2025_Napaskiak_Report_0001.pdf

FINAL

2025 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

February 2026

2025 Site Characterization Report – FINAL Napaskiak Former BIA School Day Tanks; ADEC File No. 2433.38.004 February 2026 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

February 2026 ii

TABLE OF CONTENTS

1.0 SITE DESCRIPTION AND BACKGROUND

1.1 Project Purpose and Objectives

1.2 Site Location

1.3 Land Ownership

1.4 Background

2.0 CONTAMINANTS OF CONCERN AND APPLICABLE

REGULATIONS

3.0 SAMPLING METHODOLOGY

3.1 Soil Sampling Methods

3.2 Groundwater Sampling Methods

4.0 FIELD ACTIVITIES

4.1 Work Plan Variances

4.2 Site Characterization Activities

4.2.1 Test Pits

4.2.2 Monitoring Well Maintenance and Sampling

4.2.3 Water Level Measurements and Flow Direction

4.3 Decontamination Procedures

5.0 SAMPLING RESULTS

5.1 Subsurface Conditions

5.2 Test Pit Soil Results

5.3 Groundwater Monitoring Results

6.0 QUALITY CONTROL REVIEW

6.1 SGS Report 1254388 Soil Samples

6.2 SGS Report 1254357 Groundwater Samples

7.0 DISCUSSION

7.1 Soil Sampling Discussion

7.2 Groundwater Monitoring Discussion

7.3 Conceptual Site Model Discussion

8.0 INVESTIGATIVE DERIVED WASTE MANAGEMENT

9.0 CONCLUSIONS AND RECOMMENDATIONS

10.0 REFERENCES

February 2026 iii

TABLES

Table 1 – GPS Coordinates of Sample Locations Table 2 – August 2025 Water Level Measurements Table 3 – Detected 2025 Soil Analytical Results Table 4 – Detected 2025 Water Analytical Results

FIGURES

Figure 1 – Vicinity Map Figure 2 – Project Area Figure 3 – Historical Sample Locations Figure 4 – 2025 Soil Sample Locations Figure 5 – August 2025 Monitoring Well Samples

APPENDICES

Appendix A – Figures Appendix B – Field Notes Appendix C – Photo Pages Appendix D – SGS Laboratory Reports and Laboratory Data Review Checklists Appendix E – Human Health Conceptual Site Model Graphic Form and Human Health

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

February 2026 iv

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 SGS SGS North America TCC Tanana Commercial Company LLC VOC Volatile Organic Compound

February 2026 1

FINAL

2025 Site Characterization Report

ADEC File No. 2433.38.004

This report outlines the 2025 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 April 23, 2025 Contract No. 140A0525P0021 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.

• 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.

1.3 Land Ownership

The site was conveyed from the BIA to the State of Alaska Department of Education in 1989. In 2014 the land was quitclaimed to the Lower Kuskokwim School District, the current owner of the property.

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1.4 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.

February 2026 3

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-

February 2026 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.

February 2026 5

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.

Tanana Commercial Company LLC. Final 2024 Site Characterization Report for the Napaskiak Former BIA School Day Tanks, Napaskiak, Alaska. April 2025.

TCC conducted a site characterization at the site in July 2024 which included advancing and sampling soil from ten test pits, and installation and sampling of five monitoring wells. In October 2024, TCC conducted a second round of groundwater sampling of the site’s wells. The 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. Petroleum contamination remains at the project site with the highest concentrations in the vicinity of the former header. Lower-level contamination was also encountered at other areas of the site that may warrant additional investigation on the extent.

Concentrations were less than cleanup levels in the July 2024 samples, with the exception of Well MW4. Product was visible in the July 2024 purgewater from Well MW4 so the well was not sampled; product was not visible in the October 2024 purgewater from Well MW4. The October 2024 groundwater samples from Wells MW1, MW3, and MW4 also contained DRO exceedances.

In addition, Well MW3 contained naphthalene, 1-methylnaphthalene, 1,2,4-trimethylbenzene, and 1,3,5-trimethylbenzene exceedances; and Well MW2 contained a naphthalene exceedance. Further investigation of the extent of contamination in the soil and additional groundwater monitoring was recommended.

2.0 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 that have historically exceeded cleanup levels:

• DRO (soil and groundwater)

• 1-Methylnapthalene (soil and groundwater)

• 2-Methylnapthalene (soil only)

• Naphthalene (soil and groundwater)

• 1,2,4-Trimethylbenzene (soil and groundwater)

• 1,3,5-Trimethylbenzene (soil and groundwater)

• Benzene (soil only)

• Ethylbenzene (soil only)

• Xylenes (soil only)

February 2026 6

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)

3.0 SAMPLING METHODOLOGY

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

3.1 Soil Sampling Methods

Soil samples were collected 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.

Field screening samples were collected during the field activities. The field headspace readings from the test pit sampling activities were collected by filling re-sealable quart size bags approximately 1/3 to 1/2 full with soil. The bags were then agitated before being allowed to develop for at least 10 minutes, but no longer than an hour. During this time the soils were warmed to a minimum temperature of 40°F. After the samples were warmed and allowed to develop, the probe of the photoionization detector (PID) was inserted into the bag about one-half of the headspace depth and the highest displayed reading were recorded in the field notes along with other pertinent information such as time of collection and reading, the soil characteristics, depth at which the sample was collected, and the field personnel.

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.

3.2 Groundwater Sampling Methods

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.

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The monitoring wells were purged using low-flow sampling methods per the Environmental Protection Agency’s 2019 Low Stress (low flow) Purging and Sampling Procedure for the Collection of Groundwater Samples from Monitoring Wells and the ADEC’s 2013 Monitoring Well Guidance. The wells were sampled in the order from least to most contaminated.

A decontaminated positive displacement submersible mini-monsoon pump and disposable tubing were initially used to purge and collect the groundwater monitoring well samples and the sample parameters were allowed to stabilize prior to sampling. Since wells purged dry and there were pump mechanical issues, a disposable bailer was used on select wells once wells recovered to 80% pre-purge volume. When samples were being collected, the pump was initially placed to be within 1 foot of the water surface or the bailer was slowly placed into the well casing. Samples were collected by removing the inflow hose from the flow-through cell into the laboratory-provided sample containers directly from the tube or bailer; 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 B.

4.0 FIELD ACTIVITIES

The 2025 field activities were conducted between August 11 and 13, 2025. The field activities included a site characterization to further delineate the lateral and vertical extent of contamination.

This included collection of groundwater samples from the site’s five wells as well as advancing eight new test pits. Field notes of the field activities are provided in Appendix B. Photographs of the field activities are provided in Appendix C.

Connor McCarron and Lexis Goffena were the Qualified Environmental Professionals (QEPs) collecting the samples and directing the field work. The level loop survey was conducted by Dale Erickson of TCC.

4.1 Work Plan Variances

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

• 2-inch disposable bailers were used for the sampling of Wells MW2 and MW3 instead of a peristaltic pump/mini-monsoon pump due to lack of water, purging dry, and mechanical issues with the pump.

• While not being included in the 2025 scope, a new level loop survey was completed due to frost jacking of monitoring wells installed in 2024.

• PAH analyses were unable to be collected from Well MW2 due to low recovery.

• Well MW1 had frost jacked and the well appeared to have been compromised. A sample was not collected.

• No duplicate samples were collected due to low recovery.

February 2026 8

4.2 Site Characterization Activities

The site characterization activities included advancing test pits and sampling monitoring wells as well as completing a new level loop survey.

4.2.1 Test Pits

A total of eight test pits were advanced on August 12 and 13, 2025. 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 was 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:

• Extent of contamination in the vicinity of Test Pit TP2: Test Pits TP12 and TP13

• Extent of contamination in the vicinity of Test Pit TP5: Test Pits TP14 through TP16

• Extent of contamination to the south, west, and east of the former header release: Test Pits

TP17 through TP19

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. None were identified.

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 between 2 and 8 ft bgs.

Table 1 – GPS Coordinates of Sample Locations

Well ID Latitude Longitude

MW1 60.7077418 -161.7630315

MW2 60.7076141 -161.7639312

MW3 60.7080600 -161.7637957

MW4 60.7084485 -161.7633505

MW5 60.7079984 -161.7617360

TP12 60.707583 -161.763761

TP13 60.707845 -161.764008

TP14 60.707837 -161.761801

TP15 60.708181 -161.761107

TP16 60.708409 -161.761587

TP17 60.708544 -161.762858

TP18 60.708529 -161.763422

TP19 60.708414 -161.763716

4.2.2 Monitoring Well Maintenance and Sampling

Samples were attempted to be collected from each of the site’s five wells, as shown on Figure 5.

Each well was sampled using the methods described in Section 4.2. Water level measurements

February 2026 9 were conducted prior to purging/sampling between August 11 and 13, 2025. Note, several of the wells appeared to have jacked up or sank since the October 2024 event, likely due to the high-water table across the site. Wells that had jacked up out of the ground (Wells MW1 and MW2) were cut down and repaired. The 5-foot well screens for these remain within beneath the water table.

Wells MW2 and MW3 samples were collected over the three field days due to purging dry, the field team was only able to get a partial sample from Well MW2. Monitoring Well MW1 was clogging the pump and determined too turbid to sample and due to time constraints was not able to be cleaned up. Monitoring Well MW5 had plenty of water and a full sample was taken.

Trace product (<0.01 ft) was encountered in Well MW4 and therefore was not sampled.

Purgewater from Well MW4 had a distinct smell and slight sheen/foamy purge water. A product recovery sock was deployed in the well and will be left until the next monitoring event.

4.2.3 Water Level Measurements and Flow Direction

Water level measurements were collected for the site’s wells on August 11, 2024, prior to well purging and sampling. The water level measurements are provided in Table 2.

Table 2 – August 2025 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 5.15 6.91 3.02 0.20 3.22 3.89

MW2 5.38 7.85 4.15 0.20 4.35 3.7

MW3 7.50 9.56 6.09 0.20 6.29 3.47

MW4 6.50 9.09 5.47 0.20 5.67 3.62

MW5 5.17 8.63 1.48 0.10 1.58 7.15

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 groundwater at the site prior to well development appears to flow to the west.

4.3 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

February 2026 10 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, inspected for sheen, and discharged onto the ground surface next to the respective sample location.

5.0 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.

5.1 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 Pit TP16 around 3 to 4 feet bgs, noting this test pit was located just north of the existing school building. Water was encountered between 2 and 8 feet bgs.

Field observations included the presence of organics and some debris but minimal petroleum odors were encountered. Organics were encountered in all test pits with Test Pits TP13, TP17, and TP19 having organics at deeper intervals. Debris (i.e., trash and scrap metal) was encountered at Test Pits TP13 and TP18.

5.2 Test Pit Soil Results

Samples were collected and submitted for analysis from each test pit. Detectable concentrations of DRO were reported in each test pit soil sample. Detectable levels of acetone were also reported in the samples from Test Pits TP14, TP17, and TP18. Both analytes were reported at concentrations below cleanup levels. The remaining analytes were not detected. Detectable analytical results are listed below in Table 4.

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Table 3 – Detected 2025 Soil Analytical Results

Analyte Analysis Unit Cleanup Level* TP12-5.5 TP13-5.5 TP14-5.9 TP14-15.9~ TP15-7.8 TP16-6.0 TP17-6.0 TP18-3.0 TP18-13.0~ TP19-7.5 STB

Sample Depth - ft - 5.5 5.5 5.9 5.9 7.8 6.0 6.0 3.0 3.0 7.5 -

Field Headspace MiniRae 3000 PID ppm - 0.0 0.0 0.0 0.0 3.2 2.7 7.0 3.8 3.8 5.7 -

Diesel Range Organics AK102 mg/kg 250 16.1 J 16.1 J 37.6 26.7 J 22.6 J 19.3 J 17.9 J 22.1 J 22.8 J 14.0 J -

Volatile Organic Compounds (VOC)

1,1,1,2-Tetrachloroethane SW8260D ug/kg 22 22.0 U 20.6 U 29.5 U 31.7 U 21.7 U 22.7 U 26.5 U 21.4 U 22.7 U 19.4 U 15.0 U

1,1,2,2-Tetrachloroethane SW8260D ug/kg 3 2.20 U 2.06 U 2.95 U 3.17 U 2.17 U 2.27 U 2.66 U 2.14 U 2.27 U 1.94 U 1.50 U

1,1,2-Trichloroethane SW8260D ug/kg 1.4 1.10 U 1.03 U 1.47 U 1.58 U 1.08 U 1.14 U 1.33 U 1.07 U 1.13 U 0.968 U 0.748 U

1,2,3-Trichloropropane SW8260D ug/kg 0.031 2.20 U 2.06 U 2.95 U 3.17 U 2.17 U 2.27 U 2.66 U 2.14 U 2.27 U 1.94 U 1.50 U

1,2-Dibromoethane SW8260D ug/kg 0.24 1.65 U 1.54 U 2.21 U 2.38 U 1.62 U 1.70 U 2.00 U 1.61 U 1.70 U 1.46 U 1.13 U

1,4-Dichlorobenzene SW8260D ug/kg 37 27.5 U 25.8 U 36.8 U 39.7 U 27.1 U 28.4 U 33.2 U 26.7 U 28.3 U 24.3 U 18.7 U

2-Hexanone SW8260D ug/kg 110 132 U 124 U 177 U 191 U 130 U 137 U 160 U 128 U 137 U 116 U 90.0 U

Acetone SW8260D ug/kg 38000 275 U 258 U 379 J 347 J 271 U 284 U 202 J 163 J 213 J 243 U 187 U

Bromomethane SW8260D ug/kg 24 22.0 U 20.6 U 29.5 U 31.7 U 21.7 U 22.7 U 26.5 U 21.4 U 22.7 U 19.4 U 15.0 U

Chloroform SW8260D ug/kg 7.1 6.60 U 6.20 U 8.85 U 9.52 U 6.50 U 6.82 U 7.95 U 6.41 U 6.81 U 5.83 U 4.49 U cis-1,3-Dichloropropene SW8260D ug/kg 18 13.7 U 12.9 U 18.4 U 19.8 U 13.5 U 14.2 U 16.6 U 13.4 U 14.2 U 12.1 U 9.38 U

Dibromochloromethane SW8260D ug/kg 2.7 5.50 U 5.16 U 7.37 U 7.95 U 5.42 U 5.69 U 6.64 U 5.35 U 5.67 U 4.85 U 3.74 U

Dibromomethane SW8260D ug/kg 25 27.5 U 25.8 U 36.8 U 39.7 U 27.1 U 28.4 U 33.2 U 26.7 U 28.3 U 24.3 U 18.7 U

Hexachlorobutadiene SW8260D ug/kg 20 22.0 U 20.6 U 29.5 U 31.7 U 21.7 U 22.7 U 26.5 U 21.4 U 22.7 U 19.4 U 15.0 U

Naphthalene SW8260D ug/kg 38 27.5 U 25.8 U 36.8 U 39.7 U 27.1 U 28.4 U 33.2 U 26.7 U 28.3 U 24.3 U 18.7 U trans-1,3-Dichloropropene SW8260D ug/kg 18 13.7 U 12.9 U 18.4 U 19.8 U 13.5 U 14.2 U 16.6 U 13.4 U 14.2 U 12.1 U 9.38 U

Trichloroethene SW8260D ug/kg 11 11.0 U 10.4 U 14.7 U 15.8 U 10.8 U 11.4 U 13.3 U 10.7 U 11.3 U 9.68 U 7.49 U

Vinyl chloride SW8260D ug/kg 0.8 0.877 U 0.825 U 1.18 U 1.27 U 0.862 U 0.907 U 1.06 U 0.855 U 0.907 U 0.780 U 0.599 U

Other VOCs SW8260D ug/kg varies ND ND ND ND ND ND ND ND ND ND ND

Polyaromatic Hydrocarbons (PAH) 8270E SIM ug/kg varies ND ND ND ND ND ND ND ND ND ND - Notes on the following page

February 2026 12

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

37.6 Analyte detected below MTG Cleanup Level

J Analyte was detected at an estimated concentration, less than the cleanup level.

22.0 U Analyte non-detect

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

ND Non-detect

- Not sampled or not applicable

5.3 Groundwater Monitoring Results

Detectable concentrations of DRO and toluene were reported in the three wells sampled in 2025.

In addition, benzene, dichlorodifluoromethane, naphthalene, and phenanthrene were also detected in one or more wells. None of the detectable concentrations exceeded cleanup levels.

The detectable analytical results are listed in Table 5.

Table 4 – Detected 2025 Water Analytical Results

Analyte Analysis Unit Cleanup Level* MW2-5.6 MW3-7.0 MW5-4.7 GWTB

Depth to Groundwater - ft btoc - 5.6 7.0 4.7 - Diesel Range Organics AK102 mg/L 1.5 0.781 J 0.929 J 0.848 J - DRO Silica Gel AK102 mg/L 1.5 0.960 U 0.998 U 0.892 U Polyaromatic Hydrocarbons (PAHs)

Naphthalene 8270E SIM LV ug/L 1.7 ** 0.0833 UJ- 0.0482 J- - Phenanthrene 8270E SIM LV ug/L 170 ** 0.0350 J- 0.0733 UJ- - Other PAHs 8270E SIM LV ug/L varies ** ND ND -

Volatile Organic Compounds (VOC's) 1,2,3-Trichloropropane SW8260D ug/L 0.0075 0.750 U 0.750 U 0.750 U 0.750 U Benzene SW8260D ug/L 4.6 0.140 J 0.300 U 0.300 U 0.300 U Dichlorodifluoromethane SW8260D ug/L 200 0.750 U 0.750 U 8.28 0.750 U Toluene SW8260D ug/L 1100 0.370 J 16.7 59.2 0.750 U Other VOCs SW8260D ug/L varies ND ND ND ND

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

16.7 Analyte detected below Table C Cleanup Level

J Analyte was detected at an estimated concentration, less than the cleanup level.

0.750 U Detection limit greater than the Cleanup Level

February 2026 13

6.0 QUALITY CONTROL REVIEW

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

6.1 SGS Report 1254388 Soil Samples

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

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

6.2 SGS Report 1254357 Groundwater Samples

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

• The PAH samples were received outside of hold time. As a result, the PAH sample results may be biased low. The affected samples are flagged with a J- on Table 5.

• 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 August 2025.

• A duplicate sample was not able to be collected due to the low recovery in the monitoring wells.

7.0 DISCUSSION

A discussion of the results from the 2025 sample results are described in further detail below.

7.1 Soil Sampling Discussion

Soil samples were collected from the test pits advanced across the site. Test pit samples focused on identifying the lateral and vertical extents of contamination around the header release and in the area of Test Pits TP2 and TP5. Based on the results from the 2025 activities, the extent of contamination near the header release appears to be defined and does not appear to have migrated offsite, including downgradient to the Napaskiak Slough.

Test pits were advanced in the southwest portion of the site, near the 2024 Test Pit TP2. Due to the location of offsite infrastructure and presence of contamination along the property boundary, test pits were unable to be placed directly downgradient of former Test Pit TP2. However, Test

February 2026 14

Pits TP12 and TP13, placed to the northwest and southeast, did not contain concentrations greater than the cleanup levels.

Test Pits TP14, TP15, and TP16 were advanced to the north, east, and south of former Test Pit TP5. The 2025 test pits did not contain contaminant concentrations greater than cleanup levels.The extent of contamination associated with Test Pit TP5 appears to be defined.

7.2 Groundwater Monitoring Discussion

Groundwater samples were collected from three of the site’s five wells. Well MW1 did not contain adequate water to be able to be sampled and Well MW4 contained product. Well MW4 has historically contained high concentrations or trace product.

Wells MW2, MW3, and MW5 did not contain concentrations greater than cleanup levels.

Previously exceedances were reported for naphthalene (MW2 in July and October) and DRO (MW3 in October) in two of these three wells.

7.3 Conceptual Site Model Discussion

A conceptual site model (CSM) was updated for the site with a focus on the identifying exposure pathways that may need further investigation per the ADEC’s January 2017 Guidance on Developing Conceptual Site Models. The Human Health Conceptual Site Model Graphic Form and Human Health Conceptual Site Model Scoping Form and Standardized Graphic are included in Appendix E.

The primary source of contamination at the site are leaks and spills from ASTs and pipelines. The July 2024 investigation identified DRO, benzene, ethylbenzene, xylenes, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, 1-methylnaphthalene, 2-methylnaphthalene, and naphthalene being present at the site in the soil between 0 and 7 feet bgs. DRO, 1-methylnaphthalene, naphthalene, 1,2,4-trimethylbenzene, and 1,3,5-trimethylbenzene were also reported in the groundwater at concentrations greater than cleanup levels in the October 2024 sampling event. Several of these contaminants are known to permeate the skin and are volatile. Due to the presence of volatile compounds in the soil and in the groundwater at the site, air is also potentially impacted media.

The pathways identified as complete in the CSM include: ingestion of groundwater, incidental soil ingestion, dermal absorption of contaminants from soil, and inhalation of outdoor air. Inhalation of indoor air is considered incomplete due to site structures being placed on piles. Further, much of the site that is contaminated is vegetated so inhalation of fugitive dust and direct contact with sediment is not considered potentially complete or warranting further investigation

In 2025, ingestion of surface water and dermal exposure to contaminants in groundwater and surface water were evaluated. Based on the 2025 sample results, the contamination does not appear to have migrated to the Napaskiak Slough. As a result, this pathway is considered incomplete.

The site is in a residential area and near the current school. As a result, the current and future receptors will include residents, commercial or industrial workers, site visitors, trespassers, subsistence users, and construction workers.

February 2026 15

8.0 INVESTIGATIVE DERIVED WASTE MANAGEMENT

Investigation derived waste included soil, purge/decontamination water, sampling disposables, and personal protective equipment (PPE).

• Purge/decontamination water was treated using a GAC filter and discharged onsite. An estimated 10 gallons of purgewater was processed through the GAC during the August monitoring event.

• Soil generated during test pits and monitoring well installation activities were used to backfill the respective test pits upon completion of the sampling activities.

• Investigation derived waste (IDW) comprised of gloves, spoons, bailers, tubing from the groundwater monitoring, PVC cutoffs, and other sampling disposables were disposed of at Napaskiak Landfill.

9.0 CONCLUSIONS AND RECOMMENDATIONS

Petroleum contamination remains at the project site with the highest concentrations in the vicinity of the former header with other areas having concentrations greater than cleanup levels. The extent of soil contamination appears mostly defined based on the 2025 results, although additional investigation may still be warranted in select areas as identified below. In 2025, this is the third sampling event of the site’s monitoring wells. Product continues to be detected in one well, however the remaining viable wells did not contain concentrations above cleanup levels.

Based on the results of the 2025 field activities, we recommend the following to advance the site towards closure:

• Continued water monitoring to determine if the concentrations are stable or decreasing in the site’s wells. This request will need to be made in the work plan for future site groundwater monitoring activities.

• Assess the extent of contamination between Test Pits TP12 and TP13, and between Test Pits TP14 and TP15.

• Be prepared to cut off well casings and resurvey monitoring wells that may have jacked from the shallow water table and freeze-thaw cycles.

• Replace the product recovery sock and continue product recovery.

• Assess Well MW1 for further frost jacking and/or viability.

• Evaluate cleanup methods for the site in consideration of the potential impacts to the permafrost at the site and limited resources in the community (e.g., landfarm, dig and haul, in-situ treatments, limited removal action of hot spots, product recovery/long term monitoring).

February 2026 16

10.0 REFERENCES

ADEC. 2013. Monitoring Well Guidance. September.

ADEC. Oil and Other Hazardous Substances Pollution Control, 18 AAC 75. 18 October 2023.

ADEC. Field Sampling Guidance. August 2024.

Environmental Protection Agency. Low Stress (low flow) Purging and Sampling Procedure for the Collection of Groundwater Samples from Monitoring Wells. 19 September 2017.

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

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

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

Tanana Commercial Company LLC. Final 2024 Site Characterization Report for the Napaskiak Former BIA School Day Tanks, Napaskiak, Alaska. April 2025.

APPENDIX A

Figures

VICINITY MAP

BETHEL C-8 TOPO (1954)

NAPASKIAK FORMER BIA

SCHOOL DAY TANKS

NAPASKIAK, ALASKA 1

FIGURE

TANANA COMMERCIAL

COMPANY

DATE:

10/8/2025

PROJECT SITE

NAPASKIAK VILLAGE

LAGOON

NGRAPHIC SCALE (IN FEET)

0 500 1000 2000 40001000

PROJECT AREA

NAPASKIAK FORMER BIA

SCHOOL DAY TANKS

NAPASKIAK, ALASKA 2

FIGURE

TANANA COMMERCIAL

COMPANY

DATE:

10/8/2025

Z. JOHN WILLIAMS

SCHOOL (DEMOLISHED)

LANDFILL

FORMER BIA ABANDONED SEWAGE LAGOON

FORMER SCHOOL WELL HOUSE

FORMER SCHOOL TANK FARM

HEADER RELEASE

NAPASKIAK VILLAGE

LAGOON

PK09/PK15 HOUSING

PK08 ABANDONED BUILDING

(DEMOLISHED)

PK06 BUILDING (DEMOLISHED)

PK07 UTILITY BUILDING (DEMOLISHED)

CURRENT Z. JOHN

WILLIAMS SCHOOL

NAPASKIAK SLOUGH

WATER

TREATMENT

PLANT

N

JULY 2021 GOOGLE EARTH PRO IMAGERY

GRAPHIC SCALE (IN FEET)

0 50 100 200

NAPASKIAK

SCHOOL SITE

BIA SCHOOL

LOT - TRACT B BIA SCHOOL

LOT - TRACT A

HISTORIC SAMPLE LOCATIONS

NAPASKIAK FORMER BIA

SCHOOL DAY TANKS

NAPASKIAK, ALASKA 3

FIGURE

TANANA COMMERCIAL

COMPANY

DATE:

12/19/2025

HEADER RELEASE

NAPASKIAK SLOUGH

AREA C: TANK

FARM PIPING

RELEASE

N

JULY 2021 GOOGLE EARTH PRO IMAGERY

AREA D: TANK FARM

AREA B: PIPING LEAK

AREA A: AST DAY TANKS

FORMER BIA ABANDONED

SEWAGE LAGOON

WELL HOUSE

LEGEND

Approximate location of former well point location (Oasis 2011)

Approximate location of former test pit location (Oasis 2011)

AREA WITH BURIED

EMPTY 55-GALLON

DRUMS

Approximate location of insitu landfarm cell (ERM 2013)

Approximate location of trench sample location (ERM 2013) Approximate location of sewage lagoon sample (Oasis 2011)

RED Symbols denote previous; DRO greater than CUL

GRAPHIC SCALE (IN FEET)

0 25 50 100

Approximate location of former test pit location (TCC 2024)

2025 SOIL SAMPLE

LOCATIONS

NAPASKIAK FORMER BIA

SCHOOL DAY TANKS

NAPASKIAK, ALASKA 4

FIGURE

TANANA COMMERCIAL

COMPANY

DATE:

2/7/2026

HEADER RELEASE

NAPASKIAK SLOUGH

AREA C: TANK

FARM PIPING

RELEASE

N

JULY 2021 GOOGLE EARTH PRO IMAGERY

AREA D: TANK FARM

AREA B: PIPING LEAK

AREA A: AST DAY TANKS

FORMER BIA ABANDONED

SEWAGE LAGOON

LEGEND

Approximate location of former test pit location containing concentrations above cleanup levels (Oasis 2011)

AREA WITH BURIED

EMPTY 55-GALLON

DRUMS

Approximate location of insitu landfarm cell (ERM 2013)

Approximate location of trench sample location containing concentrations above cleanup levels (ERM 2013) Test Pit advanced and completed as a monitoring well in July 2024

Test Pit advanced August 2025

Approximate location of former well point location containing concentrations above cleanup levels (Oasis 2011)

GRAPHIC SCALE (IN FEET)

0 25 50 100

BLACK symbology indicates August 2025 sample results were less than cleanup levels

GRAY symbology indicates historic sample location

TP12

TP13

TP19

TP18

TP17

TP16

TP15

TP14

TP2

TP1

TP3

TP4

TP11 TP9

TP5

TP6

TP10

TP7

Test Pit advanced in July 2024

3.

4.

4.5

5.

5.5

6.5

2025 MONITORING

WELL SAMPLES

NAPASKIAK FORMER BIA

SCHOOL DAY TANKS

NAPASKIAK, ALASKA 5

FIGURE

TANANA COMMERCIAL

COMPANY

DATE:

12/19/2025

HEADER RELEASE

NAPASKIAK SLOUGH

AREA C: TANK

FARM PIPING

RELEASE

N

JULY 2021 GOOGLE EARTH PRO IMAGERY

AREA D: TANK FARM

AREA B: PIPING LEAK

AREA A: AST DAY TANKS

FORMER BIA ABANDONED

SEWAGE LAGOON

WELL HOUSE

LEGEND

AREA WITH BURIED

EMPTY 55-GALLON

DRUMS

Approximate location of insitu landfarm cell

(ERM 2013)

MW5

MW4

MW3

MW2

MW1

Product Detected

Approximate location of monitoring well containing product during the 2025 sampling event

Approximate location of monitoring well containing concentrations less than cleanup levels during the 2025 sampling event

Groundwater Elevation Contour based on August 11, 2025 groundwater measurements and level loop survey conducted on August 12, GRAPHIC SCALE (IN FEET)

0 25 50 100

Unable to be sampled due to limited water and high turbidity.

4.3 Decontamination Procedures

Chain of Custody / Sample Receipt Forms