FINAL 

Site Inspection Report 

Blair Hangar Army Aviation Operations Facility 

St. Croix, United States Virgin Islands

Site Inspections for Perfluorooctanoic Acid (PFOA), Perfluorooctanesulfonic Acid (PFOS), 

Perfluorohexanesulfonic Acid (PFHxS), Perfluorononanoic Acid (PFNA), Hexafluoropropylene 

oxide dimer Acid (HFPO-DA) and Perfluorobutanesulfonic Acid (PFBS) 

ARNG Installations, Nationwide

December 2023 

Prepared for: 

Army National Guard Headquarters 

111 S. George Mason Drive 

Arlington, VA 22204 

UNCLASSIFIED
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TABLE OF CONTENTS

Page

LIST OF APPENDICES ................................................................................................................ iii

LIST OF FIGURES ....................................................................................................................... iv

LIST OF TABLES .......................................................................................................................... v

LIST OF ACRONYMS AND ABBREVIATIONS ...................................................................... vi

EXECUTIVE SUMMARY ............................................................................................................ 1

1. INTRODUCTION ............................................................................................... 1-1

1.1 PROJECT AUTHORIZATION ............................................................... 1-1

1.2 SITE INSPECTION PURPOSE .............................................................. 1-1

2. FACILITY BACKGROUND .............................................................................. 2-1

2.1 FACILITY LOCATION AND DESCRIPTION ..................................... 2-1

2.2 FACILITY ENVIRONMENTAL SETTING .......................................... 2-1

2.2.1 Geology ..................................................................................... 2-1

2.2.2 Hydrogeology ........................................................................... 2-2

2.2.3 Hydrology ................................................................................. 2-3

2.2.4 Climate ...................................................................................... 2-3

2.2.5 Current and Future Land Use .................................................... 2-4

2.2.6 Sensitive Habitat and Threatened/Endangered Species ............ 2-4

2.3 HISTORY OF PFAS USE ....................................................................... 2-4

3. SUMMARY OF AREAS OF INTEREST ........................................................... 3-1

3.1 AOI 1 – TRI-MAXTM TRAINING AREA AND AFFF STORAGE AREA

.................................................................................................................. 3-1

3.1.1 Tri-MaxTM Training Area ......................................................... 3-1

3.1.2 AFFF Storage Area ................................................................... 3-1

3.2 ADJACENT SOURCES .......................................................................... 3-1

3.2.1 Former Airport Rescue Fire Fighter Fire Training Area .......... 3-2

3.2.2 ARFF Stations ........................................................................... 3-2

3.2.3 Historic Emergency Responses ................................................. 3-2

4. PROJECT DATA QUALITY OBJECTIVES ..................................................... 4-1

4.1 PROBLEM STATEMENT ...................................................................... 4-1

4.2 INFORMATION INPUTS ....................................................................... 4-1

4.3 STUDY BOUNDARIES ......................................................................... 4-1

4.4 ANALYTICAL Approach ....................................................................... 4-1
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4.5 DATA USABILITY ASSESSMENT ...................................................... 4-2

5. SITE INSPECTION ACTIVITIES ...................................................................... 5-1

5.1 PRE-INVESTIGATION ACTIVITIES ................................................... 5-1

5.1.1 Technical Project Planning ....................................................... 5-2

5.1.2 Utility Clearance ....................................................................... 5-2

5.1.3 Source Water and PFAS Sampling Equipment Acceptability .. 5-2

5.2 SOIL BORINGS AND SOIL SAMPLING ............................................. 5-2

5.3 TEMPORARY WELL INSTALLATION AND GROUNDWATER 

GRAB SAMPLING ................................................................................. 5-4

5.4 SYNOPTIC WATER LEVEL MEASUREMENTS ............................... 5-4

5.5 SURVEYING .......................................................................................... 5-4

5.6 INVESTIGATION-DERIVED WASTE ................................................. 5-5

5.7 LABORATORY ANALYTICAL METHODS ....................................... 5-5

5.8 DEVIATIONS FROM SITE INVESTIGATION UFP-QAPP 

ADDENDUM .......................................................................................... 5-5

6. SITE INSPECTION RESULTS .......................................................................... 6-1

6.1 SCREENING LEVELS ........................................................................... 6-1

6.2 SOIL PHYSICOCHEMICAL ANALYSES ............................................ 6-2

6.3 AOI 1 – Tri-MaxTM Training Area and AFFF Storage Area ................... 6-2

6.3.1 AOI 1 – Soil Analytical Results................................................ 6-2

6.3.2 AOI 1 – Groundwater Analytical Results ................................. 6-3

6.3.3 AOI 1 – Conclusions ................................................................. 6-4

6.4 Cistern sampling results ........................................................................... 6-5

7. EXPOSURE PATHWAYS .................................................................................. 7-1

7.1 SOIL EXPOSURE PATHWAY .............................................................. 7-1

7.1.1 AOI 1 – Tri-MaxTM Training Area and AFFF Storage Area .... 7-1

7.2 GROUNDWATER EXPOSURE PATHWAY........................................ 7-2

7.2.1 AOI 1 – Tri-MaxTM Training Area and AFFF Storage Area .... 7-2

7.3 SURFACE WATER/SEDIMENT EXPOSURE PATHWAY ................ 7-2

7.3.1 AOI 1 – Tri-MaxTM Training Area and AFFF Storage Area .... 7-2

8. SUMMARY AND OUTCOME .......................................................................... 8-1

8.1 SITE INSPECTION ACTIVITIES .......................................................... 8-1
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8.2 OUTCOME .............................................................................................. 8-1

9. REFERENCES .................................................................................................... 9-1

LIST OF APPENDICES

Appendix A. Data Usability Assessment and Data Validation Reports

Appendix B. Field Documentation

 B1. Logs of Daily Notice of Field Activities

 B2. Sampling Forms 

 B3. Survey Data 

 B4. Field Change Request

Appendix C. Photographic Log 

Appendix D. Technical Project Planning Meeting Minutes

Appendix E. Boring Logs and Well Construction Diagrams 

Appendix F. Analytical Results

Appendix G. Laboratory Reports
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LIST OF FIGURES

Figure 2-1. Facility Location

Figure 2-2. Facility Topography 

Figure 2-3. Groundwater Features 

Figure 2-4. Surface Water Features

Figure 2-5. Groundwater Elevations, April 2023 

Figure 3-1. Areas of Interest

Figure 5-1. Site Inspection Sample Locations

Figure 6-1. PFOS Detections in Soil

Figure 6-2. PFOA Detections in Soil

Figure 6-3. PFBS Detections in Soil

Figure 6-4. PFHxS Detections in Soil

Figure 6-5. PFNA Detections in Soil

Figure 6-6. PFOA, PFOS, and PFBS Detections in Groundwater 

Figure 6-7. PFHxS and PFNA Detections in Groundwater 

Figure 7-1. Conceptual Site Model, AOI 1 
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LIST OF TABLES

Table ES-1. Screening Levels (Soil and Groundwater) 

Table ES-2. Summary of Site Inspection Findings and Recommendations 

Table 2-1. June 2017 Blair Hangar Drinking Water Sampling Results 

Table 5-1. Site Inspection Samples by Medium, Blair Hangar AAOF St. Croix, U.S. Virgin 

Islands, Site Inspection Report

Table 5-2. Soil Boring Depths and Temporary Well Screen Intervals, Blair Hangar AAOF

St. Croix, U.S. Virgin Islands Site Inspection Report

Table 5-3. Groundwater Elevation, Blair Hangar AAOF St. Croix, U.S. Virgin Islands, Site 

Inspection Report 

Table 6-1. Screening Levels (Soil and Groundwater) 

Table 6-2. PFOA, PFOS, PFBS, PFNA, and PFHxS Results in Surface Soil, Site 

Inspection Report, Blair Hangar AAOF St. Croix, U.S. Virgin Islands

Table 6-3. PFOA, PFOS, PFBS, PFNA, and PFHxS Results in Shallow Subsurface Soil, 

Site Inspection Report, Blair Hangar AAOF St. Croix, U.S. Virgin Islands

Table 6-4. PFOA, PFOS, PFBS, PFNA, and PFHxS Results in Deep Subsurface Soil, Site 

Inspection Report, Blair Hangar AAOF St. Croix, U.S. Virgin Islands

Table 6-5. PFOA, PFOS, PFBS, PFNA, and PFHxS Results in Groundwater, Site 

Inspection Report, Blair Hangar AAOF St. Croix, U.S. Virgin Islands

Table 8-1. Summary of Site Inspection Findings and Recommendations 
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LIST OF ACRONYMS AND ABBREVIATIONS 

°F Degrees Fahrenheit 

% Percent

μg/kg Microgram(s) per kilogram 

AAOF Army Aviation Operations Facility

AECOM AECOM Technical Services, Inc. 

AFFF Aqueous film-forming foam 

amsl Above mean sea level

AOI Area of interest

ARFF Airport Rescue Fire Fighter

ARNG Army National Guard

bgs Below ground surface 

btoc Below top of casing 

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act 

COC Chain-of-custody 

CSM Conceptual site model

DoD Department of Defense

DPT Direct-push technology

DQO Data quality objective 

DUA Data Usability Assessment

EA EA Engineering, Science, and Technology, Inc., PBC 

ELAP Environmental Laboratory Accreditation Program

EM Engineer Manual 

EB Equipment Blank 

FB Field blank 

FedEx Federal Express

ft Foot (feet)

HDPE High-density polyethylene 

HFPO-DA Hexafluoropropylene oxide dimer acid 

ID Identification

IDW Investigation-derived waste

ITRC Interstate Technology Regulatory Council 

LC/MS/MS Liquid chromatography tandem mass spectrometry

MIL-SPEC Military Specification

MS Matrix spike

MSD Matrix spike duplicate 
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LIST OF ACRONYMS AND ABBREVIATIONS (continued)

ND Non-detect

NELAP National Environmental Laboratory Accreditation Program 

ng/L Nanogram(s) per liter

OSD Office of the Secretary of Defense

PA Preliminary Assessment

PFAS Per- and polyfluoroalkyl substances 

PFBA Perfluorobutanoic acid

PFBS Perfluorobutanesulfonic acid

PFHxA Perfluorohexanoic acid

PFHxS Perfluorohexanesulfonic acid

PFNA Perfluorononanoic acid 

PFOA Perfluorooctanoic acid

PFOS Perfluorooctanesulfonic acid

PFPeA Perfluoropentanoic acid

PFTeDA Perfluorotetradecanoic acid

QAPP Quality Assurance Project Plan

QSM Quality Systems Manual 

RI Remedial investigation 

SI Site inspection

SL Screening level

TOC Total organic carbon 

TPP Technical Project Planning 

UFP Uniform Federal Policy 

U.S. United States

USEPA U.S. Environmental Protection Agency 

VIARNG Virgin Islands Army National Guard
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EXECUTIVE SUMMARY

The Army National Guard (ARNG) G9 is performing Preliminary Assessments (PAs) and Site 

Inspections (SIs) at ARNG facilities nationwide based on the current or potential historical use of 

per- and polyfluoroalkyl substances (PFAS) with a focus on the six compounds presented in the 

memorandum from the Office of the Secretary of Defense (OSD) (Assistant Secretary of 

Defense) dated 6 July 2022. The six compounds listed in the OSD memorandum include 

perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), and 

perfluorobutanesulfonic acid (PFBS), perfluorononanoic acid (PFNA), perfluorohexanesulfonic 

acid (PFHxS), and hexafluoropropylene oxide dimer acid (HFPO-DA)1. These compounds are 

collectively referred to as “relevant compounds” throughout the document and the applicable 

Screening Levels (SLs) are provided below in Table ES-1. 

The PA identified one Area of Interest (AOI), where PFAS-containing materials may have been 

stored, disposed, or released historically (see Table ES-2 for AOI location). The objective of the 

SI is to identify whether there has been a release to the environment from the AOI identified in 

the PA and determine whether further investigation is warranted, a removal action is required to 

address immediate threats, or no further action is required based on SLs for the relevant 

compounds. This SI was completed at the Blair Hangar Army Aviation Operations Facility 

(AAOF) in St. Croix, United States (U.S.) Virgin Islands and determined further evaluation 

under the Comprehensive Environmental Response, Compensation, and Liability Act 

(CERCLA) is warranted for AOI 1. Blair Hangar AAOF will be referred to as the “Facility” 

throughout this document. 

The Facility, operated by the Virgin Islands ARNG encompasses approximately 1.25 acres on 

the south coast of the island of St. Croix, U.S. Virgin Islands. The Facility is located within the 

Henry E. Rohlson International Airport, approximately 45 miles south of Charlotte Amalie, the 

capital of the island of St. Thomas. Occupancy of the ARNG facility began in 1977; however, 

the Blair Hangar wasn’t constructed until 1991. Blair Hangar AAOF is located within the rolling 

plains characteristic of the south-central portion of the island, which is comprised of alluvial 

deposits consisting of gravel, silt and clays. The Facility is currently inactive and has not been 

continuously occupied or used since 2017 due to hurricane damage. Blair Hangar AAOF is 

undergoing construction and is expected to be occupied sometime in the future (AECOM 

Technical Services, Inc. 2020). 

The PA identified one AOI, composed of two potential PFAS release areas, for investigation 

during the SI phase. SI sampling results from the AOI were compared to OSD SLs. Table ES-2

1

1 Of the six PFAS compounds presented in the 6 July 2022 OSD memorandum, HFPO-DA (commonly referred to as 

GenX) was not included as an analyte at the time of this SI. Based on the conceptual site model (CSM) developed 

during the PA and revised based on SI findings, the presence of HFPO-DA is not anticipated at the facility because 

HFPO-DA is generally not a component of military specification (MIL-SPEC) aqueous film forming foam (AFFF) 

and based on its history including distribution limitations that restricted use of GenX, it is generally not a component 

of other products the military used. In addition, it is unlikely that GenX would be an individual chemical of concern 

in the absence of other PFAS.
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summarizes the SI results for the AOI. Based on the results of this SI, and following the 

CERCLA process, a remedial investigation (RI) is warranted for AOI 1.

Table ES-1. Screening Levels (Soil and Groundwater)

Analyte

Residential

(Soil)

(μg/kg)

1 

0-2 ft bgs

Industrial/Commercial

Composite Worker

(Soil)

(μg/kg)

 1 

2-15 ft bgs

Tap Water

(Groundwater)

(ng/L) 1 

PFOA 19 250 6

PFOS 13 160 4

PFBS 1,900 25,000 601

PFHxS 130 1,600 39

PFNA 19 250 6

Notes:

1. Assistant Secretary of Defense. July 2022. Risk Based Screening Levels Calculated for 

Groundwater and Soil using U.S. Environmental Protection Agency’s Regional Screening Level 

Calculator. Hazard Quotient = 0.1. May 2022. 

2. Of the six PFAS compounds presented in the 6 July 2022 OSD memorandum, HFPO-DA 

(commonly referred to as GenX) was not included as an analyte at the time of this SI. Based on the 

CSM developed during the PA and revised based on SI findings, the presence of HFPO-DA is not 

anticipated at the facility because HFPO-DA is generally not a component of MIL-SPEC AFFF 

and based on its history including distribution limitations that restricted use of GenX, it is 

generally not a component of other products the military used. In addition, it is unlikely that GenX 

would be an individual chemical of concern in the absence of other PFAS.

bgs = Below ground surface

μg/kg = Microgram(s) per kilogram

ng/L = Nanogram(s) per liter

Table ES-2. Summary of Site Inspection Findings and Recommendations

AOI

Potential PFAS 

Release Area

Soil

Source Area

Groundwater

Source Area Future Action

1 

Tri-MaxTM Training 

Area and AFFF 

Storage Area

Proceed to RI

Legend:

 = Detected; exceedance of screening levels

 = Detected; no exceedance of screening levels

 = Not detected

Note:

AFFF = Aqueous film-forming foam
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1. INTRODUCTION

1.1 PROJECT AUTHORIZATION

The Army National Guard (ARNG) G9 is the lead agency in performing Preliminary 

Assessments (PAs) and Site Inspections (SIs) at ARNG facilities nationwide based on the current 

or potential historical use of per- and polyfluoroalkyl substances (PFAS) with a focus on six 

compounds presented in the memorandum from the Office of the Secretary of Defense (OSD) 

dated 6 July 2022 (Assistant Secretary of Defense 2022). The six compounds listed in the OSD 

memorandum will be referred to as “relevant compounds” throughout this document and include 

perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorobutanesulfonic 

acid (PFBS), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), and 

hexafluoropropylene oxide-dimer acid (HFPO-DA)2 at ARNG facilities nationwide. The ARNG 

performed this SI at the Blair Hangar Army Aviation Operations Facility (AAOF) in St. Croix, 

United States (U.S.) Virgin Islands. The Blair Hangar AAOF is also referred to as the “Facility”

throughout this document. 

The SI project elements were performed in accordance with the Comprehensive 

Environmental Response, Compensation, and Liability Act (CERCLA) (U.S. Environmental 

Protection Agency [USEPA] 1980), as amended, the National Oil and Hazardous Substances 

Pollution Contingency Plan (40 Code of Federal Regulations Part 300; USEPA 1994), and in 

compliance with U.S. Department of the Army (DA) requirements and guidance for field 

investigations. 

1.2 SITE INSPECTION PURPOSE

A PA was performed at the Blair Hangar AAOF (AECOM Technical Services, Inc. [AECOM] 

2020) that identified one Area of Interest (AOI), composed of two potential PFAS release areas, 

where PFAS-containing materials were used, stored, and/or disposed, or areas where known or 

suspected releases to the environment occurred. The objective of the SI is to identify whether 

there has been a release to the environment from the AOI identified in the PA and determine 

whether further investigation is warranted, a removal action is required to address immediate 

threats, or no further action is required based on screening levels (SLs) for the relevant 

compounds.

2 Of the six PFAS compounds presented in the 6 July 2022 OSD memorandum, HFPO-DA (commonly referred to as 

GenX) was not included as an analyte at the time of this SI. Based on the conceptual site model (CSM) developed 

during the PA and revised based on SI findings, the presence of HFPO-DA is not anticipated at the facility because 

HFPO-DA is generally not a component of military specification (MIL-SPEC) aqueous film forming foam (AFFF) 

and based on its history including distribution limitations that restricted use of GenX, it is generally not a component 

of other products the military used. In addition, it is unlikely that GenX would be an individual chemical of concern 

in the absence of other PFAS.
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2. FACILITY BACKGROUND

2.1 FACILITY LOCATION AND DESCRIPTION

Blair Hangar AAOF is located on the south coast of the island of St. Croix, located 

approximately 45 miles south of Charlotte Amalie, St. Thomas (capital of the U.S. Virgin 

Islands). The island of St. Croix is the largest of the three islands included in the U.S. Virgin

Islands group and is approximately 21 miles long and 6 miles at its widest. The Facility is an 

inactive support installation situated on approximately 1.25 acres (Figure 2-1) located adjacent 

to the Henry E. Rohlsen International Airport. The Facility is surrounded by commercial 

facilities supporting operation of the airport and air services (AECOM 2020).

Limited information regarding the historical use of Blair Hangar AAOF by the Virgin Islands 

ARNG (VIARNG) was found during the PA. The earliest known VIARNG occupancy at the 

Facility goes back to 1977. According to VIARNG personnel, Blair Hangar was built in 1991. 

The Facility maintained both fixed-wing and rotary-wing aircraft; however, more exact details 

were not provided. Maintenance activities at the Facility continued until December 2017, when 

Hurricane Maria struck St. Croix and left Blair Hangar in disrepair. Since that time, Blair Hangar 

has not been continuously occupied or used by the VIARNG, however the AAOF is currently 

undergoing construction and is expected to be occupied in the future. Real estate documentation 

and leasing agreements were not available at the time of the PA (AECOM 2020). 

2.2 FACILITY ENVIRONMENTAL SETTING

The island of St. Croix is generally characterized by mountainous areas in the north and east that 

are flanked by rolling plains to the south. The northern mountainous range dips steeply to the sea 

and forms the northern spine of the island. The eastern range mountains are less rugged and are 

separated by broad low-lying areas. A nearly flat to gently rolling land surface characterizes the 

plains to south and southwest of the Facility (AECOM 2020). 

As seen on Figure 2-1, the Facility is located within the plain in the south-central portion of the

island immediately adjacent to the Caribbean Sea. The topography across the Facility is 

generally flat and is at approximately 75 feet (ft) above mean sea level (amsl). Much of the 

Facility is paved with either asphalt or concrete. Unpaved grassy areas are present along the sides 

of the hangar, apron, and parking area (AECOM 2020). 

The following sections include information on geology, hydrogeology, hydrology, climate, and 

current and future land use. The topography at the Facility is shown on Figure 2-2. The regional 

geology and groundwater features are shown on Figure 2-3. The regional surface water features 

and drainage basins are shown on Figure 2-4. Groundwater elevations and contours are 

presented on Figure 2-5. 

2.2.1 Geology 

The geology of St. Croix includes surficial alluvial deposits with deeper carbonate and volcanic 

parent rock. The north and east mountainous areas are underlain by consolidated volcanic rock 

and sedimentary strata that include volcanic flows and breccia. These formations more
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specifically consist of fine- to coarse-grained tuffaceous sandstone, lapilli tuff, and mudstone. 

The observed volcanic rock is blue to olive gray in color, dense, and is folded and faulted due to 

the island-arc accretion that formed the island (AECOM 2020).

Closer to the Facility, within the central plain, the subsurface geology is comprised of a thin 

layer of alluvial deposits underlain by the Kingshill Limestone and Jealousy Formation. The 

surficial alluvial deposits are composed of gravel, sand, silt, and clay ranging in thickness from 8 

to 76 ft across the plain. Generally, the thickness of the alluvial deposits increases with distance 

from the northern mountainous area. Underlying the alluvial deposits is the Kingshill Limestone, 

which consists of calcareous sediments of limestone and minor dolomite of Pliocene age with 

some silt, sand, and gravel. The formation dips to the southeast and is approximately 50 to 217 ft 

thick across the plain depending on location. The formation is dominated by planktonic 

foraminifera rich carbonate muds, giving it a white to buff appearance. Underlying the Kingshill 

Limestone is the Jealousy Formation. The Jealousy Formation consists of a deep-water limestone 

marl, calcareous clay, and some conglomerate (several thin layers). There is no significant 

difference between the Jealousy Formation and the Kingshill Limestone aside from color, as the 

Jealousy Formation is blue-gray (AECOM 2020).

During the SI, loose, tan and gray, fine-medium sands were observed as the dominant lithology. 

In many of the boreholes interbedded clays of various thickness were observed within the 

fine-medium sands. The borings were completed at depths between 21 and 45 ft below ground 

surface (bgs). Varying quantities of sand were noted, specifically isolated layers of silty sand, 

clayey sand, and sand with gravel were also observed in the borings with thicknesses ranging 

from a few inches to 2 ft. Samples for grain size analyses were collected at one location, 

AOI01-01, and analyzed via American Society for Testing and Materials Method D-422. The 

results indicate that the soil samples are comprised primarily of sand (56.6 percent [%]) and silt

(27.2%). These results and Facility observations are consistent with the reported depositional 

environment of the region. Boring logs are presented in Appendix E and grain size results are 

presented in Appendix F. 

2.2.2 Hydrogeology 

Groundwater underlying the Facility is found in the alluvial deposits and Kingshill Limestone.

The alluvial deposits are moderately permeable and act as temporary storage for rainfall, which

is the primary source of recharge for the shallow aquifer. Information obtained from several 

reports that gauged existing public drinking water wells and private wells in the southern plain 

was assessed to determine depth to groundwater. Depths to water within the alluvial deposits 

across the plain ranged from 5 to 68 ft bgs. The well field in closest proximity to the Facility 

(Golden Grove Well Field) ranges from 13 to 43 ft bgs. In areas where the alluvial deposits are 

saturated, the surficial alluvial aquifer is hydraulically connected to groundwater in the Kingshill 

Limestone beneath. For this reason, the top of the Jealousy Formation is considered to be a 

confining layer and the bottom of the hydrologic unit. The general direction of regional 

groundwater flow across the plain is south-southeast toward the coast (Figure 2-2). Depths to 

water measured in April 2023 during the SI ranged from 12.87 to 14.96 ft bgs. Groundwater 

elevation contours from the SI are presented on Figure 2-5 and indicate the groundwater flow 

direction at the Facility is primarily to the south. No significant pumping wells were identified 

within 0.5 miles. Several well fields exist within 1 mile of the Facility to the north and east (up- 
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and cross-gradient). The nearest of these well fields (Golden Grove Well Field) is located 

approximately 0.75 miles upgradient of the Facility to the northeast, and Fairplains is located 

approximately 1 mile upgradient/cross-gradient to the east (AECOM 2020). 

2.2.3 Hydrology 

Limited surface water features exist on St. Croix. Most streams on the island originate in the

northern mountainous range and flow intermittently. Stream flow rarely reaches the sea before

infiltrating into the alluvial deposits. The closest stream feature to the Facility is the River Gut

system, which is approximately 0.75 miles to the north. Storm runoff is usually a significant part 

of stream flow on the island. Runoff peaks in the hours after the start of a storm and recede 

rapidly. There are no surface water features within the Facility boundary (Figure 2-4) (AECOM

2020). 

Within the boundaries of the Facility are a network of exterior stormwater drains. The drain

system is used to collect stormwater and convey it from the apron to the grassy area surrounding 

the hangar. According to VIARNG personnel, the system is similar to a French drain and 

contains a gravel bottom to facilitate infiltration. Between 2013-2015, a catch basin was added to 

the drainage system to facilitate infiltration and evaporation after storm events (AECOM 2020).

The floor drains found inside Blair Hangar AAOF are believed to drain to the oil/water separator

on the south side of the site and out to the municipal sewer system. No evidence of a treatment 

system was found on-site; therefore, it is assumed that domestic wastewater system is tied to the 

local sewer system (EA Engineering, Science, and Technology, Inc., PBC [EA] 2021a).

Precipitation captured from the roof of the hangar is stored in two concrete underground cisterns

(Figure 2-3). During the PA research, as-built drawings were not provided for the cisterns; it is

unknown how deep the cisterns are set. It is unclear whether the water in the cisterns have any 

communication with groundwater, however based on relevant compound concentrations in 

groundwater samples and from the cistern water samples it is clear that groundwater infiltration 

into the cisterns is at most de minimis. At the time of the site visit, the Facility was not occupied, 

and no personnel were using the water. During the scoping teleconference with Facility

personnel conducted on 12 April 2021, it was determined that the water in the cisterns is used 

primarily for washing aircrafts; however, VIARNG personnel indicated that if the Facility

becomes occupied by more than 25 people, the cisterns will be considered a public drinking 

water source. Based on a review of the USEPA Unregulated Contaminant Monitoring Rule 3 

data, no public water supply has been sampled on the island (AECOM 2020). 

2.2.4 Climate

The climate of St. Croix is tropical, with clearly defined wet and dry seasons. Hot and humid 

weather is common between May and November, with high temperatures between 88 and 90 

degrees Fahrenheit (°F) and low temperatures between 77 and 79°F. During the cooler months 

(December–April), high temperatures reach 82 to 84°F, with low temperatures reaching 72 to 

73°F. Most rainfall occurs during the rainy season, between May and November, and averages 

approximately 40 to 47 inches annually. The rainy season coincides with the Atlantic Ocean

hurricane season, which lasts from June to November. Tropical storms and hurricanes have the 
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highest probability of forming in the months of August, September, and October. These storms 

have the potential to bring strong winds and torrential rain (AECOM 2020). 

2.2.5 Current and Future Land Use

Blair Hangar AAOF is currently unused by the VIARNG and has not been an occupied since 

Hurricane Maria struck St. Croix in September 2017. The Facility is currently under construction

and is expected to be occupied again in the near future (AECOM 2020). A perimeter fence 

surrounds the Facility but has been found to have holes that may allow trespassers to enter 

(AECOM 2020).

2.2.6 Sensitive Habitat and Threatened/Endangered Species

A wildlife survey has not occurred at the Facility, and the Facility does not have any significant 

areas of habitat.

The following species are listed as federally endangered, threatened, proposed, and/or candidate 

species on St. Croix Island, U.S. Virgin Islands (U.S. Fish and Wildlife Services 2022):

• Mammal: West Indian Manatee (Trichechus manatus) – Threatened

• Reptiles: Hawksbill Sea Turtle (Eretmochelys imbricata) – Federally Endangered; 

Leatherback Sea Turtle (Dermochelys coriacea) – Federally Endangered; St. Croix 

Ground Lizard (Ameiva polops) – Federally Endangered 

2.3 HISTORY OF PFAS USE

One AOI, including two potential release areas, were identified in the PA where aqueous 

film-forming foam (AFFF) may have been used, stored, disposed, or released historically at Blair 

Hangar AAOF (AECOM 2020). Interviews and records obtained during the PA indicate that 

regular fire training exercises were performed with AFFF on-site using two Tri-MaxTM 30 

portable fire extinguishing units. Training occurred on an annual basis from approximately 2000 

to 2016. Additionally, AFFF was stored on-site in chemical storage sheds located in the 

northwestern portion of the Facility (AECOM 2020). AFFF may have historically been released 

at the Facility during familiarization training and fire training activities. Additional AFFF 

releases may have occurred from incidental spills in the Tri-MaxTM Training Area and the AFFF 

Storage Area. The potential PFAS release areas were grouped into one AOI based on preliminary 

data and presumed groundwater flow directions. A description of the AOI is presented in 

Section 3.
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Figure 2-1

Facility Location

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Facility Topography

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Groundwater Features

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AOI01-01 = Sample ID

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3. SUMMARY OF AREAS OF INTEREST

The PA evaluated areas where PFAS-containing materials may have been used, stored, disposed, 

or released historically. Based on the PA findings, two potential release areas were identified at

Blair Hangar AAOF and grouped into one AOI identified as: AOI 1. The AOI is shown on 

Figure 3-1. 

3.1 AOI 1 – TRI-MAXTM TRAINING AREA AND AFFF STORAGE AREA

3.1.1 Tri-MaxTM Training Area

According to VIARNG personnel, regular training exercises were performed using Tri-MaxTM

30 portable fire extinguishers. Multiple VIARNG personnel confirmed the Facility had two 

Tri-MaxTM 30 units that were used for training on an annual basis from the early-2000s until 

2016. Training records and personnel accounts of training that took place since 2016 were 

incomplete and unavailable at the time of the PA. Training consisted of spraying AFFF against 

the outside (and occasionally inside) of the northwest hangar bay door in a sweeping motion. The 

reported volume of AFFF released during the training exercises ranged from 1-2 gallons to the 

entire 30-gallon tank. After completion of the training, the expended AFFF was sprayed with 

water into the drain system surrounding the apron on the north side of the hangar. The drain was 

described as a French drain that would allow runoff to easily evaporate or infiltrate into the 

subsurface. Between 2013-2016, a catch basin was added to the drain system to facilitate 

infiltration and evaporation after storm events. Floor drains were observed inside the hangar and 

would have likely captured any AFFF or any other liquids released inside the hangar. No 

as-builts or construction drawings were available during the PA, so it is unclear whether the floor 

drains inside the hangar are connected to the municipal storm drain system located under the 

main road south of the hangar (AECOM 2020). 

3.1.2 AFFF Storage Area

AFFF used in the Tri-MaxTM 30 units was stored in the chemical storage sheds in the northwest

corner of the Facility. According to VIARNG personnel, two 5-gallon buckets of AFFF were 

typically stored in the chemical storage sheds. The timeframe of use and storage of AFFF at the

Facility were unknown at the time of the PA. Additionally, the manufacturer and type of AFFF 

were not known, and previous safety data sheets were lost during Hurricane Maria. Information 

regarding refilling or servicing of the Tri-MaxTM units was unknown at the time of the PA 

interviews. Because AFFF was present within the storage sheds, and little institutional

knowledge regarding the handling and transfer of AFFF was available at the time of the PA, it is 

possible that AFFF may have incidentally been released in this area (AECOM 2020).

3.2 ADJACENT SOURCES

Several potential off-facility sources of PFAS are adjacent to the Facility and are not under the 

control of the VIARNG. The potential adjacent sources are shown on Figure 3-1 and described 

in the following sections for information purposes only. 
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3.2.1 Former Airport Rescue Fire Fighter Fire Training Area

Fire training activities were conducted by the Airport Rescue Fire Fighter (ARFF) team at 

several locations surrounding the Henry E. Rohlsen International Airport runway. Two fire 

training areas were identified by the ARFF Chief and were located on undeveloped land on the 

eastern side of the airport. One was located on the northeast side of the runway and another on 

the southeast of the runway. The exact years of operation and use were not known; however, the 

ARFF Chief recalled that both locations were used from the late-1990s through the early-2000s. 

During this period, training occurred multiple times a year. Typical fire training activities 

consisted of igniting a petroleum-based fuel (avgas, diesel, or gel) and extinguishing it using 

AFFF. It is assumed these training activities occurred using firetrucks and not portable units; 

however, no specific details regarding the source of AFFF were found during the PA. According 

to the ARFF Chief, secondary containment was used during these fire training exercises. It is not 

known if the secondary containment fully captured all AFFF sprayed during training. 

Additionally, it is unknown what happened to the propellent and remaining AFFF in the 

secondary containment after the training exercises (AECOM 2020). These areas are located 

hydraulically cross-gradient of the AOI (EA 2021a). 

3.2.2 ARFF Stations

The current ARFF station opened in 2018 and is located approximately 1,100 ft west of Blair 

Hangar AAOF. The station houses two firetrucks that each store approximately 200 gallons of 

AFFF. According to the ARFF Chief, twice that amount of AFFF is also stored at the station per

Federal Aviation Administration regulations. The AFFF is stored within a closet in the ARFF 

station (AECOM 2020). 

Prior to 2018, the ARFF station was located approximately 2,100 ft east of Blair Hangar AAOF 

and was in operation from 1967-2018. Little information was obtained during the PA regarding

the former ARFF station; however, the ARFF Chief did confirm that the former station stored

AFFF within the building and in firetrucks that were housed in the building. The former ARFF 

station is currently occupied by a moving company and other airport support facilities (AECOM 

2020). 

The ARFF stations are considered hydraulically cross-gradient of the AOI (EA 2021a). 

3.2.3 Historic Emergency Responses

Numerous incidents and plane crashes within the airport property have been historically 

documented by the Federal Aviation Administration and ARFF team. The ARFF Chief was able 

to provide additional information on several crashes that occurred over the last 28 years during 

his time working for the ARFF team. At the time of the PA site visit, the ARFF team was using 

6% AFFF from Chemguard. Specifics regarding the brand, concentration, and volume of AFFF 

used during each incident were not recalled by the ARFF Chief. Details regarding these crashes 

are listed below (AECOM 2020): 

• 1991 Eastern Air Line Tire Fire: after landing and taxiing to the terminal, a tire on an

Eastern Air Line flight caught fire and was extinguished by the ARFF team using AFFF. 
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This emergency response was approximately 500 ft northeast of Blair Hangar AAOF. 

This release area is cross-gradient of the AAOF. 

• 1994 Queen Air Crash: AFFF was used to extinguish a fire on the runway after a Queen

Air crash. This emergency response was approximately 2,000 ft northeast of Blair Hangar 

AAOF. This release area is cross-gradient of the AAOF. 

• 1995 Civil Air Patrol Crash: shortly after take-off a Civil Air Patrol flight crashed

approximately 1,200 ft northeast of the airport runway, outside the property boundary of 

the airport (approximately 5,000 ft northeast of Blair Hangar AAOF). The ARFF team 

responded to the incident and used AFFF to suppress the fire. This release area is cross 

gradient of the AAOF. 

• 2016 Private Plane Crash: AFFF was used to extinguish a fire from a private plane crash 

located approximately 300 ft north of the western end of the airport runway. This 

emergency response was approximately 1,800 ft northwest of Blair Hangar AAOF. This 

release area is cross-gradient of the AAOF.

• 2017 Private Plane Crash: AFFF was used to extinguish a fire from a private plane crash

located approximately 500 ft south of the western end of the airport runway. This 

particular emergency response was 6,000 ft west of Blair Hangar AAOF. This release

area is cross-gradient of the AAOF (AECOM 2020).
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Figure 3-1

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4. PROJECT DATA QUALITY OBJECTIVES

As identified during the data quality objective (DQO) process and outlined in the SI Uniform 

Federal Policy (UFP) Quality Assurance Project Plan (QAPP) Addendum (EA 2021a), the 

objective of the SI is to identify whether there has been a release to the environment at the AOI 

identified in the PA. For each AOI, ARNG determines if further investigation is warranted, a 

removal action is required to address immediate threats, or whether no further action is 

warranted. This SI evaluated groundwater and soil for presence or absence of relevant 

compounds in the sampled AOI. 

4.1 PROBLEM STATEMENT

ARNG will recommend AOIs for remedial investigation (RI) if site-related soil and groundwater 

samples have concentrations of the relevant compounds above the OSD risk-based screening 

levels. The SLs are presented in Section 6.1 of this report. 

4.2 INFORMATION INPUTS

Primary information inputs for the SI include the following:

• The PA Report for Blair Hangar AAOF (AECOM 2020) 

• Analytical data from groundwater and soil samples collected as part of this SI in 

accordance with the site-specific UFP-QAPP Addendum (EA 2021a) 

• Field data collected during the SI, including groundwater elevation and water quality 

parameters measured at the time of sampling.

4.3 STUDY BOUNDARIES

The scope of the SI was bounded horizontally by the property limits of the Facility (Figure 2-2). 

Off-facility sampling was not included in the scope of this SI. If future off-facility sampling is 

required, the proper stakeholders will be notified, and necessary rights of entry will be obtained 

by ARNG with property owner(s). Temporal boundaries were limited to the earliest available 

time field resources were available to complete the study.

4.4 ANALYTICAL APPROACH

Samples were analyzed by Eurofins Lancaster Laboratories Environmental, LLC, accredited 

under the Department of Defense (DoD) Environmental Laboratory Accreditation Program 

(ELAP); Accreditation Number 101 and the National Environmental Laboratory Accreditation 

Program (NELAP); Certificate Number 6408. PFAS data underwent 100% Stage 2B validation 

in accordance with the DoD General Data Validation Guidelines (DA 2019a) and DoD Data 

Validation Guidelines Module 3: Data Validation Procedure of Per- and Polyfluoroalkyl 

Substances Analysis by Quality Systems Manual (QSM) Table B-15 (DA 2020). PFAS data 

were compared to applicable SLs and decision rules as defined in the UFP-QAPP Addendum 

(EA 2021a). 
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4.5 DATA USABILITY ASSESSMENT

The Data Usability Assessment (DUA), which is provided in Appendix A, is an evaluation at the 

conclusion of data collection activities that uses the results of both data verification and 

validation in the context of the overall project decisions or objectives. Using both quantitative 

and qualitative methods, the assessment determines whether project execution and the resulting 

data have met installation-specific DQOs. Both sampling and analytical activities are considered 

to assess whether the collected data are of the right type, quality, and quantity to support the 

decision-making (DA 2019a, 2019b; USEPA 2017). 

Based on the DUA, the environmental data collected during the SI were found to be acceptable 

and usable for this SI evaluation with the qualifications documented in the DUA and its 

associated data validation reports. These data are of sufficient quality to meet the objectives and 

requirements of the UFP-QAPP Addendum (EA 2022a).
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5. SITE INSPECTION ACTIVITIES 

This section describes the environmental investigation and sampling activities that occurred as 

part of the SI. The SI sampling approach was based on the findings of the PA and was 

implemented in accordance with the following approved documents: 

• Final Preliminary Assessment Report, Blair Hangar AAOF, U.S. Virgin Islands, dated 

August 2020 (AECOM 2020)

• Final Programmatic Uniform Federal Policy-Quality Assurance Project Plan, Site 

Inspections for Per- and Polyfluoroalkyl Substances Impacted Sites, ARNG Installations, 

Nationwide, dated December 2020 (EA 2020a)

• Final Site Inspection Uniform Federal Policy-Quality Assurance Project Plan 

Addendum, Blair Hangar AAOF, U.S. Virgin Islands dated January 2022 (EA 2022)

• Final Programmatic Accident Prevention Plan, Revision 1, dated November 2020 

(EA 2020b)

• Final Site Safety and Health Plan, Blair Hangar AAOF, U.S. Virgin Islands, dated 

August 2021 (EA 2021b). 

The SI field activities were conducted from 10 to 17 April 2023 and consisted of direct-push 

technology (DPT) borings and soil sample collection, temporary monitoring well installation, 

and grab groundwater sample collection. Field activities were conducted in accordance with the 

UFP-QAPP Addendum (EA 2021a), except as noted in Section 5.9. 

The following samples were collected during the SI and analyzed for a subset of 24 PFAS via 

liquid chromatography/tandem mass spectrometry (LC/MS/MS) compliant with QSM Version 

5.3 Table B-15 to fulfill the project DQOs:

• Twenty-seven (27) soil samples from 9 soil boring locations 

• Eleven (11) grab groundwater samples from 9 temporary well locations and 2 cisterns 

• Twenty-two (22) quality assurance/quality control samples.

Figure 5-1 provides the sample locations for all media across the Facility. Table 5-1 presents 

the list of samples collected for each medium. Field documentation is provided in Appendix B. 

A log of Daily Notice of Field Activity was completed throughout the SI field activities, which 

is provided in Appendix B1. Additionally, a photographic log of field activities is provided in 

Appendix C. 

5.1 PRE-INVESTIGATION ACTIVITIES

In preparation for the SI field activities, project team members participated in Technical Project 

Planning (TPP) meetings, performed utility clearance, and sampled decontamination source 

water. Details of these activities are presented below. 
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5.1.1 Technical Project Planning

The U.S. Army Corps of Engineers TPP Process, Engineer Manual 200-1-2 (DA 2016a) defines 

four phases to project planning: (1) defining the project phase; (2) determining data needs; (3) 

developing data collection strategies; and (4) finalizing the data collection plan. The process 

encourages stakeholder involvement in the SI, beginning with defining overall project objectives, 

including DQOs, and formulating a sampling approach to address the AOIs identified in the PA. 

A combined TPP Meeting 1 and 2 was held on 6 December 2021, prior to SI field activities. The 

combined TPP Meeting 1 and 2 was conducted in general accordance with Engineer Manual

200-1-2. The stakeholders for this SI include ARNG G-9, USACE, VIARNG, and the U.S. Army 

Corps of Engineers. Stakeholders were provided the opportunity to make comments on the 

technical sampling approach and methods at the combined TPP Meeting 1 and 2. The combined 

TPP Meeting 1 and 2 minutes were memorialized in the UFP-QAPP Addendum (EA 2021a). 

A TPP Meeting 3 was held on 29 November to discuss the results of the SI. Meeting minutes for 

TPP 3 are included in Appendix D of the final report. Future TPP meetings will provide an 

opportunity to discuss the results and findings, and future actions, where warranted. 

5.1.2 Utility Clearance

EA contacted the Utility Notification Center to notify them of intrusive work at the Facility. EA 

contracted Jaca & Sierra, a private utility location service, to perform utility clearance at the 

Facility. Utility clearance was performed at each of the proposed boring locations on 10 April 

2023 with input from the EA field team. General locating services and ground-penetrating radar 

were used to complete the clearance. Additionally, the first 5 ft of each boring were pre-cleared 

by EA’s drilling subcontractor, Jaca & Sierra, using a hand auger to verify utility clearance in 

shallow subsurface where utilities would typically be encountered. 

5.1.3 Source Water and PFAS Sampling Equipment Acceptability

The potable water source on-site which is sourced by the cisterns was chosen for 

decontamination of drilling equipment (identified as BHCIST-02). A sample from this water 

source was taken on 13 April 2023 and analyzed for PFAS by LC/MS/MS compliant with QSM 

5.3 Table B-15. This water had been previously sampled and low levels of PFAS (below SLs) 

were report. As an extra precaution, a 5-gallon carbon unit was used to filter the water prior to its 

use.

Materials that were used within the sampling zone were confirmed as acceptable for use in the

PFAS sampling environment. The checklist of acceptable materials for use in the PFAS sampling 

environment was provided in the Standard Operating Procedures appendix to the Programmatic 

UFP-QAPP (EA 2020a).

5.2 SOIL BORINGS AND SOIL SAMPLING

A total of nine borings were completed during the SI. Soil boring locations are shown on Figure 

5-1. The initial boring locations were selected based on the AOI information provided in the PA 
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(AECOM 2020) and as agreed upon by stakeholders during the TPP and review of the UFPQAPP Addendum (EA 2022). Several boring locations were adjusted within a 50-ft offset to 

accommodate drill rig access, and adjustments were documented in a field change request that 

was approved by ARNG and USACE prior to the start of intrusive activities. This field change 

request is documented in Appendix B4. Samples were generally collected in grass covered areas 

where applicable, to avoid disturbing concrete or asphalt surfaces. Non-dedicated sampling 

equipment (i.e., hand auger) was decontaminated between sampling locations. 

Surface soil samples from 0 to 2 ft bgs were collected from all nine boring locations using a hand 

auger. Subsurface soil samples were collected via DPT drilling methods in accordance with 

Standard Operating Procedure 047 Direct-Push Technology Sampling (EA 2021a). A Geoprobe®

7822DT dual-tube sampling system was used to collect continuous soil cores to the target depth. 

Three discrete soil samples were collected for chemical analysis from each soil boring: one 

sample at the surface (0 to 2 ft bgs) and two subsurface soil samples. One subsurface soil sample 

was collected approximately 1 ft above the groundwater table, and one collected at the mid-point 

between the surface and the groundwater table (not to exceed 15 ft bgs). Groundwater was 

encountered at depths ranging from 12.87 to 14.96 ft bgs during drilling. Total boring 

completion depths, to accommodate temporary well installation, ranged from 20 to 25 ft bgs and 

boring sample depths are provided in Table 5-1. 

During the mobilization, the soil cores were continuously logged for lithological descriptions by 

a field geologist using the Unified Soil Classification System. A photoionization detector was 

used to screen the breathing zone during boring activities as a part of personal safety 

requirements. Observations and measurements were recorded on sampling forms (Appendix B2) 

and in a non-treated field logbook. Depth interval, recovery thickness, photoionization detector 

concentrations, moisture, relative density, Munsell color, and Unified Soil Classification System

texture were recorded. The boring logs are provided in Appendix E. 

Each sample was collected into a laboratory-supplied PFAS-free HDPE bottle and labeled using 

a PFAS-free marker or pen. Samples were packaged on ice and transported via FedEx under 

standard COC procedures to the laboratory and analyzed for PFAS (LC/MS/MS compliant with 

QSM Version 5.3 Table B-15), total organic carbon (TOC) (USEPA Method 9060A) and pH 

(USEPA Method 9045D) in accordance with the UFP-QAPP Addendum (EA 2021a). 

Field duplicate samples were collected at a rate of 10% and analyzed for the same parameters as 

the accompanying samples. Matrix spike (MS)/matrix spike duplicates (MSDs) were collected at 

a rate of 5% and analyzed for the same parameters as the accompanying samples. In instances 

when non-dedicated sampling equipment was used, such as a hand auger for the shallow soil 

samples, one equipment blank (EB) was collected per day and analyzed for the same parameters 

as the soil samples. A temperature blank was placed in each cooler to ensure that samples were 

preserved at or below 6 degrees Celsius during shipment. 

DPT borings were converted to temporary wells, which were subsequently abandoned after 

sampling and surveying in accordance with the UFP-QAPP Addendum (EA 2021a). After 

removal of the casings, boreholes were abandoned using bentonite chips. Borings were installed 

in unpaved areas to avoid disturbing concrete or asphalt surfaces. 
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5.3 TEMPORARY WELL INSTALLATION AND GROUNDWATER GRAB 

SAMPLING

Temporary wells were installed using a GeoProbe® DT325 dual-tube sampling system. Once the 

borehole was advanced to the desired depth, a temporary well was constructed of a 10-ft section 

of 1-inch Schedule 40 polyvinyl chloride screen with sufficient casing to reach the ground 

surface. New polyvinyl chloride pipe and screen were used at each location to avoid cross 

contamination between locations. The screen intervals for the temporary wells are provided in 

Table 5-2. 

Groundwater samples were collected after a period of time following well installation to allow 

groundwater to infiltrate and recharge the temporary well intervals using a peristaltic pump with 

PFAS-free HDPE tubing. Each sample was collected in laboratory-supplied PFAS-free HDPE 

bottles and labeled using a PFAS-free marker or pen. The temporary wells were purged at a rate 

determined in the field to reduce turbidity and draw down prior to sampling. Water quality 

parameters (e.g., temperature, specific conductance, pH, dissolved oxygen, and 

oxidation-reduction potential) were measured using a water quality meter and recorded on the 

field sampling form (Appendix B2) before each grab sample was collected in a separate 

container. Samples were packaged on ice and transported via FedEx under standard COC

procedures to the laboratory and analyzed for PFAS by LC/MS/MS compliant with QSM 

Version 5.3 Table B-15 in accordance with the UFP-QAPP Addendum (EA 2021a). 

Field duplicate samples were collected at a rate of 10% and analyzed for the same parameters as 

the accompanying samples. MS/MSDs were collected at a rate of 5% and analyzed for the same 

parameters as the accompanying samples. Three field blanks (FBs) were collected in accordance 

with the UFP-QAPP Addendum (EA 2021a). One EB was collected per day (a total of eight) and 

analyzed for the same parameters as the groundwater samples. A temperature blank was placed 

in each cooler to ensure that samples were preserved at or below 6 degrees Celsius during 

shipment. 

5.4 SYNOPTIC WATER LEVEL MEASUREMENTS

Groundwater levels were used to monitor Facility-wide groundwater elevations and assess 

groundwater flow. Synoptic water level elevation measurements were collected from the newly 

installed temporary monitoring wells, taken from the survey mark on the northern side of the 

well casing. Groundwater elevation data is provided in Table 5-3. 

5.5 SURVEYING

The northern side of each new temporary well casing was surveyed by Antillean Engineers 

Incorporated, a licensed surveying firm in the Virgin Islands, using a Trimble R10 real-time 

kinematic differential global positioning system. Positions were collected in the applicable 

Universal Transverse Mercator zone projection with World Geodetic System 1984 datum 

(horizontal) and North American Vertical Datum 1988 (vertical). Surveying data were collected 

on 10 April 2023 and are provided in Appendix B3. 
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5.6 INVESTIGATION-DERIVED WASTE

As of the date of this report, the disposal of PFAS investigation-derived waste (IDW) is not 

regulated federally. IDW generated during the SI is considered non-hazardous waste and was 

managed in accordance with the UFP-QAPP Addendum (EA 2021a). 

Soil IDW (i.e., soil cuttings) and liquid IDW (i.e., purge water, development water, and 

decontamination fluids) generated during the SI activities were drummed on-site due to 

suspected petroleum contamination. 

Other solids such as spent personal protective equipment, plastic sheeting, tubing, rope, unused 

monitoring well construction materials, and other environmental media generated during the 

field activities were disposed of at a licensed solid waste landfill. 

5.7 LABORATORY ANALYTICAL METHODS

Samples were analyzed for PFAS by LC/MS/MS compliant with QSM Version 5.3 Table B-15 

at Eurofins Lancaster Laboratories Environmental, LLC, in Lancaster, Pennsylvania, a DoD 

ELAP- and NELAP-certified laboratory. 

Soil samples were also analyzed for TOC using USEPA Method 9060A and pH by USEPA 

Method 9045D. 

5.8 DEVIATIONS FROM SITE INVESTIGATION UFP-QAPP ADDENDUM

Deviations from the UFP-QAPP Addendum occurred based on field conditions. These deviations 

were discussed between EA, ARNG, and USACE. One deviation from the UFP-QAPP 

Addendum is noted below: 

• Several sampling locations had to be adjusted in the field due to utilities. These changes 

are noted in the Field Change Request Form provided in Appendix B4. 
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Table 5-1. Site Inspection Samples by Medium

Blair Hangar AAOF, St. Croix, U.S. Virgin Islands

Site Inspection Report

Sample 

Identification

Sample 

Collection Date

Sample 

Depth

(ft bgs)

PFAS(LC/MS/MS 

compliant with QSM Version 5.3)

TOC(USEPA Method 

9060A)

pH (USEPA 

Method 9045D)

Comments

Soil Samples

AOI01-01-SB-0-2 4/11/2023 0-2 X X X

AOI01-02-SB-0-2 4/11/2023 0-2 X

AOI01-03-SB-0-2 4/11/2023 0-2 X

AOI01-04-SB-0-2 4/11/2023 0-2 X

AOI01-05-SB-0-2 4/11/2023 0-2 X

AOI01-06-SB-0-2 4/11/2023 0-2 X MS/MSD

AOI01-07-SB-0-2 4/11/2023 0-2 X MS/MSD

BHAAOF-01-SB-0-2 4/11/2023 0-2 X

BHAAOF-02-SB-0-2 4/11/2023 0-2 X

AOI01-01-SB-7-8 4/12/2023 7-8 X

AOI01-02-SB-7-9 4/12/2023 7-9 X

AOI01-03-SB-7-9 4/12/2023 7-9 X

AOI01-04-SB-7-9 4/13/2023 7-9 X

AOI01-05-SB-7-9 4/14/2023 7-9 X

AOI01-06-SB-7-9 4/15/2023 7-9 X

AOI01-07-SB-7-9 4/15/2023 7-9 X

BHAAOF-01-SB-7-9 4/13/2023 7-9 X

BHAAOF-02-SB-9-11 4/14/2023 9-11 X

AOI01-01-SB-13-15 4/12/2023 13-15 X

AOI01-02-SB-11-13 4/12/2023 11-13 X

AOI01-03-SB-13-15 4/12/2023 13-15 X

AOI01-04-SB-13-15 4/13/2023 13-15 X

AOI01-05-SB-13-15 4/14/2023 13-15 X

AOI01-06-SB-11-13 4/14/2023 11-13 X

AOI01-07-SB-12-14 4/15/2023 12-14 X

BHAAOF-01-SB-13-15 4/13/2023 13-15 X

BHAAOF-02-SB-21-23 4/14/2023 21-23 X

BHAAOF-DUP-SB-01 4/11/2023 0-2 X X X DUP for AOI01-01-SB-0-2

BHAAOF-DUP-SB-02 4/11/2023 0-2 X DUP for AOI01-05-SB-0-2

BHAAOF-DUP-SB-03 4/11/2023 0-2 X DUP for BHAAOF-02-SB-0-2

Groundwater Samples

AOI01-01-GW 4/13/2023 - X MS/MSD

AOI01-02-GW 4/13/2023 - X

AOI01-03-GW 4/13/2023 - X

AOI01-04-GW 4/13/2023 - X

AOI01-05-GW 4/14/2023 - X

AOI01-06-GW 4/15/2023 - X

AOI01-07-GW 4/15/2023 - X

BHAAOF-01-GW 4/14/2023 - X
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Sample 

Identification

Sample 

Collection Date

Sample 

Depth

(ft bgs)

PFAS(LC/MS/MS 

compliant with QSM Version 5.3)

TOC(USEPA Method 

9060A)

pH (USEPA 

Method 9045D)

Comments

BHAAOF-02-GW 4/15/2023 - X

BHCIST-01-GW 4/13/2023 - X Cistern #1

BHCIST-02-GW 4/13/2023 - X Cistern #2

BHAAOF-DUP-GW-01 4/13/2023 - X DUP for BHCIST-02-GW

BHAAOF-DUP-GW-02 4/13/2023 - X DUP for AOI01-02-GW

Blank Samples

BHAAOF-FB-01 4/13/2023 -

BHAAOF-FB-02 4/14/2023 -

BHAAOF-FB-03 4/15/2023 -

BHAAOF-EB-01 4/11/2023 -

BHAAOF-EB-02 4/12/2023 -

BHAAOF-EB-03 4/13/2023 -

BHAAOF-EB-04 4/13/2023 -

BHAAOF-EB-05 4/14/2023 -

BHAAOF-EB-06 4/14/2023 -

BHAAOF-EB-07 4/15/2023 -

BHAAOF-EB-08 4/15/2023 -

Notes:

DUP = Field duplicate
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Table 5-2. Soil Boring Depths and Temporary Well Screen Intervals

Blair Hangar AAOF, St. Croix, U.S. Virgin Islands

Site Inspection Report

Area of Interest Boring ID

Soil Boring Depth

(ft bgs)

Temporary Well 

Screen Interval

(ft bgs)

1 

AOI01-01 20 15-20

AOI01-02 20 15-20

AOI01-03 20 15-20

AOI01-04 20 15-20

AOI01-05 20 15-20

AOI01-06 20 15-20

AOI01-07 20 15-20

Facility boundary BHAAOF-01 20 15-20

BHAAOF-02 25 15-20

Table 5-3. Groundwater Elevation 

Blair Hangar AAOF, St. Croix, U.S. Virgin Islands

Site Inspection Report

Temporary 

Monitoring 

Well ID

Top of Casing 

Elevation (ft amsl)

Depth to Water

(ft btoc)

Ground Surface 

Elevation (ft amsl)

Groundwater Elevation

(ft amsl)

AOI01-01-GW 19.246 14.96 19.093 4.133

AOI01-02-GW 18.440 14.23 18.526 4.296

AOI01-03-GW 18.030 13.97 17.944 3.974

AOI01-04-GW 18.256 13.92 18.166 4.246

AOI01-05-GW 17.791 13.43 18.020 4.59

AOI01-06-GW 16.112 12.32 16.077 3.757

AOI01-07-GW 16.675 12.87 16.723 3.853

BHAAOF-01-GW 18.313 13.98 18.519 4.539

BHAAOF-02-GW 17.944 13.43 18.027 4.597

Notes: 

1 Temporary well screen set above total depth to capture groundwater interface

btoc = Below top of casing

ID = Identification
Trimax

Training

Area

AFFF

Storage

AOI 1

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

AOI01-07

AOI01-06

BHAAOF-01 BHAAOF-02

BHCIST-01

BHCIST-02

U.S. V.I.

^_

Facility Data

Facility Boundary

Area of Interest

Potential PFAS Release

Sample Locations

Sample Location

Hydrology/Hydrogeology

Groundwater Flow Direction

Stormwater Drainage Flow Direction

Drain

Catch Basin

Cistern

3

0 50

Feet

Data Sources:

ESRI 2021

AECOM 2020

Figure 5-1

Site Inspection Sample Locations

Army National Guard Site Inspections

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Blair Hangar, St. Croix, U.S. Virgin Islands

Path: \\lovetongis\GISdata\Federal\Nationwide\PFAS\MAES_634250383\PROJECTS\SIReport\BlairHangar\BlairHangar.aprx

Date:..........................August 2023

Prepared By:.............................EA

Prepared For:....................USACE

Projection:........WGS 84 UTM 20N
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6. SITE INSPECTION RESULTS

This section presents the analytical results of the SI. The SLs used in this evaluation are

presented in Section 6.1. A discussion of the results for the AOI and boundary areas is provided 

in Sections 6.3 and 6.4. Tables 6-2 through 6-5 present results for soil or groundwater for the 

relevant compounds. Tables that contain all results are provided in Appendix F, and the 

laboratory reports are provided in Appendix G. 

6.1 SCREENING LEVELS

The DoD has adopted a policy to retain facilities in the CERCLA process based on risk-based

SLs for soil and groundwater, as described in a memorandum from the OSD dated 6 July 2022 

(Assistant Secretary of Defense 2022). The ARNG program under which this SI was performed

follows this DoD policy. Should the maximum site concentration for sampled media exceed the 

SLs established in the OSD memorandum, the AOI will proceed to the next phase under 

CERCLA. The SLs established in the OSD memorandum apply to the five compounds presented 

in Table 6-1 below. 

Table 6-1. Screening Levels (Soil and Groundwater)

Analyte

Residential 0 to 2 ft bgs

(Soil)

(μg/kg)1 

Industrial/Commercial

Composite Worker 2 to 15 ft bgs

(Soil)

(μg/kg) 1 

Tap Water

(Groundwater)

(ng/L) 1 

PFOA 19 250 6

PFOS 13 160 4

PFBS 1,900 25,000 601

PFHxS 130 1,600 39

PFNA 19 250 6

Notes:

1. Assistant Secretary of Defense. July 2022. Risk-Based Screening Levels in Groundwater and Soil using 

USEPA’s Regional Screening Level Calculator. Hazard Quotient=0.1. May 2022. 

2. Of the six PFAS compounds presented in the 6 July 2022 OSD memorandum, HFPO-DA (commonly referred 

to as GenX) was not included as an analyte at the time of this SI. Based on the CSM developed during the PA 

and revised based on SI findings, the presence of HFPO-DA is not anticipated at the facility because HFPODA is generally not a component of MIL-SPEC AFFF and based on its history including distribution 

limitations that restricted use of GenX, it is generally not a component of other products the military used. In 

addition, it is unlikely that GenX would be an individual chemical of concern in the absence of other PFAS.

μg/kg = Microgram(s) per kilogram

ng/L = Nanogram(s) per liter

The data in the subsequent sections are compared against the SLs presented in Table 6-1. The 

SLs for groundwater are based on direct ingestion. The SLs for soil are based on incidental 

ingestion and are applied to the depth intervals reasonably anticipated to be encountered by the 

receptors identified at the Facility: the residential scenario is applied to surface soil results (0 to 2 

ft bgs) and the industrial/commercial worker scenario is applied to shallow subsurface soil 

results (2 to 15 ft bgs). The SLs are not applied to deep subsurface soil results (greater than 15 ft 

bgs) because 15 ft is the anticipated limit of construction activities. 
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6.2 SOIL PHYSICOCHEMICAL ANALYSES

To provide basic soil parameter information, soil samples were analyzed for TOC and pH, which 

are important for evaluating transport through the soil medium. Appendix F contains the results 

of the TOC and pH sampling. 

The data collected in this investigation will be used in subsequent investigations, where 

appropriate, to assess fate and transport. According to the Interstate Technology Regulatory 

Council (ITRC), several important PFAS partitioning mechanisms include hydrophobic and 

lipophobic effects, electrostatic interactions, and interfacial behaviors. At relevant environmental 

pH values, certain PFAS are present as organic anions, and are therefore relatively mobile in 

groundwater (Xiao et al., 2015), but tend to associate with the organic carbon fraction that may 

be present in soil or sediment (Higgins and Luthy 2006; Guelfo and Higgins 2013). When 

sufficient organic carbon is present, organic carbon normalized distribution coefficients (Koc 

values) can help in evaluating transport potential, though other geochemical factors (for example, 

pH and presence of polyvalent cations) may also affect PFAS sorption to solid phases (ITRC 

2018). 

Soil grain size, pH, and TOC were analyzed in soil sample AOI01-01-SB- [0-2]. Results showed 

a pH value of 7.6, and a TOC result of 56,000 milligrams per kilogram. The grain size analysis 

indicated 56.6% sand, 27.2% silt, 16.2% gravel, and 0% clay. 

6.3 AOI 1 – TRI-MAXTM TRAINING AREA AND AFFF STORAGE AREA 

This section presents the analytical results for soil and groundwater in comparison to SLs for 

AOI 1, which includes the Tri-MaxTM Training Area and AFFF Storage Area. The detected 

compounds are summarized in Tables 6-2 through 6-5. Figures 6-1 through 6-7 present 

detections for relevant compounds in soil and groundwater. 

6.3.1 AOI 1 – Soil Analytical Results

Tables 6-2 through 6-4 summarize the soil results. Figures 6-1 through 6-7 present the ranges 

of detections in soil.

Soil was sampled at nine boring locations associated with the two potential release areas at AOI 

1. Soil was sampled from three intervals at locations AOI01-01, AOI01-02, AOI01-03, 

AOI01-04, AOI01-05, AOI01-06, and AOI01-07, BHAAOF-01, and BHAAOF-02. Samples 

were generally collected from: surface (0-2 ft bgs), shallow subsurface soil (7 to 9 ft bgs), and 

deep subsurface soil (11 to 15 ft bgs).

Surface soil (0-2 ft bgs) was collected from each soil boring (AOI01-01, AOI01-02, AOI01-03, 

AOI01-04, AOI01-05, AOI01-06, AOI01-07, BHAAOF-01, and BHAAOF-02). Three of the 

five relevant PFAS compounds were detected below their SLs in the surface soil samples. PFBS 

and PFHxS were not detected in any of the surface soil samples. PFOA was detected below the 

SL of 19 μg/kg at AOI01-01, AOI01-03, AOI01-04, and AOI01-07 with the maximum 

concentration of 5.5 μg/kg at AOI01-04. PFNA was detected below the SL of 19 μg/kg in 

surface soil at all soil borings, with the maximum concentration being 10.0 μg/kg at AOI01-04. 
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PFOS was detected below the SL of 13 μg/kg at all soil borings, with the maximum 

concentration being 8.1 μg/kg at AOI01-07. Four of the five relevant PFAS compounds were 

detected below their SLs in the surface soil samples from BHAAOF-01 and BHAAOF-02. PFBS 

was not detected in any of the surface soil samples. PFHxS was detected below the screening 

level (SL) of 130 μg/kg at BHAAOF-02 (0.97 μg/kg). PFNA was detected below the SL of 19 

μg/kg at BHAAOF-01 (0.25 μg/kg) and BHAAOF-02 (0.29 μg/kg). PFOS was detected below 

the SL of 13 μg/kg at BHAAOF-01 (8.3 μg/kg) and BHAAOF-02 (9.4 μg/kg) PFOA was 

detected below the SL of 19 μg/kg at AOI01-07 (0.84 μg/kg) and BHAAOF-01 (1 μg/kg). 

Shallow subsurface soil (7-11 ft. bgs) was collected from each soil boring (AOI01-01, 

AOI01-02, AOI01-03, AOI01-04, AOI01-05, AOI01-06, AOI01-07, BHAAOF-01, and 

BHAAOF-02). Four of the five relevant PFAS compounds were detected in shallow subsurface 

soil. PFBS was not detected in any of the shallow subsurface soil samples. PFHxS was detected 

below the SL of 1,600 μg/kg at AOI01-01 and AOI01-06 with the maximum concentration being 

0.7 μg/kg at AOI01-06. PFNA was detected below the SL of 250 μg/kg at AOI01-02 and AOI01-

04 with the maximum concentration of 0.75 μg/kg at AOI01-02. PFOS was detected below the 

SL of 160 μg/kg at AOI01-02, AOI01-04, AOI01-06, and AOI01-07 with the maximum 

concentration being 1.9 μg/kg at AOI01-02. PFOA was detected below the SL of 250 μg/kg at 

AOI01-02 and AOI01-04 with maximum concentration of 0.68 μg/kg at AOI01-04. At 

BHAAOF-01 and BHAAOF-02, two of the five relevant PFAS compounds were detected below 

the SLs in shallow subsurface soil. PFBS was not detected in any of the shallow subsurface soil 

samples. PFHxS was detected below the SL of 1,600 μg/kg at BHAAOF-02 with a concentration 

of 0.54 μg/kg. PFOS was detected below the SL of 160 μg/kg at BHAAOF-02 with a 

concentration of 0.34 μg/kg. 

Deep subsurface soil (11-23 ft bgs) was collected from each soil boring (AOI01-01, AOI01-02, 

AOI01-03, AOI01-04, AOI01-05, AOI01-06, and AOI01-07). Two of the five relevant PFAS 

compounds were detected in deep subsurface soil. PFBS, PFHxS, and PFNA were not detected 

in any of the deep subsurface soil samples. At AOI01-02, PFOA was detected with a value of 

0.31 μg/kg, and PFOS was detected with a value of 0.4 μg/kg. At BHAAOF-01 and BHAAOF02, none of the relevant PFAS compounds were detected. 

6.3.2 AOI 1 – Groundwater Analytical Results 

Figures 6-6 and 6-7 present the ranges of detections in groundwater. Table 6-5 summarizes the 

groundwater results. 

Groundwater was sampled from seven temporary monitoring wells and two cisterns associated 

with the two potential release areas at AOI 1 (the cisterns are not known to be in communication 

with groundwater, but rather fill with rainwater captured by the roof of the hangar). These 

temporary well locations consist of AOI01-01, AOI01-02, AOI01-03, AOI01-04, AOI01-05, 

AOI01-06, and AOI01-07, and the two cistern locations consist of BHCIST-01 and BHCIST-02. 

Each of the five relevant PFAS compounds were detected at AOI 1, four of these compounds 

being detected above their respective SLs (PFHxS, PFNA, PFOS, and PFOA).
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PFHxS was detected above the SL of 39 ng/L at all temporary wells except for AOI01-05 where 

it was detected below the SL. PFHxS was not detected in samples from either cistern. The 

maximum exceedance concentration detected was 140 ng/L at AOI01-04. 

PFNA was detected above the SL of 6 ng/L at AOI01-04 (7.4 ng/L) and AOI01-07 (10 ng/L), 

and was detected below the SL at all other temporary well locations. PFNA was not detected in 

samples from either cistern.

PFOS was detected above the SL of 4 ng/L at all monitoring wells, the maximum exceedance 

concentration being 280 ng/L at AOI01-04. PFOS was not detected in samples from either 

cistern.

PFOA was detected above the SL of 6 ng/L at all temporary wells except for AOI01-02 and 

AOI01-03, where it was detected below the SL. The maximum exceedance concentration was 

found to be 31 ng/L at AOI01-07. PFOA was detected below the SL in both cisterns, at 0.76 

ng/L at BHCIST-02 and 0.59 ng/L at BHCIST-01. PFOA is the only relevant compound that was 

detected in the two cisterns.

PFBS was detected below the SL of 601 ng/L in samples from each of the seven monitoring 

wells and was not detected in samples from either of the two cisterns. The maximum 

concentration detected was 20 ng/L from AOI01-04. 

Each of the five relevant PFAS compounds were detected at locations BHAAOF-01 and 

BHAAOF-02, three of these compounds being detected above their respective SLs. 

PFBS was detected below the SL of 601 ng/L in samples from both of the temporary monitoring 

wells, with concentrations of 25 ng/L at BHAAOF-01 and 78 ng/L at BHAAOF-02. 

PFHxS was detected above the SL of 39 ng/L at both temporary monitoring wells, with 

concentrations of 190 ng/L at BHAAOF-01 and 570 ng/L at BHAAOF-02. 

PFNA was detected below the SL of 6 ng/L at both wells, with concentrations of 1.9 ng/L at 

BHAAOF-01 and 1.3 ng/L at BHAAOF-02. 

PFOS was detected above the SL of 4 ng/L at both wells, with concentrations of 320 ng/L at 

BHAAOF-01 and 300 ng/L at BHAAOF-02. 

PFOA was detected above the SL of 6 ng/L at both wells, with concentrations of 16 ng/L at 

BHAAOF-01 and 38 ng/L at BHAAOF-02. 

6.3.3 AOI 1 – Conclusions

Based on the results of the SI, four of the five relevant compounds, PFOA, PFOS, PFHxS, and 

PFNA, were detected in soil below their respective SLs. The surface soil samples had the most 

detections, while the deep subsurface soil samples had the fewest. PFOA, PFOS, and PFNA were 

detected below their SLs in surface soil. PFOA, PFOS, PFHxS, and PFNA were detected below 

their SLs in shallow subsurface soil. PFOA and PFOS were detected below their SLs in deep 
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subsurface soil. Since no SL exceedances occurred throughout the sampled soil profile, no 

further evaluation of soil at AOI 1 is necessary.

Four of the five relevant compounds, PFHxS, PFNA, PFOS, and PFOA, were detected above 

their respective SLs in groundwater samples from AOI 1. PFBS was detected below the SL. In 

both cistern samples, PFOA was detected below the SL, and none of the other relevant 

compounds were detected. Since SL exceedances occurred in samples from several of the 

temporary monitoring wells, further evaluation of the groundwater at AOI 1 is warranted. Since 

no SL exceedances occurred within the cistern samples, no further evaluation of the water within 

the cisterns is necessary.

As for the samples collected from BHAAOF-01 and BHAAOF-02, three of the five relevant 

compounds, PFOS, PFHxS, and PFNA, were detected in soil below their respective SLs. The 

surface soil samples had the most detections, while the deep subsurface soil samples had the 

fewest. PFHxS, PFOS, and PFNA were detected below their SLs in surface soil. PFHxS and 

PFOS were detected below their SLs in shallow subsurface soil. None of the relevant compounds 

were detected in deep subsurface soil. Since no SL exceedances occurred throughout the sampled 

soil profile, no further evaluation of soil at the Facility is necessary.

PFHxS, PFOS, and PFOA were detected in groundwater above their respective SLs between 

BHAAOF-01 and BHAAOF-02, and PFBS and PFNA below their SLs. Since SL exceedances 

occurred in the groundwater of both temporary monitoring wells, further evaluation of 

groundwater and the Facility boundary is warranted. 

6.4 CISTERN SAMPLING RESULTS

Sampling of water from both cisterns onsite was performed under the direction of the ARNG in 

June 2017 to assess the potential presence of PFAS in the drinking water source. One sample 

was collected from each cistern and analyzed using USEPA Modified Method 537. A total of 18 

PFAS compounds were analyzed for, and only six PFAS analytes were detected; all other 

analytes were non-detect. Samples were collected from these two cisterns again on 13 April 2023 

to continue to assess presence of PFAS in the cisterns. PFAS concentrations below SLs were 

reported in samples. The cisterns are not currently being used as a drinking water source. 
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Site Inspection Report

Blair Hangar Army Aviation Operations Facility, U.S. Virgin Islands

Table 6-2. PFOA, PFOS, PFBS, PFNA, and PFHxS Results 

Analyte Screening Level1,2 Result Qual Result Qual Result Qual 

PFAS by LC/MS/MS compliant with QSM Version 5.3 Table B-15 (μg/kg)Perfluorobutanesulfonic acid (PFBS) 1900 ND U ND U ND U Perfluorohexanesulfonic acid (PFHxS) 130 ND U ND U ND U Perfluorononanoic acid (PFNA) 19 3.4 3.2 0.93 Perfluorooctanesulfonic acid (PFOS) 13 4 J+ 4.4 J+ 3.4 J+ Perfluorooctanoic acid (PFOA) 19 2 J+ 1.9 J+ ND U Notes:μg/kg = Microgram(s) per kilogram.ft bgs = Feet below ground surface.J = Estimated concentration.J+ = Estimated concentration, biased high.LC/MS/MS = Liquid chromatography tandem mass spectrometryND = Analyte not detected above the LOD (LOD values are presented in Appendix F).PFAS = Per- and polyfluoroalkyl substancesQSM = Quality Systems ManualQual = Qualifier.

Location ID AOI01-01 AOI01-01 AOI01-02 

Sample Name AOI01-01-SB-0-2 BHAAOF-DUP-SB-01 AOI01-02-SB-0-2 

Parent Sample ID AOI01-01-SB-0-2

Sample Date 4/11/2023 4/11/2023 4/11/2023 

Sample Depth (ft bgs) 0-2 0-2 0-2 

Values exceeding the Screening Level are shaded gray.

U = The analyte was not detected at a level greater than or equal to the adjusted Limit

1. Assistant Secretary of Defense. July 2022. Risk-Based Screening Levels in

Groundwater and Soil using EPA’s Regional Screening Level Calculator. HazardQuotient (HQ)=0.1. May 2022.2. The Screening Levels for soil are based on a residential scenario for direct ingestionof contaminated soil.

EA Engineering, Science, and Technology, Inc., PBC
Site Inspection Report

Blair Hangar Army Aviation Operations Facility, U.S. Virgin Islands

Analyte Screening Level1,2

PFAS by LC/MS/MS compliant with QSM Version 5.3 Table B-15 (μg/kg)Perfluorobutanesulfonic acid (PFBS) 1900Perfluorohexanesulfonic acid (PFHxS) 130Perfluorononanoic acid (PFNA) 19Perfluorooctanesulfonic acid (PFOS) 13Perfluorooctanoic acid (PFOA) 19Notes:μg/kg = Microgram(s) per kilogram.ft bgs = Feet below ground surface.J = Estimated concentration.J+ = Estimated concentration, biased high.LC/MS/MS = Liquid chromatography tandem mass spectrometryND = Analyte not detected above the LOD (LOD values are presented in Appendix F).

PFAS = Per- and polyfluoroalkyl substancesQSM = Quality Systems ManualQual = Qualifier.

Location ID

Sample Name

Parent Sample ID

Sample Date

Sample Depth (ft bgs)

Values exceeding the Screening Level are shaded gray.U = The analyte was not detected at a level greater than or equal to the adjusted Limit

1. Assistant Secretary of Defense. July 2022. Risk-Based Screening Levels in

Groundwater and Soil using EPA’s Regional Screening Level Calculator. HazardQuotient (HQ)=0.1. May 2022.2. The Screening Levels for soil are based on a residential scenario for direct ingestion

of contaminated soil.

Table 6-2. PFOA, PFOS, PFBS, PFNA, and PFHxS Results 

Result Qual Result Qual Result Qual 

ND U ND U ND U ND U ND U ND U 

0.34 J 0.41 J 1.1 

1.9 J+ 4.7 J+ 8.1 J+ 

ND U ND U 0.84 J+ 

BHAAOF-DUP-SB-02 AOI01-06-SB-0-2

AOI01-05 AOI01-06 AOI01-07 

AOI01-07-SB-0-2 

4/11/2023

AOI01-05-SB-0-2

4/11/2023 

4/11/2023

0-2 0-2 0-2

EA Engineering, Science, and Technology, Inc., PBC
Site Inspection Report

Blair Hangar Army Aviation Operations Facility, U.S. Virgin Islands

Analyte Screening Level1,2 Result Qual Result Qual Result Qual Result Qual Result Qual 

PFAS by LC/MS/MS compliant with QSM Version 5.3 Table B-15 (μg/kg)Perfluorobutanesulfonic acid (PFBS) 25000 ND UJ ND U ND U ND U ND U 

Perfluorohexanesulfonic acid (PFHxS) 1600 0.45 J ND U ND U ND U ND U Perfluorononanoic acid (PFNA) 250 ND UJ 0.75 ND U 0.23 J ND U Perfluorooctanesulfonic acid (PFOS) 160 ND UJ 1.9 ND U 0.26 J ND U Perfluorooctanoic acid (PFOA) 250 ND UJ 0.31 J ND U 0.68 ND U Notes:μg/kg = Microgram(s) per kilogram.ft bgs = Feet below ground surface.J = Estimated concentration.

J- = Estimated concentration, biased low.LC/MS/MS = Liquid chromatography tandem mass spectrometryPFAS = Per- and polyfluoroalkyl substancesQSM = Quality Systems ManualQual = Qualifier.

Table 6-3. PFOA, PFOS, PFBS, PFNA, and PFHxS Results in Shallow Subsurface Soil, Site Inspectio

Location ID AOI01-01 AOI01-02 AOI01-03 AOI01-04 AOI01-05 

Sample Name AOI01-01-SB-7-8 AOI01-02-SB-7-9 AOI01-03-SB-7-9 AOI01-04-SB-7-9 AOI01-05-SB-7-9 

Parent Sample ID

Sample Date 4/12/2023 4/12/2023 4/12/2023 4/13/2023 4/14/2023 

ND = Analyte not detected above the LOD (LOD values are presented in

Sample Depth (ft bgs) 7-8 7-9 7-9

U = The analyte was not detected at a level greater than or equal to the

adjusted Limit of Detection (LOD).

UJ = The analyte was not detected at a level greater than or equal to the

adjusted LOD. However, the reported adjusted detection limit isapproximate and may be inaccurate or imprecise.1. Assistant Secretary of Defense. July 2022. Risk-Based Screening

Levels in Groundwater and Soil using EPA’s Regional Screening LevelCalculator. Hazard Quotient (HQ)=0.1. May 2022.2. The Screening Levels for soil are based on incidental ingestion of soil

in a industrial/commercial worker scenario.

Values exceeding the Screening Level are shaded gray.

7-9 7-9 

EA Engineering, Science, and Technology, Inc., PBC
Site Inspection Report

Blair Hangar Army Aviation Operations Facility, U.S Virgin Islands Version: FINAL

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Site Inspection Report

Blair Hangar Army Aviation Operations Facility, U.S. Virgin Islands

Location ID

Sample Name

Parent Sample ID

Sample Date

Sample Depth (ft bgs)

Analyte Result Qual Result Qual Result Qual Result Qual Result Qual Result 

PFAS by LC/MS/MS compliant with QSM Version 5.3 Table B-15 (μg/kg)Perfluorobutanesulfonic acid (PFBS) ND U ND U ND U ND U ND U ND Perfluorohexanesulfonic acid (PFHxS) ND U ND U ND U ND U ND U ND Perfluorononanoic acid (PFNA) ND U ND U ND U ND U ND U ND Perfluorooctanesulfonic acid (PFOS) ND U 0.4 J ND U ND U ND U ND Perfluorooctanoic acid (PFOA) ND U 0.31 J ND U ND U ND U ND Notes:μg/kg = Microgram(s) per kilogram.ft bgs = Feet below ground surface.J = Estimated concentration.LC/MS/MS = Liquid chromatography tandem mass spectrometryND = Analyte not detected above the LOD (LOD values are presented in Appendix F).PFAS = Per- and polyfluoroalkyl substancesQSM = Quality Systems ManualQual = Qualifier.U = The analyte was not detected at a level greater than or equal to the adjusted Limit of Detection (LOD).

Table 6-4. PFOA, PFOS, PFBS, PFNA, and PFHxS Results in Deep Subsurface Soil, Site Inspec

AOI01-01 AOI01-02 AOI01-03 AOI01-04 AOI01-05 AO

AOI01-01-SB-13-15 AOI01-02-SB-11-13 AOI01-03-SB-13-15 AOI01-04-SB-13-15 AOI01-05-SB-13-15 AOI01-

4/12/2023 4/12/2023 4/12/2023 4/13/2023 4/14/2023 4/

13-15 11-13 13-15 13-15 13-15 

EA Engineering, Science, and Technology, Inc., PBC
Site Inspection Report

Blair Hangar Army Aviation Operations Facility, U.S Virgin Islands Version: FINAL

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Site Inspection Report

Blair Hangar Army Aviation Operations Facility, U.S. Virgin Islands

Table 6-5. PFOA, PFOS, PFNA, and PFHxS Results in Groundwater, Site Insp

Analyte Screening Level1 Result Qual Result Qual Result Qual Result Qua

PFAS by LC/MS/MS compliant with QSM Version 5.3 Table B-15 (ng/L)Perfluorobutanesulfonic acid (PFBS) 601 17 11 11 10 Perfluorohexanesulfonic acid (PFHxS) 39 130 58 58 53 Perfluorononanoic acid (PFNA) 6 2.7 0.63 J 0.71 J ND UJ 

Perfluorooctanesulfonic acid (PFOS) 4 130 62 60 69 J+ Perfluorooctanoic acid (PFOA) 6 13 2.2 2.3 2.1 J+ 

Notes:J = Estimated concentration.

J- = Estimated concentration, biased low.J+ = Estimated concentration, biased high.LC/MS/MS = Liquid chromatography tandem mass spectrometryng/L = Nanogram(s) per liter.ND = Analyte not detected above the LOD (LOD values are presented in Appendix F).PFAS = Per- and polyfluoroalkyl substancesQSM = Quality Systems ManualQual = Qualifier.Values exceeding the Screening Level are shaded gray.

Location ID AOI01-01 AOI01-02 AOI01-02 AOI01-03 

Sample Name AOI01-01-GW AOI01-02-GW BHAAOF-DUP-GW-02 AOI01-03-GW 

Parent Sample ID AOI01-02-GW

UJ = The analyte was not detected at a level greater than or equal to the adjusted LOD. However, the reported adjusted detection limit is approximate and may be inaccurate or imprecise.

1. Assistant Secretary of Defense. July 2022. Risk-Based Screening Levels inGroundwater and Soil using EPA’s Regional Screening Level Calculator. HazardQuotient (HQ)=0.1. May 2022.U = The analyte was not detected at a level greater than or equal to the adjusted Limit of Detection (LOD).

Sample Date 4/13/2023 4/13/2023 4/13/2023 4/13/2023 

EA Engineering, Science, and Technology, Inc., PBC
Site Inspection Report

Blair Hangar Army Aviation Operations Facility, U.S Virgin Islands Version: FINAL

EA Engineering, Science, and Technology, Inc., PBC 6-14

This page intentionally left blank
Army National Guard Site Inspections

Site Inspection Report

Blair Hangar, St. Croix, U.S. Virgin Islands

Figure 6-1

AOI 1

PFOS Detections in Soil

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06 AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06 AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06

AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

Facility Data

Facility Boundary

Area of Interest

Potential PFAS Release

Hydrology/Hydrogeology

Groundwater Flow Direction

Stormwater Drainage Flow Direction

Drain

Catch Basin

Cistern

3

0 50

Feet

U.S. V.I.

^_

Data Sources:

ESRI 2021

AECOM 2020

Date:..........................August 2023

Prepared By:.............................EA

Prepared For:....................USACE

Projection:........WGS 84 UTM 20N

0 50

Feet

0 50

Feet

Shallow Intermediate Deep

> 1,600

> 160 - 1,600

> 13 - 160

> ND - 13

ND (Non-Detect)

PFOS Results (μg/Kg)

> 1,600

> 160 - 1,600

> 13 - 160

> ND - 13

ND (Non-Detect)

PFOS Results (μg/Kg)

> 1,600

> 160 - 1,600

> 13 - 160

> ND - 13

ND (Non-Detect)

PFOS Results (μg/Kg)

Notes:

PFOS = Perfluorooctanesulfonic acid

Exceedances of the OSD SL are depicted

with a yellow halo. Depth intervals shown

represent respective sampling position

within a given soil boring location.
Site Inspection Report

Blair Hangar Army Aviation Operations Facility, U.S Virgin Islands Version: FINAL

EA Engineering, Science, and Technology, Inc., PBC 6-16

This page intentionally left blank
Figure 6-2

AOI 1

PFOA Detections in Soil

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06 AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06 AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06

AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

Facility Data

Facility Boundary

Area of Interest

Potential PFAS Release

Hydrology/Hydrogeology

Groundwater Flow Direction

Stormwater Drainage Flow Direction

Drain

Catch Basin

Cistern

3

0 50

Feet

U.S. V.I.

^_

0 50

Feet

0 50

Feet

Shallow Intermediate Deep

> 2,500

> 250 - 2,500

> 19 - 250

> ND - 19

ND (Non-Detect)

PFOA Results (μg/Kg)

> 2,500

> 250- 2,500

> 19 - 250

> ND - 19

ND (Non-Detect)

PFOA Results (μg/Kg)

> 2,500

> 250- 2,500

> 19 - 250

> ND - 19

ND (Non-Detect)

PFOA Results (μg/Kg)

Notes:

PFOA = Perfluorooctanoic acid

Exceedances of the OSD SL are depicted

with a yellow halo. Depth intervals shown

represent respective sampling position

within a given soil boring location.

Army National Guard Site Inspections

Site Inspection Report

Blair Hangar, St. Croix, U.S. Virgin Islands

Data Sources:

ESRI 2021

AECOM 2020

Date:..........................August 2023

Prepared By:.............................EA

Prepared For:....................USACE

Projection:........WGS 84 UTM 20N
Site Inspection Report

Blair Hangar Army Aviation Operations Facility, U.S Virgin Islands Version: FINAL

EA Engineering, Science, and Technology, Inc., PBC 6-18

This page intentionally left blank
Figure 6-3

AOI 1

PFBS Detections in Soil

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06 AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06 AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06

AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

Facility Data

Facility Boundary

Area of Interest

Potential PFAS Release

Hydrology/Hydrogeology

Groundwater Flow Direction

Stormwater Drainage Flow Direction

Drain

Catch Basin

Cistern

3

0 50

Feet

U.S. V.I.

^_

0 50

Feet

0 50

Feet

Shallow Intermediate Deep

> 25,000

> 1,900 - 25,000

> 10 - 1,900

> ND - 10

ND (Non-Detect)

PFBS Results (μg/Kg)

> 25,000

> 1,900 - 25,000

> 10 - 1,900

> ND - 10

ND (Non-Detect)

PFBS Results (μg/Kg)

> 25,000

> 1,900 - 25,000

> 10 - 1,900

> ND - 10

ND (Non-Detect)

PFBS Results (μg/Kg)

Notes:

PFBS = Perfluorobutanesulfonic acid

Exceedances of the OSD SL are depicted

with a yellow halo. Depth intervals shown

represent respective sampling position

within a given soil boring location.

Army National Guard Site Inspections

Site Inspection Report

Blair Hangar, St. Croix, U.S. Virgin Islands

Data Sources:

ESRI 2021

AECOM 2020

Date:..........................August 2023

Prepared By:.............................EA

Prepared For:....................USACE

Projection:........WGS 84 UTM 20N
Site Inspection Report

Blair Hangar Army Aviation Operations Facility, U.S Virgin Islands Version: FINAL

EA Engineering, Science, and Technology, Inc., PBC 6-20

This page intentionally left blank
Figure 6-4

AOI 1

PFHxS Detections in Soil

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06 AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06 AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06

AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

Facility Data

Facility Boundary

Area of Interest

Potential PFAS Release

Hydrology/Hydrogeology

Groundwater Flow Direction

Stormwater Drainage Flow Direction

Drain

Catch Basin

Cistern

3

0 50

Feet

U.S. V.I.

^_

0 50

Feet

0 50

Feet

Shallow Intermediate Deep

> 1,600

> 130 - 1,600

> 10 - 130

> ND - 10

ND (Non-Detect)

PFHxS Result (μg/Kg)

> 1,600

> 130 - 1,600

> 10 - 130

> ND - 10

ND (Non-Detect)

PFHxS Result (μg/Kg)

Notes:

PFHxS = Perfluorohexanesulfonic acid

Exceedances of the OSD SL are depicted

with a yellow halo. Depth intervals shown

represent respective sampling position

within a given soil boring location.

> 1,600

> 130 - 1,600

> 10 - 130

> ND - 10

ND (Non-Detect)

PFHxS Result (μg/Kg)

Army National Guard Site Inspections

Site Inspection Report

Blair Hangar, St. Croix, U.S. Virgin Islands

Data Sources:

ESRI 2021

AECOM 2020

Date:..........................August 2023

Prepared By:.............................EA

Prepared For:....................USACE

Projection:........WGS 84 UTM 20N
Site Inspection Report

Blair Hangar Army Aviation Operations Facility, U.S Virgin Islands Version: FINAL

EA Engineering, Science, and Technology, Inc., PBC 6-22

This page intentionally left blank 
Figure 6-5

AOI 1

PFNA Detections in Soil

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06 AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06 AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06

AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

Facility Data

Facility Boundary

Area of Interest

Potential PFAS Release

Hydrology/Hydrogeology

Groundwater Flow Direction

Stormwater Drainage Flow Direction

Drain

Catch Basin

Cistern

3

0 50

Feet

U.S. V.I.

^_

0 50

Feet

0 50

Feet

Shallow Intermediate Deep

> 2,500

> 250 - 2,500

> 19 - 250

> ND - 19

ND (Non-Detect)

PFNA Results (μg/Kg)

> 2 ,500

> 250 - 2,500

> 19 - 250

> ND - 19

ND (Non-Detect)

PFNA Results (μg/Kg)

> 2 ,500

> 250 - 2,500

> 19 - 250

> ND - 19

ND (Non-Detect)

PFNA Results (μg/Kg)

Notes:

PFNA = Perfluorononanoic acid

Exceedances of the OSD SL are depicted

with a yellow halo. Depth intervals shown

represent respective sampling position

within a given soil boring location.

Army National Guard Site Inspections

Site Inspection Report

Blair Hangar, St. Croix, U.S. Virgin Islands

Data Sources:

ESRI 2021

AECOM 2020

Date:..........................August 2023

Prepared By:.............................EA

Prepared For:....................USACE

Projection:........WGS 84 UTM 20N
Site Inspection Report

Blair Hangar Army Aviation Operations Facility, U.S Virgin Islands Version: FINAL

EA Engineering, Science, and Technology, Inc., PBC 6-24

This page intentionally left blank 
Figure 6-6

AOI 1

PFOA, PFOS and PFBS Detections in Groundwater

BHCIST-01

BHCIST-02

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06 AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

BHCIST-01

BHCIST-02

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06 AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

Facility Data

Facility Boundary

Area of Interest

Potential PFAS Release

Hydrology/Hydrogeology

Groundwater Flow Direction

Stormwater Drainage Flow Direction

Drain

Catch Basin

Cistern

3

0 50

Feet

U.S. V.I.

^_

0 50

Feet

PFOA PFOS

BHCIST-01

BHCIST-02

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06

AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

0 50

Feet

PFBS

Note:

PFOA = Perfluorooctanesulfonic acid

PFOS = Perfluorooctanoic acid

PFBS = Perfluorobutanesulfonic acid

Exceedances of the OSD SL are depicted

with a yellow halo.

> 70

> 40 - 70

> 6 - 40

> ND - 6

ND (Non-Detect)

PFOA Results (ng/L)

> 70

> 40 - 70

> 4 - 40

> ND - 4

ND (Non-Detect)

PFOS Results (ng/L)

> 1,000

> 600 - 1,000

> 100 - 600

> ND - 100

ND (Non-Detect)

PFBS Results (ng/L)

Army National Guard Site Inspections

Site Inspection Report

Blair Hangar, St. Croix, U.S. Virgin Islands

Data Sources:

ESRI 2021

AECOM 2020

Date:..........................August 2023

Prepared By:.............................EA

Prepared For:....................USACE

Projection:........WGS 84 UTM 20N
Site Inspection Report

Blair Hangar Army Aviation Operations Facility, U.S Virgin Islands Version: FINAL

EA Engineering, Science, and Technology, Inc., PBC 6-26

This page intentionally left blank 
Figure 6-7

AOI 1

PFHxS and PFNA Detections in Groundwater

BHCIST-01

BHCIST-02

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06 AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

BHCIST-01

BHCIST-02

BHAAOF-02

BHAAOF-01

AOI 1

AOI01-01

AOI01-02

AOI01-04

AOI01-05

AOI01-03

AOI01-06 AOI01-07

Catch Basin

AFFF

Storage Trimax

Training

Area

Cistern

Cistern

Facility Data

Facility Boundary

Area of Interest

Potential PFAS Release

Hydrology/Hydrogeology

Groundwater Flow Direction

Stormwater Drainage Flow Direction

Drain

Catch Basin

Cistern

3

0 50

Feet

U.S. V.I.

^_

Path: \\lovetongis\GISdata\Federal\Nationwide\PFAS\MAES_634250383\PROJECTS\SIReport\BlairHangar\BlairHangar.aprx

0 50

Feet

PFHxS PFNA

Notes:

PFHxS = Perfluorohexanesulfonic acid

PFNA = Perfluorononanoic acid

Exceedances of the OSD SL are depicted

with a yellow halo.

> 1,000

> 100 - 1,000

> 39 - 100

> ND - 39

ND (Non-Detect)

PFHxS Result (ng/L)

> 1,000

> 100 - 1,000

> 6 - 100

> ND - 6

ND (Non-Detect)

PFNA Results (ng/L)

Army National Guard Site Inspections

Site Inspection Report

Blair Hangar, St. Croix, U.S. Virgin Islands

Data Sources:

ESRI 2021

AECOM 2020

Date:..........................August 2023

Prepared By:.............................EA

Prepared For:....................USACE

Projection:........WGS 84 UTM 20N
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7. EXPOSURE PATHWAYS

The conceptual site model (CSM) for the AOI, revised based on the SI findings, is presented on 

Figure 7-1. Please note that while the CSM discussion assists in determining if a receptor may 

be impacted, the decision to move from SI to RI or interim action is determined based upon 

exceedances of the SLs for the relevant compounds and whether the release is more than likely 

attributable to the DoD. A CSM presents the current understanding of the site conditions with 

respect to known and suspected sources, potential transport mechanisms and migration 

pathways, and potentially exposed human receptors. A human exposure pathway is considered 

potentially complete when the following conditions are present: 

1. Contaminant source 

2. Environmental fate and transport

3. Exposure point 

4. Exposure route 

5. Potentially exposed populations.

If any of these elements are missing, the pathway is incomplete. The CSM figure uses an empty 

circle symbol to represent an incomplete exposure pathway. Areas with no identified complete 

pathway generally warrant no further action. However, the pathway is considered potentially 

complete if the relevant compounds are detected, in which case the CSM figure uses a half-filled 

circle symbol to represent a potentially complete exposure pathway. Additionally, a completely 

filled circle symbol is used to indicate when a potentially complete exposure pathway has 

detections of relevant compounds above the SLs. Areas with an identified potentially complete 

pathway that have detections of the relevant compounds above the SLs may warrant further 

investigation. Although the CSM indicates whether potentially complete exposure pathways may 

exist, the recommendation for future study in an RI or no action at this time is based on the 

comparison of the SI analytical results for the relevant compounds to the SLs. 

In general, the potential routes of exposure to the relevant compounds are ingestion and 

inhalation. Human exposure via the dermal contact pathway may occur, and current risk practice 

suggests it is an insignificant pathway compared to ingestion; however, exposure data for dermal 

pathways are sparse and continue to be the subject of toxicological study. The receptors 

evaluated are consistent with those listed in USEPA guidance for risk screening (USEPA 2001). 

Receptors at the Facility include Facility workers, construction workers, and trespassers at the 

Facility. 

7.1 SOIL EXPOSURE PATHWAY 

The SI results for soil were used to determine whether a potentially complete pathway exists 

between the source and potential receptors at AOI 1 based on the aforementioned criteria. 

7.1.1 AOI 1 – Tri-MaxTM Training Area and AFFF Storage Area

From approximately 2000 to 2016, fire training exercises that may have included the release of 

AFFF occurred at the potential release areas associated with AOI 1, the Tri-MaxTM Training 

Area and the AFFF Storage Area. AFFF was also stored in chemical storage sheds located in the 
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northwestern portion of the Facility, and potential incidental spills may have occurred at AOI 1. 

PFOS, PFOA, PFNA, and PFHxS were detected below their respective SLs in soil at AOI 1. 

Based on the results of the SI in AOI 1, ground-disturbing activities to surface soil could result in 

Facility worker and construction worker exposure to the present relevant compounds via 

incidental ingestion, dermal contact, and inhalation of dust. Therefore, the soil exposure pathway 

for Facility workers and construction workers are considered partially complete. The CSM is 

presented on Figure 7-1. 

7.2 GROUNDWATER EXPOSURE PATHWAY

The SI results for the relevant compounds in groundwater were used to determine whether a 

potentially complete pathway exists between the source and potential receptors at each AOI 

based on the aforementioned criteria. 

7.2.1 AOI 1 – Tri-MaxTM Training Area and AFFF Storage Area 

During the time of potential PFAS release associated with AOI 1, expended AFFF was rinsed 

into the drain system surrounding the northern end of the apron, and it was noted on a site visit 

that the French drains extended into the grassy area surrounding the hangar apron. PFAS may 

have been washed into the grassy areas surrounding the apron where it could eventually infiltrate 

shallow groundwater. Since groundwater was found to be at depths less than 15 ft bgs, the 

groundwater ingestion exposure pathway for Facility workers and construction workers is 

considered partially complete. It is also notable that drinking water consumption from the on-site 

cisterns is not actively occurring at this time, but results of the SI did determine that PFOA was 

present in both cisterns at concentrations below the SL. Since groundwater wells located nearby 

the Facility are located either upgradient or side-gradient of the Facility, the pathway for PFAS 

exposure to off-facility residents via ingestion of groundwater is considered incomplete. The 

CSM is presented on Figure 7-1. 

7.3 SURFACE WATER/SEDIMENT EXPOSURE PATHWAY

The SI results for the relevant compounds in groundwater and soil were used to determine 

whether a potentially complete pathway exists between the source and potential receptors at each 

AOI based on the aforementioned criteria.

7.3.1 AOI 1 – Tri-MaxTM Training Area and AFFF Storage Area 

Limited surface water features exist on St. Croix, and the closest stream feature to the Facility is 

the River Gut system, which is approximately 0.75 miles to the north. Storm runoff is usually a 

significant part of stream flow on the island and runoff peaks in the hours after the start of a 

storm and recede rapidly. There are no surface water features within the Facility boundary 

(AECOM 2020) and drainage connects to the sewer system. Due to the limited surface water 

movement within the Facility boundary and near the Facility, the pathway for PFAS exposure to 

receptors via ingestion of surface water or sediment is considered incomplete. The CSM is 

presented on Figure 7-1. 
Notes:

1. The resident receptor refer to off-site 

resident.

AOI 1

PFAS in 

Surface 

Soil

Human 

Activities

Precipitation/

Run-Off

Leaching/Infiltration

Airborne 

Soil 

Particulate

Surface Soil 

at AOI

Surface 

Water/ 

Sediment

Subsurface 

Soil

Shallow 

Groundwater

Ingestion

Ingestion

Ingestion

Ingestion

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

Tri-MaxTM

Training Area 

and AFFF 

Storage Area

SOURCE

Source Release Mechanism Media

PATHWAY

Transport

and Migration Media Exposure Routes

Inhalation 

of Dust

Potentially Complete Pathway with Exceedance of Screening Level

PFAS in 

Subsurface 

Soil
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8. SUMMARY AND OUTCOME

This section summarizes SI activities and findings. The most significant findings are summarized 

in this section and are reproduced directly or abstracted from information contained in this 

report. The outcome provides general and comparative interpretations of the findings relative to 

the SLs. 

8.1 SITE INSPECTION ACTIVITIES 

The SI field activities at the Facility were conducted from 10 to 17 April 2023. The SI field 

activities included soil sample collection, temporary monitoring well installation, grab 

groundwater sample collection, and land surveying. Field activities were conducted in 

accordance with the UFP-QAPP Addendum (EA 2021a). 

To fulfill the project DQOs set forth in the approved SI UFP-QAPP Addendum (EA 2021a), 

samples were collected and analyzed for a subset of PFAS by LC/MS/MS compliant with QSM 

Version 5.3 Table B-15 as follows: 

• Twenty-seven (27) soil samples from 9 soil boring locations

• Eleven (11) grab groundwater samples from 9 temporary well locations and 2 cisterns 

• Twenty-two (22) quality assurance/quality control samples.

An SI is conducted when the PA determines an AOI exists based on probable use, storage, and/or 

disposal of PFAS-containing materials. The SI includes multi-media sampling at AOIs to 

determine whether or not a release has occurred. The SI may conclude further investigation is 

warranted, a removal action is required to address immediate threats, or no further action is 

required. Additionally, the CSMs were refined to assess whether a potentially complete pathway

exists between the source and potential receptors for potential exposure at the AOIs, which are

described in Section 7. 

8.2 OUTCOME

Based on the results of this SI, further evaluation under CERCLA in the form of an RI is 

warranted for AOI 1. Based on the CSMs developed and revised based on the SI findings, there 

is potential for exposure to soil and groundwater from releases during historical DoD activities at 

the Facility, and potentially from off-facility sources. Sample analytical concentrations collected 

during this SI were compared against the project SLs in soil and groundwater, as described in 

Table 6-1. A summary of the results of the SI data relative to SLs is as follows:

• AOI 1:

 Four of the five relevant compounds (PFOS, PFOA, PFNA, and PFHxS) were 

detected in groundwater above their respective SLs in the source areas and near the 

Facility boundary at AOI 1. PFBS was detected at concentrations below the SL. 
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 Four of the five relevant compounds (PFOS, PFOA, PFNA, and PFHxS) were 

detected below their respective SLs in the soil profile. 

Of the six PFAS compounds presented in the 6 July 2022 OSD memorandum, HFPO-DA 

(commonly referred to as GenX) was not included as an analyte at the time of this SI. Based on 

the CSM developed during the PA and revised based on SI findings, the presence of HFPO-DA 

is not anticipated at the facility because HFPO-DA is generally not a component of MIL-SPEC 

AFFF and based on its history including distribution limitations that restricted use of GenX, it is 

generally not a component of other products the military used. In addition, it is unlikely that 

GenX would be an individual chemical of concern in the absence of other PFAS.

Table 8-1 summarizes the SI results for soil and groundwater used to determine if an AOI should 

be considered for further investigation under CERCLA and undergo an RI. 

Table 8-1. Summary of Site Inspection Findings and Recommendations

AOI

Potential PFAS 

Release Area

Soil

Source Area

Groundwater

Source Area Future Action

1 

Tri-MaxTM Training 

Area and AFFF 

Storage Area

Proceed to RI

Legend:

 = Detected; exceedance of screening levels

 = Detected; no exceedance of screening levels

 = Not detected

Note:

AFFF = Aqueous film-forming foam
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9. REFERENCES

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August.

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Department of the Army (DA). 2016a. EM-200-1-2, Environmental Quality, Technical Project 

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———. 2019a. Department of Defense (DoD), Department of Energy (DOE) Consolidated

Quality Systems Manual (QSM) for Environmental Laboratories, Version 5.3. May. 

. 2019b. General Data Validation Guidelines. November. 

. 2020. Data Validation Guidelines Module 3: Data Validation Procedure for Per- and 

Polyfluoroalkyl Substances Analysis by QSM Table B-15. May.

EA Engineering, Science, and Technology, Inc., PBC (EA). 2020a. Final Programmatic 

Uniform Federal Policy Quality Assurance Project Plan, Site Inspections for Per- and 

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.2020b. Final Programmatic Accident Prevention Plan, Revision 1. November.

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Installations, Nationwide. August. 

.2021b. Final Site Safety and Health Plan, Blair Hangar AAOF, U.S. Virgin Islands. 

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Higgins, C.P., and R.G. Luthy. 2006. Sorption of perfluorinated surfactants on sediments. 

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Interstate Technology Regulatory Council (ITRC). 2018. Environmental Fate and Transport for 

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. 1994. National Oil and Hazardous Substances Pollution Contingency Plan (Final Rule).

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. 2006. Guidance on Systematic Planning Using the Data Quality Objectives Process

USEPA/240/B-06/001. February. 

. 2017. National Functional Guidelines for Organic Superfund Data Review. OLEM 

9355.0-136, EPA-540-R-2017-002. Office of Superfund Remediation and Technology 

Innovation. January.

U.S. Fish and Wildlife Service. 2023. Endangered Species. http://ecos.fws.gov/ipac/. 21 July. 

Xiao, F., M. F. Simcik, T.R. Halbach, and J.S Gulliver. 2015, Perfluorooctane sulfonate (PFOS) 

and perfluorooctanoate (PFOA) in soils and groundwater of a U.S. metropolitan area: 

Migration and implications for human exposure. Water Research 72:64-74.