2025_Eek_Report_0001.pdf

FINAL

2025 Site Characterization Report

For the Eek Former BIA School Tanks

Eek, Alaska

ADEC File. No. 2412.38.004 ADEC Hazard ID. 25493

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

May 2026

Former BIA School Site, looking east from the west property boundary

FINAL

Site Characterization Report

Eek Old BIA School and Tanks

ADEC File No. 2412.38.004

ADEC Hazard ID 25493

Prepared by:

Tanana Commercial Company LLC PO Box 77069 Tanana, Alaska 99777

Written by:

Shayla Marshall, QEP Project Manager

Site Characterization Report – FINAL Eek Old BIA School and Tanks; ADEC File No. 2412.38.004 May 2026 i

TABLE OF CONTENTS

1.0 SITE DESCRIPTION AND BACKGROUND

1.1 Project Purpose and Objectives

1.2 Site Location

1.3 Background

1.4 Property Records

2.0 CONTAMINANTS OF CONCERN AND APPLICATION

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 Water Level Measurements

4.3 Decontamination Procedures

5.0 SAMPLING RESULTS

5.1 Subsurface Conditions

5.2 Test Pit Soil Results

6.0 QUALITY CONTROL REVIEW

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

May 2026 ii

TABLES

Table 1 – Water Level Measurements Table 2 – Detected Soil Analytical Results

FIGURES

Figure 1 – Vicinity Map Figure 2 – Historical Sample Locations Figure 3 – 2024 Monitoring Well Sample Locations Figure 4 – 2025 Soil Sample Locations Figure 5 – 2025 Monitoring Well Locations

APPENDICES

Appendix A – Figures Appendix B – Limited Liability Report Appendix C – Field Notes Appendix D – Photo Pages Appendix E – SGS Laboratory Report and Laboratory Data Review Checklist Appendix F – Human Health Conceptual Site Model Graphic Form and Human Health

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

May 2026 iii

ACRONYMS AND ABBREVIATIONS

AAC Alaska Administrative Code ADEC Alaska Department of Environmental Conservation AK Alaska AST Aboveground Storage Tanks bgs Below Ground Surface BIA Bureau of Indian Affairs BTOC Below Top of Casing COPC Compounds of Potential Concern CSM Conceptual Site Model DRO Diesel Range Organics DQO Data Quality Objectives Ft Feet GAC Granulated Activated Carbon GRO Gasoline Range Organics IDW Investigation Derived Waste LKSD Lower Kuskokwim School District LOD Limits of Detection mg/kg Milligrams Per Kilogram mL Milliliters MAC Maximum Allowable Concentration MTG Migration to Groundwater PACP Property Assessment and Cleanup Plan PAH Polyaromatic hydrocarbon PID Photoionization Detector PPE Personal Protective Equipment QC Quality Control QEP Qualified Environmental Professional RPD Relative Percent Difference RRO Residual Range Organics SGS SGS North America TCC Tanana Commercial Company LLC TPECI Travis/Peterson Environmental Consulting, Inc.

VOC Volatile Organic Compound

May 2026 1

FINAL

Site Characterization Report

Eek Old BIA School and Tanks

ADEC File No. 2412.38.004

ADEC Hazard ID 25493

This report outlines the 2025 site characterization activities at the Old Bureau of Indian Affairs (BIA) School and Tanks in Eek, Alaska. The site is identified as Alaska Department of Environmental Conservation (ADEC) Contaminated Sites File No. 2412.38.004, Hazard ID 25493.

Work is in accordance with the April 10, 2025 Contract No. 140A0525P0012 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 further site characterization to delineate the lateral and vertical extent of contamination in areas needing further investigation based on the 2024 sample results; and

• Conduct groundwater monitoring of five wells to determine groundwater conditions.

1.2 Site Location

The village of Eek is located on the south bank of the Eek River, approximately 35 miles south of Bethel, Alaska. The site is located in the northeast ¼ of the southwest ¼ of Section 31, Township 2 North, Range 73 West, Seward Meridian, Alaska (Baird Inlet A-1 USGS Quadrangle). The Vicinity Map is included as Figure 1 (Appendix A). The legal address of the former BIA property is Lots 1, 2, and 3, US Survey 2021. The property boundaries are shown on Figure 2 in Appendix A.

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 2 (Appendix A).

May 2026 2

SLR. Final Property Assessment and Cleanup Plan, Old BIA School Property, Eek, Alaska.

February 2011.

A Property Assessment and Cleanup Plan (PACP) was prepared for the old BIA school property site for the purpose of the PACP was to provide information to the community for the purpose of acquiring funding for the cleanup and reuse of the property.

The Old BIA School Tank Farm contained five 10,000-gallon vertical tanks. Aerial photographs suggest that barrels were used for fuel storage in 1964 but replaced with aboveground storage tanks (ASTs) in the 1983 aerial photographs. Interviews with people familiar with the site indicated that three older ASTs were drained around 2005 where fuel was removed from the lines and tanks, and the piping and associated day tanks were disconnected. Some pipelines were moved and stockpiled near the pump house/generator building while others remained at the original location. The remaining two ASTs are filled by barge once a year in the summer via rubber hoses and a marine header. The fuel is accessed via an aboveground fill valve near the teachers’ housing building. An estimated 1,000 gallons of fuel are transported to the new school each winter via 55-gallon barrels, a pump, and fittings.

There were previously three day tanks.

• Day Tank 1 (500 gallons) was located immediately east of the teachers’ housing building, just south of the current fill value. Reportedly it was removed in 1993 and relocated to the new school where at the time, it was currently being used.

• Day Tank 2 (500 gallons) was located on a tank stand immediately west of the red building near the electrical panel and meter. The tank and piping connecting it to the pump house were removed around 2005.

• Day Tank 3 (100 to 200 gallons) was a series of stacked fuel storage containers. It was located near the shop. The date of the removal was not noted in the PACP.

At the time of the PACP, three tanks in the Old BIA School Tank Farm were used for fuel storage by the Lower Kuskokwim School District (LKSD) and the pipelines were disconnected. Three of the tanks were listing toward the south. Water present at the site exhibited hydrocarbon sheen in some locations and strong hydrocarbon odors, surface staining, and stressed vegetation were also noted. These locations included the area near the AST fill valve, within and around the containment area, former day tank locations, and areas where pipeline previously entered the buildings.

The Old BIA School buildings are no longer accessible or used, with the exception of the red building that is used for storage. The red building was reportedly built in 1970s which the other buildings were built in the 1950s. The Old BIA School building was used until 1980 or 1981. The red school building (labeled as the New School on Figure 2) was used as a high school until 1988 or 1989, when the new school was built. After that, the building was used as a preschool and teacher housing until approximately 2005 after which the fuel pipelines were disconnected. The teacher housing was used until about 1994 or 1995; it was boarded up thereafter.

May 2026 3

SLR assessed the subsurface conditions in September 2010. A total of 44 field screening and 10 analytical samples, including two duplicates, were collected from 1 or 2 feet below ground surface (bgs). Test holes were advanced in the immediate vicinity of the tank farm, other onsite ASTs, pipelines, and other features that may have been impacted. Step out holes were advanced based on field indicators such as elevated field screening results, visual observations, and/or olfactory evidence. Water was encountered at 2 feet bgs and subsurface soil was primarily peat although silt or sand was present within the peat at several locations. Permafrost was identified at 2 feet bgs in July 2010 by Travis/Peterson Environmental Consulting, Inc.

Samples FS8, FS9, FS18 through FS23, FS30, FS32, FS34 through FS36, and SS02 through SS08 indicated fuel contamination. These locations are depicted as red symbols on Figure 2. The majority of the impact was noted on the west side of the site near the pump house and an AST.

Diesel range organics (DRO) was the only analyte detected at a concentration above ADEC Method Two cleanup levels with a maximum level of 46,600 milligrams per kilogram (mg/kg) reported. Gasoline range organics (GRO), toluene, ethylbenzene, xylenes, and 14 polyaromatic hydrocarbons (PAHs) were also detected but below cleanup levels.

SLR also reviewed spill reports for the Eek High School. In May 14, 1997 25 gallons of heating oil was spilled from a day tank; 80 percent of the free product was recovered. SLR suggested that this was located at the site and may be the source of the impacted soil at the western portion of the site. The second spill was on March 12, 2005 when 200 to 300 gallons of heating oil was released when a fuel line between a fuel tank and day tank broke. There were no cleanup activities noted and the exact location was not determined based on the spill report.

There is one registered drinking water system that utilizes surface water as the source (AK2270281). The well log for the Old BIA School Property noted that there is frozen intermittent layers of sand and silt to approximately 235 feet at which thawed soils were first encountered. Two zones of salt water seepage were identified at approximately 110 to 120 feet and 145 to 150 feet bgs. A second well log shows frozen blue clay between 59 to 232 feet bgs; the top 59 feet was not logged. A pea gravel aquifer was located between 232 and 245 feet bgs. Salt water seepage was noted at 110 feet bgs and the static water level was 23.25 feet.

The PACP recommended the solid waste be removed, asbestos abatement and sampling be performed, the buildings be demolished, and excavation of the contaminated soil to a depth of 2 feet be conducted. Specific to remediation strategies, the four areas of impact with an estimated 535 cubic yards include:

• Old BIA Tank Farm: Estimated volume 300 cubic yards.

• Pump House Area: Approximately 1,500 square feet and 115 cubic yards. Total depth estimated between 0 to 2 feet bgs.

• AST Area: Approximately 1,200 square feet and 90 cubic yards. Total depth estimated between 0 to 2 feet bgs.

May 2026 4

• Hot Spots: three areas with two approximately 100 square feet and one approximately 200 square feet. Total estimated depth is 2 feet for a total of 30 cubic yards of impacted soil between the three areas.

Passive biopile construction, road base encapsulation, daily landfill cover, landfarming, and offsite shipment for treatment or disposal were identified as potential alternative soil management strategies.

Travis/Peterson Environmental Consulting, Inc. Eek Tank Farms. 30 August 2010.

In July 2010 Travis/Peterson Environmental Consulting, Inc. (TPECI) inspected the Old BIA Tank Farm and collected eight analytical samples from 0 to 2 feet bgs. A permafrost layer was encountered at approximately 2 feet bgs. DRO and residual range organics (RRO) was detected at levels up to 31,100 mg/kg and 16,000 mg/kg, respectively. GRO, ethylbenzene, and xylenes were also detected but at concentrations below cleanup levels. TPECI estimated 300 cubic yards of contaminated soil to be present at the Old BIA Tank Farm.

Tanana Commercial Company LLC. 2024 Site Characterization Report for the Eek Old BIA School and Tanks. April 2025.

In July 2024 TCC advanced shallow test pits and installed and sampled nine monitoring wells across the site. The areas investigated included the Old BIA Tank Farm, Pump House Area, and AST area.

At the time of the site visit, no structures were present. According to Terry Petluska, a representative of the Eek Tribal Council, the buildings were removed over a year ago by UIC. The demolition occurred in the winter when the ground was frozen to minimize impact as the area is very wet. He understands that UIC burned the wastes after the asbestos was removed. Those wastes were then placed in a landfill UIC built specifically for the project. He believed the landfill was located next to the current school but was not sure of the exact location. The footprints of the former structures were visible as there was some debris left behind; however fill is not readily available in the community so no backfill was used. Each of the former buildings were ‘built up’ so that they were higher than the surrounding property due to the high-water table.

Petroleum contamination was present at various locations across the site. Several soil samples also contained concentrations at levels greater than the ADEC maximum allowable concentration (MAC) cleanup level for DRO and RRO in soil. The contamination appears to be most impacted in the vicinity of the Former “New” BIA School and adjacent to the Former BIA Tank Farm, although the extent of contamination and whether it extends off property is not known. The contamination appears shallow (within the top 2 feet) and a shallow water table was present at the time of the field activities. Although permafrost was not encountered during the July 2024 field activities, it has been encountered within the top 2 feet during previous investigations.

Contamination was also encountered in the site’s shallow monitoring wells during the July 2024 field activities. The small water column due to the perched water and combined with silty soil has

May 2026 5 likely contributed to the low water recovery in the site’s monitoring wells and may help minimize the migration of contaminated water across the site. Further, one of the wells did contain concentrations that exceeded cleanup levels, but soil samples and field indications (odor, sheen) suggested that the concentrations may be biogenic in nature. Additional investigation was recommended to determine if contamination extends off property and/or is comingled, determine vertical extent of contamination, collect additional groundwater samples, and determine the depth of permafrost. The 2024 sample locations are included as Figures 2 and 3.

1.4 Property Records

A Limited Liability Report was received by First American Title. The following documents were obtained for Lot 3, U.S. Survey No. 2021, Bethel Recording District and copies of the documents referenced above are provided in Appendix B.

• Quitclaim Deed recorded March 16, 1989: The BIA granted the property known as the former Eek School Reserve to the State of Alaska Department of Education.

• U.S. Survey No. 2021 recorded April 23, 1993: The property was surveyed in August 1991.

At the time of the survey, there was a fenced tank farm with five tanks, two houses, a frame building, three sheds, a wood platform and a pumphouse. The size of Lot 3 is 3.06 acres.

According to the BIA, Lots 1 and 2 were conveyed to the Village of Eek. Documents for these lots were not provided by First American Title.

2.0 CONTAMINANTS OF CONCERN AND APPLICATION

REGULATIONS

The source or sources are suspected of being documented releases from day tank heating oil spill and broken fuel line between a fuel tank and day. There has also been fuel storage at the site since at least the 1960s including barrels and aboveground storage tanks at a tank farm.

The constituents of potential concern (COPC) include the following petroleum-related compounds based on exceedances during previous investigations: DRO, RRO, ethylbenzene, 1-methylnapthalene, acenaphthene, naphthalene, fluorene, and phenanthrene..

Samples collected during the field activities were 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).

3.0 SAMPLING METHODOLOGY

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

May 2026 6

3.1 Soil Sampling Methods

Soil samples were collected using hand tools including a hand auger and shovel. Each soil boring was advanced to the water table and the soil characteristics (e.g., soil type, odor, sheen) were recorded. The analytical soil sample was selected from the soil-water interface, unless there was indication of contamination (i.e., odor, sheen) at a different depth. Field headspace readings were unable to be collected due to the PID malfunctioning in the field. Analytical soil samples were collected immediately upon retrieval and directly from the soil cuttings.

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-milliliters (mL) of methanol, per Alaska (AK) Methods.

3.2 Groundwater Sampling Methods

Since the primary contaminant of concern is diesel and the well diameter is small, a peristaltic pump was used to purge the wells. However, since several wells were dry or purged dry during purging and did not recover to 80% of pre-purge volume, no samples were collected.

4.0 FIELD ACTIVITIES

The field activities were conducted in August 2025 by Qualified Environmental Professionals (QEP), Shayla Marshall and Lexis Goffena. The scope included further site characterization to delineate the lateral and vertical extent of contamination in areas needing further investigation based on the 2024 sample results, and conduct groundwater monitoring of five wells to determine groundwater conditions.

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

4.1 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) died during field activities and the battery was unable to be re-charged.

• Monitoring wells were not sampled due to dry wells or unable to be recharged to 80% of the pre-purge volume.

• RRO analysis was not requested on the chain of custody and, therefore, not analyzed.

• Due to the number of dry wells across the site and/or limited water present in the wells, a groundwater flow direction could not be calculated for the site wells.

4.2 Site Characterization Activities

The site characterization activities included advancing soil test pits, and sampling monitoring wells.

May 2026 7

4.2.1 Test Pits

Test pits were advanced between August 11 and 12, 2025. The test pits were advanced to assess the current soil conditions within the former source area and surrounding areas, and were placed in the following locations:

• Former Tank Farm Samples: Test Pit TP15 (upgradient); Test Pits TP16, TP17, and TP18 (cross gradient and downgradient)

• Former Teacher Housing: Test Pit TP19, TP21 (downgradient), Test Pit TP20 (within footprint)

• Former Day Tanks: Test Pits TP22 (cross gradient), TP23 and TP27 (downgradient)

• Former Pump House: Test Pits TP24, TP25 (cross gradient), TP26 (upgradient)

Test Pit locations are shown in Figure 4. The test pits were advanced to 2 feet bgs, where contamination was previously encountered during past field activities to assess the lateral extent of contamination, beneath a contaminated layer to identify the vertical extent of contamination (Test Pit TP23), or to the maximum depth of the tooling (9.4 feet bgs) to determine if permafrost is present (Test Pit TP26). Hand tools (e.g., hand auger, shovel) were used to advance each test pit.

A total of 15 soil samples plus two duplicates were submitted for analysis. The samples were selected from the depth where contamination was previously encountered, or beneath where there were indication of impact based on odors or visual indications.

4.2.2 Water Level Measurements

Water level measurements were collected for the site’s wells on August 11, 2025, prior to well purging and sampling. The well locations are shown on Figure 5. The water level measurements are provided in Table 1.

Table 1 – Water Level Measurements

Well ID Total Well Depth (ft)

Depth to Water (ft btoc) Development Notes

MW1 1.2 0.63 Purged dry at 100 mL, did not recover to 80% volume; unable to be sampled.

MW2 2.5 1.29

Purged dry at 100 mL, did not recover to 80% volume; unable to be sampled.

MW3 2.5 1.99 (Dry) Not enough water to make through tubing so considered a dry well, unable to be sampled.

MW4 2.5 Dry Dry well. Unable to be sampled.

MW5 2.65 1.98 Purged dry at 10 mL, considered dry, unable to be sampled.

May 2026 8

Table 1 – Water Level Measurements (continued)

Well ID Total Well Depth (ft)

Depth to Water (ft btoc) Development Notes

MW6 2.5 1.43 Purged dry at 100 mL, did not recover to 80% volume; unable to be sampled.

MW7 2.4 1.51 Purged dry at 150 mL, did not recover to 80% volume; unable to be sampled.

MW8 2.7 Dry Dry well. Unable to be sampled.

MW9 2.6 Dry Dry well. Unable to be sampled.

Notes:

Btoc: Below top of casing Ft: Feet

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, 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. Hand tools such as hand augers were dry-deconned using steel brushes between sample locations and then decontaminated using water and Alconox followed with a rinse of potable and deionized water.

A peristaltic pump and disposable tubing were used to develop the groundwater monitoring wells.

Dedicated tubing was used for each well and no pump parts were directly in contact with the groundwater. As a result, it was not necessary to decontaminate the pump and tubing between wells.

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. Brown-black sand as well as some brown-grey silt were encountered beneath peat starting around 1 to 1.5 ft bgs. Permafrost was not encountered. Groundwater was not encountered in any Test Pits. Test Pit TP26 was advanced to 9.4 ft bgs to attempt to find groundwater and permafrost but was not successful. Petroleum odors were noted in Test Pits TP22 and TP23.

5.2 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 of the test pits, except Test Pits TP21, TP25 and TP27.

May 2026 9

DRO, 1-methylnapthalene, 2-methylnapthalene, naphthalene, 1,2,4-trimethylbenzene, carbon tetrachloride, ethylbenzene, and xylenes were reported in one or more samples. DRO was reported at concentrations above cleanup levels in each test pit except TP20, TP21, TP23, TP25, and TP27. The DRO concentrations ranged from 82.6 to 1,160 mg/kg. Unlike the 2024 sample results, no DRO concentrations were greater than the MAC cleanup level.

Samples were collected from TP22 beneath the peat layer where petroleum odors were noted.

This sample contained DRO, multiple PAHs (1-methylnapthalene, 2-methylnapthalene, naphthalene) and volatile organic compounds (VOC) (1,2,4-trimethylbenzene, naphthalene) greater than cleanup levels although the levels were less than the concentration reported in the 2024 sample from Test Pit TP12.

Petroleum odors were also noted in Test Pit TP23. Multiple analytical samples were collected from the test pit, including at the soil interface between the peat and the silt layer (1 foot bgs), where the petroleum odors were strongest (1.5 feet bgs), and where petroleum odors were no longer noted (5.5 feet bgs). While the concentrations of DRO decreased with depth, increases of naphthalene, 1,2,4-trimethylbenzene, ethylbenzene, and xylenes were noted at depth.

Detectable analytical results from the primary soil samples, duplicate soil samples, and one soil trip blank (STB) are listed below in Table 2.

Analyte Analysis Unit Cleanup Level* TP15S4 TP16S4 TP17S4 TP18S4 TP19S4 TP20S4 TP21S4 TP22S4 TP23S2 TP23S3 TP23S10 TP23S20~ TP24S4 TP25S5 TP26S2 TP26S22~ TP27S4 STB

Sample Depth - 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 1.0 1.5 5.5 5.5 2.0 2.5 1.0 1.0 2.0 - Field Headspace PID pppmv - - - - - - - - - - - - - - - 1.1 1.1 - - Diesel Range Organics (DRO) AK102 mg/kg 250 399 351 501 281 674 98.2 131 341 954 346 90.2 82.6 1,160 83 231 564 129 - Polyaromatic Hydrocarbons

1-Methylnaphthalene SW8270E ug/kg 410 33.4 U 30.3 U 29.5 U 23.6 U 35.3 U 201 25.2 U 1,860 68.8 U 27.5 U 138 146 41.1 U 27.2 U 24.4 U 24.1 U 23.3 U - 2-Methylnaphthalene SW8270E ug/kg 1,300 33.4 U 30.3 U 29.5 U 23.6 U 35.3 U 227 25.2 U 2,410 68.8 U 27.5 U 226 237 41.1 U 27.2 U 24.4 U 24.1 U 23.3 U - Acenaphthene SW8270E ug/kg 37,000 33.4 U 30.3 U 29.5 U 23.6 U 35.3 U 78.6 25.2 U 29.2 J 68.8 U 27.5 U 24.8 U 25.5 U 41.1 U 27.2 U 24.4 U 24.1 U 23.3 U - Chrysene SW8270E ug/kg 600,000 33.4 U 30.3 U 29.5 U 23.6 U 35.3 U 25.8 U 25.2 U 26.0 U 68.8 U 27.5 U 11.6 J 25.5 U 41.1 U 27.2 U 24.4 U 24.1 U 23.3 U - Fluoranthene SW8270E ug/kg 590,000 33.4 U 30.3 U 29.5 U 23.6 U 35.3 U 14.8 J 25.2 U 26.0 U 68.8 U 27.5 U 24.8 U 25.5 U 15.3 J 27.2 U 24.4 U 24.1 U 23.3 U - Fluorene SW8270E ug/kg 36,000 13.0 J 12.6 J 14.3 J 23.6 U 35.7 J 28.6 J 25.2 U 76 60.1 J 27.5 U 15.6 J 17.9 J 69.1 27.2 U 24.4 U 10.3 J 23.3 U - Naphthalene SW8270E ug/kg 38 26.7 U 24.2 U 23.6 U 18.9 U 28.3 U 774 20.2 U 1,440 55.1 U 21.1 J 151 126 32.9 U 21.8 U 19.5 U 19.3 U 18.7 U - Phenanthrene SW8270E ug/kg 39,000 33.4 U 30.3 U 29.5 U 23.6 U 35.3 U 32.8 J 25.2 U 27.1 J 68.8 U 27.5 U 9.76 J 9.36 J 41.1 U 27.2 U 24.4 U 24.1 U 23.3 U - Pyrene SW8270E ug/kg 87,000 33.4 U 30.3 U 29.5 U 23.6 U 35.3 U 8.67 J 25.2 U 26.0 U 68.8 U 27.5 U 24.8 U 25.5 U 14.2 J 27.2 U 24.4 U 24.1 U 23.3 U - Other PAHs SW8270E ug/kg varies ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND -

Volatile Organic Compounds 1,2,4-Trimethylbenzene SW8260D ug/kg 610 263 U 240 U 248 U 143 U 409 U 182 U 202 U 2,070 885 U 164 U 363 U 1,050 448 U 164 U 142 U 135 U 137 U 74.9 U 1,3,5-Trimethylbenzene SW8260D ug/kg 660 65.7 U 60.0 U 61.9 U 35.7 U 102 U 22.4 J 50.4 U 617 221 U 41.1 U 90.8 U 258 112 U 41.2 U 35.4 U 33.8 U 34.3 U 18.8 U 4-Isopropyltoluene SW8260D ug/kg - 210 U 192 U 198 U 114 U 327 U 145 U 161 U 163 706 U 131 U 290 U 136 U 358 U 132 U 113 U 108 U 110 U 59.9 U Acetone SW8260D ug/kg 38,000 499 J 515 J 620 U 357 U 978 J 453 U 504 U 358 U 1,610 J 411 U 908 U 425 U 2,570 412 U 261 J 227 J 343 U 188 U Benzene SW8260D ug/kg 22 32.8 U 30.0 U 31.0 U 17.9 U 51.2 U 22.6 U 25.2 U 15.7 J 110 U 20.5 U 45.4 U 21.2 U 55.9 U 20.5 U 17.7 U 16.9 U 17.2 U 9.38 U Carbon tetrachloride SW8260D ug/kg 21 32.8 U 30.0 U 31.0 U 17.9 U 51.2 U 22.6 U 25.2 U 17.9 U 110 U 20.5 U 45.4 U 21.2 U 34.3 J 20.5 U 17.7 U 16.9 U 17.2 U 9.38 U Ethylbenzene SW8260D ug/kg 130 65.7 U 60.0 U 61.9 U 35.7 U 102 U 45.3 U 50.4 U 89.7 221 U 41.1 U 90.8 U 308 112 U 41.2 U 35.4 U 33.8 U 34.3 U 18.8 U Isopropylbenzene (Cumene) SW8260D ug/kg 5,600 65.7 U 60.0 U 61.9 U 35.7 U 102 U 45.3 U 50.4 U 138 221 U 41.1 U 90.8 U 239 112 U 41.2 U 35.4 U 33.8 U 34.3 U 18.8 U Methylene chloride SW8260D ug/kg 330 263 U 240 U 248 U 143 U 409 U 182 U 202 U 143 U 885 U 164 U 194 J 170 U 448 U 164 U 142 U 60.7 J 137 U 74.9 U n-Butylbenzene SW8260D ug/kg 23,000 65.7 U 60.0 U 61.9 U 35.7 U 102 U 45.3 U 50.4 U 315 221 U 41.1 U 90.8 U 98.5 47.7 J 41.2 U 35.4 U 33.8 U 34.3 U 18.8 U n-Propylbenzene SW8260D ug/kg 9,100 65.7 U 60.0 U 61.9 U 35.7 U 102 U 45.3 U 50.4 U 341 221 U 41.1 U 90.8 U 111 112 U 41.2 U 35.4 U 33.8 U 34.3 U 18.8 U Naphthalene SW8260D ug/kg 38 65.7 U 60.0 U 61.9 U 35.7 U 102 U 2,140 50.4 U 2,080 221 U 41.1 U 90.8 U 473 112 U 41.2 U 35.4 U 33.8 U 34.3 U 18.8 U sec-Butylbenzene SW8260D ug/kg 42,000 65.7 U 60.0 U 61.9 U 35.7 U 102 U 45.3 U 50.4 U 253 221 U 41.1 U 90.8 U 39.6 J 112 U 41.2 U 35.4 U 33.8 U 34.3 U 18.8 U Xylenes (total) SW8260D ug/kg 1,500 197 U 180 U 186 U 107 U 307 U 136 U 152 U 579 662 U 123 U 272 U 1,660 335 U 124 U 107 U 101 U 103 U 56.2 U Other VOCs SW8260D ug/kg varies ND ND ND ND ND ND 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

- Not analyzed or no headspace collected due to PID malfunction mg/kg Milligram per kilogram ug/kg Microgram per kilogram

98.2 Analyte detected below MTG Cleanup Level

399 Analyte detected above MTG Cleanup Level

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

Sample ID

May 2026 11

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 E. The ADEC’s 2022 Guidelines for Data Reporting were used for this review. The following is a summary of the quality control (QC) issues affecting data quality or usability.

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

• The limits of detection (LODs) for naphthalene, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, 1,1,2-trichloroethane, 1,2,3-trichlorobenzene, 1,2,3-trichloropropane, 1,2,4-trichlorobenzene, 1,2-dibromoethane, 1,2-dichlorobenzene, 1-2-dichloroethane, 1,2-dichloropropane, 1,4-dichlorobenzene, 2-hexanone, benzene, bromodichloromethane, bromoform, bromomethane, carbon tetrachloride, chloroform, cis-1,2-dichloroethene, cis- 1,3-dichloropropene, dibromochloromethane, dibromomethane, hexachlorobutadiene, methyl-t-butyl-ether, methylene chloride, naphthalene, trans-1,3-dichloropropene, trichloroethene, trichlorofluoromethane, vinyl acetate, and vinyl chloride exceeded the soil ADEC cleanup levels. Since the samples exceeded cleanup levels for other analytes, the data is considered usable for the project purpose of determining if additional investigation or remedial actions are warranted.

• The relative percent difference (RPD) is above the data quality objective (DQO) for sample pairs TP26S2 (primary) and TP26S22 (duplicate). The DRO RPD was 84%. For project purposes, the higher of the two samples is used.

7.0 DISCUSSION

A discussion of the results from the August 2025 soil sampling results are described in further detail below.

7.1 Soil Sampling Discussion

Soil samples were collected from areas where previous samples indicated impacted soil was present. Results indicate there is contamination in the soil above ADEC Method Two Table B2 MTG cleanup levels across the site.

The contamination surrounding the former pump house/old BIA generator building appears defined to the north, west, and east. However, due to the presence of contamination around the former shop and former BIA school, contamination may be co-mingled and the south extent of contamination of the former pump house is not defined.

The contamination to the west and east of the former shop and former schools and the former BIA tank farm remain undefined, although additional step-out samples collected in 2025 are significantly less than the concentrations reported in 2024.

May 2026 12

Previous site activities in 2010 and 2011 encountered permafrost between 1 and 2 feet bgs.

Permafrost was not encountered at those depths in 2024, so a deeper test pit was advanced in 2025 to determine the depth of permafrost at the site. One test pit, TP26, was advanced to a depth of 9.4 feet bgs (the depth of hand auger tooling available). While the soils were wet beginning around

1.5 feet bgs and remained wet to 9.4 feet bgs, no permafrost was encountered. Further, the test pit was allowed to stand overnight and no standing water was present in the test pit. Another test pit was advanced deeper than the previous permafrost levels observed in the past. Test Pit TP23 was advanced to 5.5 feet bgs to determine the vertical depth of contamination. No permafrost was encountered in Test Pit TP23 to the depth of 5.5 feet bgs.

7.2 Groundwater Monitoring Discussion

Analytical samples were not collected from any of the nine site wells. The wells were either dry or did not contain sufficient well volume to be sampled. We understand from locals, the Eek River is tidally influenced. However, the site is on the top of a bluff. Based on TCC’s 2024 drone survey, there is an approximate 14 to 18 feet elevation difference between the Eek River and the project sample locations.

It is possible that due to the soil types encountered at the site (peat above silt/clay) and limited water or low recovery in the site wells, the water encountered across the site is perched water and not groundwater that would be impacted by tidal fluctuations

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 F.

The primary source of contamination at the site are leaks and spills from ASTs and pipelines.

Previous and the 2025 investigations have identified DRO, RRO, ethylbenzene, various PAHs (1-methylnapthalene, 2-methylnapthalene, acenaphthene, naphthalene, fluorene, phenanthrene), and various VOCs (1,2,4-trimethylbenzene, carbon tetrachloride, and xylenes) in the site’s soil. DRO and RRO were also reported at concentrations greater than cleanup levels in the 2024 site wells, noting due to low volume, VOCs and PAHs were not analyzed.

The pathways identified as complete in the CSM include: incidental soil ingestion, dermal absorption of contaminants from soil, ingestion of groundwater, ingestion of wild and farmed foods, and inhalation of outdoor air. Further, much of the site that is contaminated is vegetated so inhalation of fugitive dust, inhalation of indoor air, and direct contact with sediment is not considered potentially complete or warranting further investigation

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.

May 2026 13

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 new granulated activated carbon (GAC) filter and discharged onsite adjacent to the respective sample location. A little over 0.5 gallons (2.07 liters) of water was treated. The GAC bucket remains in TCC’s Anchorage office and will be used for future monitoring events.

• Soil cuttings were not containerized due to all cuttings being used for samples.

Investigation derived waste (IDW) was comprised of gloves, spoons, Ziplock bags, tubing from the groundwater monitoring, and other sampling disposables which were disposed of as solid waste at the Eek landfill.

9.0 CONCLUSIONS AND RECOMMENDATIONS

Petroleum contamination is present at various locations across the site. Step out samples were collected to determine the extent of contamination that was encountered during the 2024 field activities. With the exception of the step outs from the former teacher housing, the 2025 step out samples contained lower concentrations than the 2024 samples. However, the lateral extent of contamination across the site remains undefined, including areas near the west and east property boundary. Based on site observations (odor, staining), the contamination appears to be shallow.

Groundwater samples were not collected in 2025 due to the lack of water in the wells or low recovery. Further, deep test pits did not encounter standing water or permafrost (maximum depth of 9.4 feet bgs).

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

• Additional soil sampling to identify whether contamination extends off property including the areas to the north and west of the tank farm, north of the former teacher housing, between the former teacher housing and former BIA school, and west of the former shop.

• Attempt to collect additional water samples at the site to determine if water is present across the site.

• Addition of RRO analysis for future field activities.

• Conduct sampling at a different time of the year to determine if seasonality impacts the groundwater levels at the site.

• Once the area of contamination has been fully defined, 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).

May 2026 14

10.0 REFERENCES

ADEC. 2013. Monitoring Well Guidance. September.

ADEC. 2017. Guidance on Developing Conceptual Site Models. January.

ADEC. 2024. Field Sampling Guidance. August.

ADEC. 2022. Guidelines for Data Reporting. August 15.

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

Montauk E/E. 2011. Cleanup Report, Eek LKSD Tank Farm, Eek, Alaska. April.

SLR. 2011. Final Property Assessment and Cleanup Plan, Old BIA School Property, Eek, Alaska.

February.

Tanana Commercial Company LLC. 2025. 2024 Site Characterization Report for the Eek Old BIA School and Tanks. April.

Travis/Peterson Environmental Consulting, Inc. 2010. Eek Tank Farms. 30 August.

APPENDIX A

Figures

VICINITY MAP

BAIRD INLET A-1 AND

BETHEL A-8 TOPOS (1954)

EEK OLD BIA SCHOOL AND TANKS

EEK, ALASKA

DATE:

5/24/2026

FIGURE

Project Site

TANANA COMMERCIAL

COMPANY

HISTORIC SOIL SAMPLE

LOCATIONS

EEK OLD BIA SCHOOL AND TANKS

EEK, ALASKA

DATE:

5/24/2026

FIGURE

0 50 100

SCALE IN FEET

N

"New" BIA School

Shop

BIA Tank Farm

Teacher Housing

Pump House / Old BIA Generator Building

Eek River

"Old" BIA School

TANANA COMMERCIAL

COMPANY

LEGEND

Approximate location of 2010 analytical soil sample (TPECI 2010)

Approximate location of former day tank (square) or tank farm AST (circle)

Approximate location of 2010 analytical soil sample (SLR 2011)

GoogleEarth Image: June 6, 2022

Property Boundary US Survey

2021, Lot 2

US Survey 2021, Lot 3

US Survey 2021, Lot 1

Approximate location of 2024 analytical sample (TCC 2024)

GREEN indicates sample concentration less than cleanup levels

RED indicates sample concentration above cleanup levels

2024 MONITORING WELL

SAMPLE RESULTS

EEK OLD BIA SCHOOL AND TANKS

EEK, ALASKA

DATE:

5/24/2026

FIGURE

0 25 50

SCALE IN FEET

N

Former "New" BIA School

Former BIA Tank Farm

Former Teacher Housing

Former Pump House / Old BIA Generator Building

Eek River

Property Boundary

Former "Old" BIA School

TANANA COMMERCIAL

COMPANY

LEGEND

Approximate location of former day tank (square) or tank farm AST (circle) Approximate location of monitoring well that contained concentration(s) of

DRO and/or RRO above the ADEC Table C cleanup level.

MW6

MW7

MW5

MW8

MW9

MW4

MW3

MW1

MW2 / MW22

Former Shop

Approximate location of former structure

Dry

Dry

Dry

Dry

Dry

DRO: 6.63

RRO: 5.48DRO: 0.379 J

RRO: 0.486 J

DRO: 14.1

RRO: 8.33

DRO: 1.47

RRO: 3.27

Reported concentrations noted in milligrams per liter (mg/L).

Approximate location of monitoring well unable to be sampled; dry well.

Approximate location of monitoring well; concentrations below cleanup levels.

DRO: 1.03

RRO: 0.763

GoogleEarth Image: July 20, 2024

2025 SOIL

SAMPLE LOCATIONS

EEK OLD BIA SCHOOL AND TANKS

EEK, ALASKA

DATE:

5/24/2026

FIGURE

0 25 50

SCALE IN FEETN

Former "New" BIA School

Former BIA Tank Farm

Former Teacher Housing

Former Pump House / Old BIA Generator Building

Eek River

Property Boundary

Former "Old" BIA School

TANANA COMMERCIAL

COMPANY

LEGEND

TP6

TP7

TP5

TP8*

TP9

TP4

TP3

TP1 TP2*

Former Shop

TP11

TP12*

TP13

TP14

TP10

Approximate location of former day tank (square) or tank farm AST (circle) RED symbology indicates soil sample that contained concentration(s) above the ADEC Method 2 Migration to Groundwater cleanup level. DRO concentration reported above.

Approximate location of former structure

GoogleEarth Image: July 20, 2024

Approximate location of Test Pit sample collected in July 2024

Approximate location of Test Pit sample collected in August 2025 * Concentration above Maximum Allowable Concentration

TP26

TP15

TP16

TP17

TP18

TP19

TP20

TP21

TP22

TP23

TP24

TP25

BLACK symbology indicates sample location below cleanup levels

TP27

83 mg/kg 183 mg/kg

129 mg/kg

564 mg/kg 1,560 mg/kg

1,220 mg/kg

70.9 mg/kg

244 mg/kg

250,000 mg/kg

341 mg/kg

954 mg/kg34,200 mg/kg

1,160 mg/kg

131 mg/kg 674 mg/kg

395 mg/kg

146 mg/kg

281 mg/kg

501 mg/kg

1,170 mg/kg

780 mg/kg

46.5 mg/kg 351 mg/kg28,000 mg/kg

399 mg/kg

1,340 mg/kg

98.2 mg/kg 774 mg/kg (Naphthalene)

MONITORING WELL

LOCATIONS

EEK OLD BIA SCHOOL AND TANKS

EEK, ALASKA

DATE:

5/24/2026

FIGURE

0 25 50

SCALE IN FEET

N

Former "New" BIA School

Former BIA Tank Farm

Former Teacher Housing

Former Pump House / Old BIA Generator Building

Eek River

Property Boundary

Former "Old" BIA School

TANANA COMMERCIAL

COMPANY

LEGEND

Approximate location of former day tank (square) or tank farm AST (circle)

MW6

MW7

MW5

MW8

MW9

MW4

MW3

MW1

MW2

Former Shop

Approximate location of former structure Approximate location of monitoring well unable to be sampled in 2025;

dry well.

GoogleEarth Image: July 20, 2024

4.3 Decontamination Procedures

Chain of Custody / Sample Receipt Forms