes concentrations greater than cleanup levels.

Detectable analytical results are listed below in Table 4.

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Table 4 – Detected Soil Analytical Results

Analyte Analysis Unit Cleanup Level* TP1 TP2 TP3 TP4 TP24 TP5 TP6 TP7 TP9 TP10 TP11 STB

Sample Depth - Ft - 5.5 4 5 7 1 3.5 3.5 5 4 6 3 - Diesel Range Organics AK102 mg/kg 250 20.0 U 20.5 U 19.1 U 19100 8340 371 40.1 49.6 5750 29.8 207 - Residual Range Organics AK103 mg/kg 11000 106 J 132 J 96.0 U 346 194 J 1420 246 110 J 236 271 184 - Polyaromatic Hydrocarbons

1-Methylnaphthalene 8270E SIM ug/kg 410 25.0 U 25.6 U 23.9 U 30400 16300 19.4 J 25.5 U 10.7 J 15300 10.2 J 148 - 2-Methylnaphthalene 8270E SIM ug/kg 1300 25.0 U 25.6 U 23.9 U 45400 28800 28.8 J 25.5 U 10.7 J 22400 13.4 J 239 - Acenaphthene 8270E SIM ug/kg 37000 25.0 U 25.6 U 23.9 U 703 373 30.1 U 25.5 U 24.8 U 519 26.3 U 26.2 U - Benzo(a)Anthracene 8270E SIM ug/kg 700 25.0 U 25.6 U 23.9 U 509 U 246 U 30.1 U 25.5 U 24.8 U 138 J 11.9 J 26.2 U - Benzo[a]pyrene 8270E SIM ug/kg 1900 25.0 U 25.6 U 23.9 U 509 U 246 U 30.1 U 25.5 U 24.8 U 267 U 14.3 J 26.2 U - Benzo[b]Fluoranthene 8270E SIM ug/kg 20000 25.0 U 25.6 U 23.9 U 509 U 246 U 30.1 U 25.5 U 24.8 U 104 J 38.2 26.2 U - Benzo[g,h,i]perylene 8270E SIM ug/kg 15000000 25.0 U 25.6 U 23.9 U 509 U 246 U 30.1 U 25.5 U 24.8 U 267 U 11.1 J 26.2 U - Benzo[k]fluoranthene 8270E SIM ug/kg 190000 25.0 U 25.6 U 23.9 U 509 U 246 U 30.1 U 25.5 U 24.8 U 267 U 11.0 J 26.2 U - Chrysene 8270E SIM ug/kg 600000 25.0 U 25.6 U 23.9 U 509 U 246 U 30.1 U 25.5 U 24.8 U 267 U 32.1 J 26.2 U - Fluoranthene 8270E SIM ug/kg 590000 25.0 U 25.6 U 23.9 U 509 U 246 U 30.1 U 25.5 U 24.8 U 678 26.3 U 26.2 U - Fluorene 8270E SIM ug/kg 36000 25.0 U 25.6 U 23.9 U 1940 1020 30.1 U 25.5 U 24.8 U 830 26.3 U 26.2 U - Indeno[1,2,3-c,d] pyrene 8270E SIM ug/kg 65000 25.0 U 25.6 U 23.9 U 509 U 246 U 30.1 U 25.5 U 24.8 U 267 U 9.46 J 26.2 U - Naphthalene 8270E SIM ug/kg 38 20.0 U 20.5 U 19.1 U 13700 9470 14.4 J 7.07 J 24.1 J 4530 21.1 U 67.2 - Phenanthrene 8270E SIM ug/kg 39000 25.0 U 25.6 U 23.9 U 1030 505 30.1 U 25.5 U 24.8 U 738 26.3 U 26.2 U - Pyrene 8270E SIM ug/kg 87000 25.0 U 25.6 U 23.9 U 509 U 246 U 30.1 U 25.5 U 24.8 U 460 26.3 U 26.2 U - Other PAHs 8270E SIM ug/kg varies ND ND ND ND ND ND ND ND ND ND ND -

Volatile Organic Compounds (VOCs) 1,2,4-Trimethylbenzene SW8260D ug/kg 610 128 U 390 49.6 JB 16200 10700 366 J+ 159 U 177 J 1410 176 U 155 U 77.4 J 1,3,5-Trimethylbenzene SW8260D ug/kg 660 31.9 U 104 29.0 JB 7280 5000 142 J+ 39.8 U 40.8 JB 403 44.0 U 38.8 U 38.1 4-Isopropyltoluene SW8260D ug/kg - 102 U 199 91.5 U 910 778 143 U 128 U 128 U 487 141 U 125 U 60.8 U Benzene SW8260D ug/kg 22 15.9 U 18.4 U 14.3 U 39.5 39.9 22.4 U 19.9 U 20.0 U 27.2 U 22.0 U 19.4 U 9.52 U Ethylbenzene SW8260D ug/kg 130 31.9 U 38.7 J 28.7 U 1290 661 44.7 U 39.8 U 24.4 J 46.8 J 44.0 U 38.8 U 19.0 U Isopropylbenzene SW8260D ug/kg 5600 31.9 U 36.8 U 28.7 U 2100 949 30.3 J 39.8 U 21.0 J 78.6 44.0 U 38.8 U 19.0 U Methylene chloride SW8260D ug/kg 330 128 U 147 U 49.6 J 173 U 137 U 179 U 66.5 J 160 U 218 U 176 U 155 U 75.8 U

Continued on following page

April 2025 14

Table 4 – Detected Soil Analytical Results (continued)

Analyte Analysis Unit Cleanup Level* TP1 TP2 TP3 TP4 TP24 TP5 TP6 TP7 TP9 TP10 TP11 STB

Volatile Organic Compounds (VOCs) - Continued n-Butylbenzene SW8260D ug/kg 23000 31.9 U 276 28.7 U 3580 1870 90.8 39.8 U 39.9 U 625 44.0 U 38.8 U 13.1 J n-Propylbenzene SW8260D ug/kg 9100 31.9 U 88.3 28.7 U 1650 751 33.5 J 39.8 U 42.2 J 165 44.0 U 38.8 U 19.0 U Naphthalene SW8260D ug/kg 38 31.9 U 254 28.7 U 9730 5970 389 J+ 54.7 J+ 49.0 J 1960 44.0 U 53.3 J+ 19.3 J sec-Butylbenzene SW8260D ug/kg 42000 31.9 U 50.2 28.7 U 996 607 24.9 J 39.8 U 18.6 J 296 44.0 U 38.8 U 19.0 U tert-Butylbenzene SW8260D ug/kg 11000 31.9 U 36.8 U 28.7 U 224 148 44.7 U 39.8 U 39.9 U 22.9 J 44.0 U 38.8 U 19.0 U Toluene SW8260D ug/kg 6700 31.9 U 17.3 J 28.7 U 33.9 J 31.8 J 44.7 U 39.8 U 39.9 U 26.3 J 44.0 U 38.8 U 19.0 U Xylenes (total) SW8260D ug/kg 1500 95.3 U 158 86.3 U 9050 9120 117 J+ 119 U 120 U 187 J 132 U 116 U 30.5 J Other VOCs SW8260D ug/kg varies ND ND ND ND ND ND ND ND ND ND ND ND

Notes:

* 18 AAC 75 Table B1 and B2 Migration to Groundwater (MTG) Cleanup Level (October 18, 2023) ~ Duplicate of preceeding sample mg/kg Milligram per kilogram ug/kg Microgram per kilogram 158 Analyte detected below MTG Cleanup Level 9050 Analyte detected above MTG Cleanup Level 117 J Analyte was detected at an estimated concentration of 117 ug/kg, less than its action level.

19100 Concentration exceeds the DRO (12,500 mg/kg) Maximum Allowable Concentration (October 18, 2023)

31.9 U Analyte non-detect

1.02 U Analyte non-detect; detection limit above cleanup level

ND Non-detect J+ Concentration may be detected due to possible laboratory carryover

- Not sampled or not applicable

April 2025 15

6.3 July 2024 Groundwater Monitoring Results

The site wells were sampled on July 23, 2024. Detectable concentrations of DRO, several PAHs, and several VOCs were reported, however all concentrations were less than the cleanup level.

Note, Well MW4 was not sampled due to visible product on the purgewater at the time of development. Detectable analytical results are listed in Table 5.

Table 5 – Detected July 2024 Water Analytical Results

Analyte Analysis Unit Cleanup Level* MW1 MW2 MW3 MW5 MW25~ Trip

Blank

Diesel Range Organics AK102 LV mg/L 1.5 0.915 0.506 J 0.621 0.738 0.887 - Polyaromatic Hydrocarbons (PAHs)

1-Methylnaphthalene 8270E SIM ug/L 11 0.00695 J 2.36 0.0121 J 0.143 0.167 - 2-Methylnaphthalene 8270E SIM ug/L 36 0.00783 J 3.10 0.0158 0.0783 0.0768 - Acenaphthene 8270E SIM ug/L 530 0.00990 U 0.0399 0.00967 U 0.00990 U 0.0409 - Anthracene 8270E SIM ug/L 43 0.00990 U 0.00910 J 0.00967 U 0.00990 U 0.00997 U - Benzo(a)Anthracene 8270E SIM ug/L 0.3 0.00990 U 0.00966 J 0.00967 U 0.00506 J 0.00997 U - Benzo[b]Fluoranthene 8270E SIM ug/L 2.5 0.00990 U 0.0133 J 0.00967 U 0.00990 U 0.00997 U - Benzo[g,h,i]perylene 8270E SIM ug/L 0.26 0.00990 U 0.0143 J 0.00967 U 0.00990 U 0.00997 U - Benzo[k]fluoranthene 8270E SIM ug/L 0.8 0.00990 U 0.0222 0.00967 U 0.00990 U 0.00997 U - Chrysene 8270E SIM ug/L 2 0.00990 U 0.0104 J 0.00967 U 0.00521 J 0.00997 U - Dibenzo[a,h]anthracene 8270E SIM ug/L 0.25 0.00394 U 0.00845 0.00386 U 0.00394 U 0.00399 U - Fluoranthene 8270E SIM ug/L 260 0.00990 U 0.0739 0.00967 U 0.00990 U 0.00997 U - Fluorene 8270E SIM ug/L 290 0.00534 J 0.0143 J 0.00967 U 0.0473 0.0493 - Indeno[1,2,3-c,d] pyrene 8270E SIM ug/L 0.19 0.00990 U 0.0169 0.00967 U 0.00990 U 0.00997 U - Naphthalene 8270E SIM ug/L 1.7 0.0197 U 1.02 0.0105 J 0.188 0.239 - Phenanthrene 8270E SIM ug/L 170 0.00996 J 0.0121 J 0.00867 J 0.0171 J 0.0227 J - Pyrene 8270E SIM ug/L 120 0.00990 U 0.0352 0.00967 U 0.00535 J 0.00599 J - Other PAHs 8270E SIM ug/L varies ND ND ND ND ND -

Volatile Organic Compounds (VOCs) 1,2,4-Trimethylbenzene SW8260D ug/L 56 0.750 U 6.16 0.750 U 1.14 1.18 0.750 U 1,3,5-Trimethylbenzene SW8260D ug/L 60 0.750 U 2.10 0.750 U 0.920 J 0.940 J 0.750 U 2-Butanone (MEK) SW8260D ug/L 5600 27.1 5.04 J 4.19 J 7.50 U 7.50 U 7.50 U 4-Isopropyltoluene SW8260D ug/L - 0.750 U 5.64 0.750 U 0.470 J 0.470 J 0.750 U Benzene SW8260D ug/L 4.6 0.300 U 0.150 J 0.300 U 0.300 U 0.300 U 0.300 U Dichlorodifluoromethane SW8260D ug/L 200 0.750 U 0.750 U 0.750 U 17.0 14.8 0.750 U n-Butylbenzene SW8260D ug/L 1000 0.750 U 1.35 0.750 U 0.750 U 0.750 U 0.750 U n-Propylbenzene SW8260D ug/L 660 0.750 U 0.820 J 0.750 U 0.750 U 0.750 U 0.750 U Naphthalene SW8260D ug/L 1.7 0.750 U 2.86 0.750 U 1.30 1.32 0.750 U sec-Butylbenzene SW8260D ug/L 2000 0.750 U 0.720 J 0.750 U 0.750 U 0.750 U 0.750 U Toluene SW8260D ug/L 1100 2.49 0.750 U 0.750 U 0.750 U 0.750 U 0.750 U Other VOCs SW8260D ug/L varies ND ND ND ND ND ND

Notes:

* 18 AAC 75 Table C Groundwater Cleanup Level (October 18, 2023) ~ Duplicate of preceding sample

April 2025 16 mg/L Milligram per liter ug/L Microgram per liter

0.915 Analyte detected below Table C Cleanup Level

2.86 Analyte detected above Table C Cleanup Level

0.930 J Analyte was detected at an estimated concentration of 0.930 mg/kg, less than its action level.

0.750 U Detection limit greater than the Cleanup Level

6.4 October 2024 Groundwater Monitoring Results

The site wells five wells were sampled using low-flow methods on October 3, 2024. Notable observations in the purgewater from the wells are as follows:

• MW1: An organic sheen was noted on the purgewater.

• MW2: The well purged dry after 3 minutes of purging. The well recovered, but due to the limited water column the full volume of sample could not be obtained for the PAH analysis.

• MW3: An organic, sewage-like odor was noted on the purgewater. This purgewater also had a greasy, orange-tan appearance.

• MW4: A strong petroleum odor and slight sheen was noted in the purgewater. While filling the VOC sample containers, the water effervesced upon contact with the hydrochloric acid preservative.

• MW5: Orange sludge/residue was observed on the top of the water; the water table was within 1 foot of the ground surface.

Concentrations of DRO, naphthalene, 1,2,4-trimethylnaphthalene, and/or 1,3,5-trimethylnapthalene were reported in one of more wells at concentrations greater than the cleanup level. The highest concentrations were reported in Well MW3. Based on the field observations, the elevated concentrations in Wells MW1 and MW3 may be partly biogenic in nature as neither of the respective soil samples contained concentrations greater than cleanup level and no other indication (e.g., petroleum odor or petroleum sheen) were noted on the purgewater during either sampling event. Well MW5 did not contain concentrations greater than cleanup levels.

Detectable analytical results are listed in Table 6.

April 2025 17

Table 6 – Detected October 2024 Water Analytical Results

Analyte Analysis Unit Cleanup Level* MW1 MW2 MW3 MW4 MW5 MW25~ WTB Diesel Range Organics AK102 LV mg/L 1.5 3.35 0.550 J 87.3 5.53 1.03 1.18 - Polyaromatic Hydrocarbons (PAHs)

1-Methylnaphthalene 8270E SIM ug/L 11 0.0334 BJ- 0.0297 B 14.6 J- 0.0125 J-B 0.0887 0.138 J- - 2-Methylnaphthalene 8270E SIM ug/L 36 0.0273 BJ- 0.0201 B 7.49 J- 0.0151 BJ- 0.0905 0.126 J- - Acenaphthene 8270E SIM ug/L 530 0.00483 J- 0.00608 J 0.103 UJ- 0.0109 UJ- 0.00688 J 0.00632 J- - Benzo[a]pyrene 8270E SIM ug/L 0.25 0.00409 UJ- 0.00577 U 0.0410 UJ- 0.00255 J- 0.00375 U 0.00409 UJ- - Dibenzo[a,h]anthracene 8270E SIM ug/L 0.25 0.00409 UJ- 0.00577 U 0.0410 UJ- 0.00285 J- 0.00375 U 0.00409 UJ- - Fluoranthene 8270E SIM ug/L 260 0.0103 UJ- 0.0144 U 0.103 UJ- 0.00538 J- 0.00938 U 0.0103 UJ- - Fluorene 8270E SIM ug/L 290 0.0116 J- 0.0144 U 0.857 J- 0.00759 J- 0.0147 0.0146 J- - Naphthalene 8270E SIM ug/L 1.7 0.0125 J- 0.0374 J 7.46 J- 0.0109 J- 0.111 0.15 J- - Phenanthrene 8270E SIM ug/L 170 0.0114 J-B 0.0289 U 0.295 J- 0.0155 J-B 0.00924 JB 0.0205 UJ- - Pyrene 8270E SIM ug/L 120 0.0103 UJ- 0.0144 U 0.103 UJ- 0.00479 J- 0.00938 U 0.0103 UJ- - Other PAHs 8270E SIM ug/L varies ND ND ND ND ND ND -

Volatile Organic Compounds (VOCs) 1,2,4-Trimethylbenzene SW8260D ug/L 56 0.750 U 2.5 97.7 0.750 U 0.748 J 0.479 J 0.750 U 1,3,5-Trimethylbenzene SW8260D ug/L 60 0.750 U 0.760 J 72.8 0.750 U 0.610 J 0.407 J 0.750 U 2-Butanone (MEK) SW8260D ug/L 5600 5.41 J 7.50 U 12.6 5.70 J 8.70 J 9.15 J 7.50 U 4-Isopropyltoluene SW8260D ug/L - 0.750 U 1.07 4.97 0.750 U 0.750 U 0.750 U 0.750 U Benzene SW8260D ug/L 4.6 0.300 U 0.143 J 4.22 0.300 U 0.300 U 0.300 U 0.300 U Dichlorodifluoromethane SW8260D ug/L 200 0.750 U 0.750 U 0.750 U 0.750 U 3.4 4.3 0.750 U Ethylbenzene SW8260D ug/L 15 0.750 U 0.750 U 8.96 0.750 U 1.27 0.799 J 0.750 U Isopropylbenzene SW8260D ug/L 450 0.750 U 0.750 U 4.05 0.750 U 0.750 U 0.750 U 0.750 U n-Butylbenzene SW8260D ug/L 1000 0.750 U 2.25 0.750 U 0.750 U 0.750 U 0.750 U 0.750 U n-Propylbenzene SW8260D ug/L 660 0.750 U 0.463 J 4.64 0.750 U 0.750 U 0.750 U 0.750 U Naphthalene SW8260D ug/L 1.7 0.750 U 1.77 42.9 0.750 U 0.796 J 0.561 J 0.750 U sec-Butylbenzene SW8260D ug/L 2000 0.750 U 0.467 J 3.45 0.750 U 0.750 U 0.750 U 0.750 U tert-Butylbenzene SW8260D ug/L 690 0.750 U 0.750 U 1.38 0.750 U 0.750 U 0.750 U 0.750 U Toluene SW8260D ug/L 1100 15.7 0.750 U 0.750 U 7.51 192 119 0.750 U Xylenes (total) SW8260D ug/L 190 2.25 U 2.25 U 189 2.25 U 2.25 U 2.25 U 2.25 U Other VOCs SW8260D ug/L varies ND ND ND ND ND ND ND

April 2025 18

Notes:

* 18 AAC 75 Table C Groundwater Cleanup Level (October 18, 2023) ~ Duplicate of preceding sample mg/L Milligram per liter ug/L Microgram per liter

15.7 Analyte detected below Table C Cleanup Level

1.77 Analyte detected above Table C Cleanup Level

0.0374 J Analyte was detected at an estimated concentration of 0.0374 mg/kg, less than its action level.

J- Analyte concentration is considered biased low due to bubbles in VOA vials exceeding 6mm

B Analyte concentration is considered a high estimated value due to contamination being present in the method blank

7.0 QUALITY CONTROL REVIEW

ADEC Laboratory Data Review Checklists were completed for the SGS reports. The laboratory reports and checklists are included in Appendix F. The following is a summary of the quality control (QC) issues affecting data quality or usability.

7.1 SGS Report 1243966 Soil Samples

The following QC issue and the effect on data quality or usability was noted:

• The LOQ for Pyrene, 1,1,1,2-Tetrachloroethane, 1,1,2,2-Tetrachloroethane, 1,1,2- Trichloroethane, 1,2,3-Trichlorobenzene, 1,2,3-trichloropropane, 1,2-Dibromoethane, 1,4- Dichlorobenzene, 2-Hexanone, Benzene, Bromodichloromethane, Bromomethane, Carbon tetrachloride, Chloroform, cis-1,3-Dichloropropene, Dibromochloromethane, Dibromomethane, Hexachlorobutadiene, Naphthalene, trans-1,3-Dichloropropene, Trichloroethene, and Vinyl chloride limits of quantitation (LOQ) greater than the cleanup level for one or more samples.

• Detections of multiple analytes in Samples TP5, TP6, TP10, and TP11 may be associated with possible carryover. These affected results are flagged with a J+ in the sample summary tables.

• Reported concentrations of 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, o-xylene, and naphthalene were above the calibration range in Samples TP4 and TP24. The samples could not be re-analyzed due to hold time. Since Samples TP4 and TP24 both contained concentrations well above cleanup levels for 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene and other analytes, the sample results are considered usable for the project purpose.

• The relative percent difference (RPD) is above the recommended 50% for DRO, RRO, 1-methylnaphthalene, acenaphthene, fluorene, phenanthrene, ethylbenzene, isopropylbenzene, n-butylbenzene, and n-propylbenzene in primary/duplicate soil samples

April 2025 19

TP4/TP24. Samples TP4 and TP24 were both well above cleanup levels in several analytes which may attribute to the variability between the primary and duplicate samples. For this project purpose, the higher of the concentrations is used.

7.2 SGS Report 1243965 July Groundwater Samples

The following QC issues and the effect on data quality or usability were noted:

• The LOQ for 1,2,3-trichloropropane exceeded the ADEC cleanup level. Since the samples did not exceed cleanup levels for other analytes, the data is considered usable for the project purpose of determining if contamination is present or absent in the site’s groundwater as of July 2024.

• Estimated (j-flagged) concentrations of 2-methylnaphthalene was reported in the method blank. Project samples that contained concentrations within 10 times the method blank concentration were flagged with a “B” in the summary tables and are considered a high estimated value.

7.3 SGS Report 1245835 October Groundwater Samples

The following QC issues and the effect on data quality or usability were noted:

• The VOA vials from MW1, MW3, MW4, and MW25 contained greater than 6mm headspace. The VOC concentrations may be biased low. The impacted sample results are flagged as a J- in Table 6.

• Estimated (j-flagged) concentrations of 1-methylnaphthalene, 2-methylnaphthalene, and phenanthrene were reported in the method blank. Project samples that contained concentrations within 10 times the method blank concentration were flagged with a “B” in the summary tables and are considered a high estimated value.

• The LOQ for 1,2,3-trichloropropane exceeded the ADEC cleanup level. Since the samples exceeded cleanup levels for other analytes, the data is considered usable for the project purpose of determining if contamination is present or absent in the site’s groundwater as of July 2024.

• The RPD is above the recommended 30% for 1-methylnaphthalene, 2-methylnaphthalene, naphthalene, 1,2,4-trimethylbenzene, and 1,3,5-trimethylbenzene in water samples MW5/MW25. These analytes did not exceed cleanup levels in either the primary or duplicate samples. Therefore, the elevated RPD is not likely to affect data usability.

8.0 DISCUSSION

A discussion of the results from the July and October 2024 sample results are described in further detail below.

April 2025 20

8.1 Soil Sampling Discussion

Soil samples were collected from the test pits advanced across the site. Test pit samples focused on identifying downgradient extents from previously identified contaminated areas, confirming locations that contained DRO concentrations above cleanup levels in the past, and determining concentrations at a former header leak.

Naphthalene concentrations exceeding cleanup levels were reported in the samples collected adjacent to the previously impacted samples. Test Pits TP6 and TP7 were advanced in the vicinity of Area C (Tank Farm Piping Release) and Area D (Tank Farm) where an insitu landfarm cell was installed in 2012. Historically samples from these areas also exceeded the benzene, DRO, 1-methylnaphthalene, and 2-methylnapthalene cleanup levels. However, due to the exceedance of naphthalene only in the two test pits and concentrations less than cleanup levels in the upgradient (TP1) and downgradient (TP3 and TP10) test pits, the contamination in these areas appears to be limited to naphthalene and defined.

Concentrations of naphthalene and/or DRO were also reported in test pits advanced near previous well point locations.