FINAL

Site Inspection Report 

Waiawa Gulch Training Site and 

Unit Training and Equipment Site

O‘ahu, Hawai‘i

Site Inspection for Perfluorooctanoic acid (PFOA), 

Perfluorooctanesulfonic acid (PFOS), Perfluorohexanesulfonic 

acid (PFHxS), Perfluorononanoic acid (PFNA), 

Hexafluoropropylene oxide dimer acid (HFPO-DA), and 

Perfluorobutanesulfonic acid (PFBS) at ARNG Installations, 

Nationwide

May 2023

Prepared for:

Army National Guard Bureau

111 S. George Mason Drive

Arlington, VA 22204

UNCLASSIFIED
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Table of Contents

Executive Summary ..............................................................................................................ES-1

1. Introduction ..................................................................................................................1-1

1.1 Project Authorization .............................................................................................1-1

1.2 SI 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 Firetruck Pump Test Area ............................................................................3-1

3.2 AOI 2 Vehicle Maintenance Area, Firetruck Parking Area, and Storage 

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

3.3 Adjacent Sources ..................................................................................................3-1

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

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 ..........................................................................5-1

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

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

5.2 Soil Borings and Soil Sampling .............................................................................5-2

5.3 Permanent Well Installation and Groundwater Sampling.......................................5-4

5.4 Synoptic Water Level Measurements ....................................................................5-5

5.5 Surveying..............................................................................................................5-5

5.6 Investigation-Derived Waste..................................................................................5-5

5.7 Laboratory Analytical Methods ..............................................................................5-5

5.8 Deviations from SI 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.....................................................................................................................6-2

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

6.3.2 AOI 1 Groundwater Analytical Results.........................................................6-2

6.3.3 AOI 1 Conclusions ......................................................................................6-3
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6.4 AOI 2.....................................................................................................................6-3

6.4.1 AOI 2 Soil Analytical Results .......................................................................6-3

6.4.2 AOI 2 Groundwater Analytical Results.........................................................6-3

6.4.3 AOI 2 Conclusions ......................................................................................6-4

7. Exposure Pathways......................................................................................................7-1

7.1 Soil Exposure Pathway .........................................................................................7-1

7.1.1 AOI 1...........................................................................................................7-1

7.1.2 AOI 2...........................................................................................................7-2

7.2 Groundwater Exposure Pathway...........................................................................7-2

7.2.1 AOI 1...........................................................................................................7-2

7.2.2 AOI 2...........................................................................................................7-2

7.3 Surface Water and Sediment Exposure Pathway ..................................................7-3

7.3.1 AOI 1...........................................................................................................7-3

7.3.2 AOI 2...........................................................................................................7-3

8. Summary and Outcome................................................................................................8-1

8.1 SI Activities............................................................................................................8-1

8.2 Outcome ...............................................................................................................8-1

9. References...................................................................................................................9-1
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Appendices

Appendix A Data Usability Assessment and Validation Reports 

Appendix B Field Documentation

B1. Log of Daily Notice of Field Activities 

B2. Sampling Forms

B3. Monitoring Well Development Forms 

B4. Field Change Request Forms

B5. Survey Data

Appendix C Photographic Log

Appendix D TPP Meeting Minutes

Appendix E Boring Logs and Well Construction Forms 

Appendix F Analytical Results

Appendix G Laboratory Reports

Figures

Figure 2-1 Facility Location

Figure 2-2 Facility Topography

Figure 2-3 Groundwater Features

Figure 2-4 Groundwater Elevations, April 2022

Figure 2-5 Surface Water Features

Figure 3-1 Areas of Interest

Figure 5-1 Site Inspection Sample Locations

Figure 6-1 PFOA Detections in Soil

Figure 6-2 PFOS 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 and AOI 2

Tables

Table ES-1 Screening Levels (Soil and Groundwater)

Table ES-2 Summary of Site Inspection Findings and Recommendations

Table 5-1 Site Inspection Samples by Medium

Table 5-2 Soil Boring Depths, Permanent Monitoring Well Screen Intervals, and

Groundwater Elevations

Table 6-1 Screening Levels (Soil and Groundwater)

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

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

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

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

Table 8-1 Summary of Site Inspection Findings and Recommendations
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Acronyms and Abbreviations

% percent

°C degrees Celsius

°F degrees Fahrenheit

μg/kg micrograms per kilogram

AECOM AECOM Technical Services, Inc.

AFFF aqueous film-forming foam

amsl above mean sea level

AOI Area of Interest

ARNG Army National Guard

bgs below ground surface 

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act 

CoC chain of custody

CSM conceptual site model

CWRM Commission on Water Resource Management

DA Department of the Army

DoD Department of Defense

DO dissolved oxygen

DON Department of the Navy

DOT Department of Transportation

DPT direct push technology

DQO data quality objective

DUA data usability assessment

EA EA Engineering, Science, and Technology, Inc.

EDRTM Environmental Data Resources, Inc.TM

ELAP Environmental Laboratory Accreditation Program

EM Engineer Manual

FedEx Federal Express

GPRS Ground Penetrating Radar Systems

HDOH Hawai‘i Department of Health

HDPE high-density polyethylene 

HEER Hazard Evaluation and Emergency Response Office

HFPO-DA hexafluoropropylene oxide dimer acid

HIARNG Hawai‘i Army National Guard

IDW investigation-derived waste

ISM Incremental Sample Methodology

ITRC Interstate Technology Regulatory Council

kg kilogram

LC/MS/MS liquid chromatography with tandem mass spectrometry

MIL-SPEC military specification

NELAP National Environmental Laboratory Accreditation Program

ng/L nanograms per liter

NOAA National Oceanic and Atmospheric Administration

NTU nephelometric turbidity units 
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ORP oxidation-reduction potential

OSD Office of the Secretary of Defense

PA Preliminary Assessment

PFAS per- and polyfluoroalkyl substances

PFBS perfluorobutanesulfonic acid

PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

PID photoionization detector

PQAPP Programmatic UFP-QAPP

PVC polyvinyl chloride

QA quality assurance

QAPP Quality Assurance Project Plan

QC quality control

QSM Quality Systems Manual

RI Remedial Investigation

SI Site Inspection

SL screening level

SOP standard operating procedure

TGM Technical Guidance Manual

TOC total organic carbon

TPP Technical Project Planning

UFP Uniform Federal Policy

US United States

USACE United States Army Corps of Engineers

USCS Unified Soil Classification System

USEPA United States Environmental Protection Agency

USFWS United States Fish and Wildlife Service

UTES Unit Training and Equipment Site
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Executive Summary

The Army National Guard (ARNG) G-9 is performing Preliminary Assessments (PAs) and Site 

Inspections (SIs) 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) dated 6 July 2022 (Assistant Secretary of Defense, 2022). The six 

compounds listed in the OSD memorandum include perfluorooctanesulfonic acid (PFOS), 

perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid 

(PFHxS), hexafluoropropylene oxide dimer acid (HFPO-DA)1

, and perfluorobutanesulfonic acid 

(PFBS). These compounds are collectively referred to as “relevant compounds” throughout the 

document, and the applicable screening levels (SLs) are provided in Table ES-1. 

The PA identified two Areas of Interest (AOIs) where PFAS-containing materials may have been 

used, stored, disposed, or released historically (see Table ES-2 for AOI locations). The objective 

of the SI is to identify whether there has been a release to the environment from the AOIs 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 relevant 

compounds. This SI was completed at the Waiawa Gulch Training Site and Unit Training and 

Equipment Site (UTES) in O‘ahu, Hawai‘i and determined further evaluation under the 

Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) is 

warranted for AOI 1 and AOI 2. The Waiawa Gulch Training Site and UTES will also be referred 

to as the “facility” throughout this document.

The Waiawa Gulch Training Site and UTES facility is located north of Pearl Harbor, on the island 

of O‘ahu. The facility falls 0.75 miles northeast of the H1-H2 freeway merge. The facility is 

bordered to the north and south by industrial activities and to the west by a privately operated 

junk yard. The Waiawa Gulch Training Site and UTES facility comprise approximately 20 acres.

The PA identified two AOIs for investigation during the SI phase. SI sampling results from the two 

AOIs were compared to OSD SLs. Table ES-2 summarizes the SI results for each AOI. Based on 

the results of this SI, further evaluation under CERCLA is warranted in a Remedial Investigation

(RI) for AOI 1 and AOI 2.

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

Analyteb

Residential

(Soil)

(μg/kg)a 

0-2 feet bgs

Industrial/ Commercial 

Composite Worker

(Soil)

(μg/kg)a 

2-15 feet bgs

Tap Water

(Groundwater)

(ng/L)a

PFOA 19 250 6

PFOS 13 160 4 

PFBS 1,900 25,000 601 

PFHxS 130 1,600 39

PFNA 19 250 6

Notes:

bgs = below ground surface; μg/kg = micrograms per kilogram; ng/L = nanograms per liter

a.) Assistant Secretary of Defense, 2022. Risk Based Screening Levels in Groundwater and Soil using United States Environmental Protection 

Agency’s (USEPA’s) Regional Screening Level Calculator. Hazard Quotient (HQ) = 0.1. 6 July 2022. 

b.) 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 HFPODA 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 ES-2: Summary of Site Inspection Findings and Recommendations

AOI Potential 

Release Area

Soil –

Source Area

Groundwater –

Source Area Future Action

1 Firetruck Pump Test Area Proceed to RI 

2 Firetruck Parking Area, Vehicle 

Maintenance Area, and Storage Buildings Proceed to RI 

Legend:

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected
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1. Introduction

1.1 Project Authorization

The Army National Guard (ARNG) G-9 is the lead agency in performing Preliminary Assessments 

(PAs) and Site Inspections (SIs) 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) 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 perfluorooctanoic acid (PFOA), 

perfluorooctanesulfonic acid (PFOS), perfluorohexanesulfonic acid (PFHxS), perfluorononanoic 

acid (PFNA), hexafluoropropylene oxide dimer acid (HFPO-DA)1

, and perfluorobutanesulfonic 

acid (PFBS) at ARNG facilities nationwide. The ARNG performed this SI at the Waiawa Gulch 

Training Site and Unit Training and Equipment Site (UTES) in O‘ahu, Hawai‘i. The Waiawa Gulch 

Training Site and UTES will also be referred to as the “facility” throughout this document.

The SI project elements were performed in compliance with Comprehensive Environmental 

Response, Compensation, and Liability Act (CERCLA; United States [US] 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 US Department of the Army (DA) requirements and guidance for field 

investigations.

1.2 SI Purpose

A PA was performed at the Waiawa Gulch Training Site and UTES (AECOM Technical Services, 

Inc. [AECOM], 2020) that identified two Areas of Interest (AOIs) where PFAS-containing materials 

may have been used, stored, disposed, or released historically. The objective of the SI is to 

identify whether there has been a release to the environment from the AOIs 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.

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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2. Facility Background

2.1 Facility Location and Description

The Waiawa Gulch Training Site and UTES facility is located north of Pearl Harbor, on the island 

of O‘ahu (Figure 2-1). The facility falls 0.75 miles northeast of the H1-H2 freeway merge. The 

facility is bordered to the north and south by industrial activities and to the west by a privatelyoperated junk yard. The Waiawa Gulch Training Site and UTES facility comprises approximately 

20 acres.

Prior to Hawai‘i ARNG (HIARNG) use, the UTES portion of the installation was owned and 

operated by the Navy as a military vehicle and equipment maintenance and storage facility from 

1943 to 1951. When Navy operations at the facility ended, the land was transferred to the US 

Army. HIARNG acquired Naval Aviation Supply Depot Waiawa Gulch from the US Army in 1961.

Waiawa Gulch Training Site and UTES facility provides training and maintenance for the various 

units that support the Hawaiʻi (HIARNG. The Waiawa Gulch Training Site and UTES facility 

consists of office areas, a wash bay, maintenance shop, motor pool, and various small storage 

buildings. Historical aerial photography indicates that a large motor pool and storage facility were

located on the northern portion of the property, prior to 2014. The US Navy historically had 

ownership of the facility property from 3 August 1945. On 21 July 1959, the property was 

transferred to the HIARNG (Argonne National Laboratory, 1993).

2.2 Facility Environmental Setting

The Waiawa Gulch Training Site and UTES facility is located approximately 1.25 miles north of 

Middle Loch (Pearl Harbor). Throughout Waiawa Gulch Training Site and UTES, the natural 

terrain slopes south towards Pearl Harbor and west towards Waiawa Stream, ranging from a 

maximum elevation of 90 feet above mean sea level (amsl) to 50 feet amsl (Figure 2-2).

2.2.1 Geology

Two major volcanic mountain ranges forming the island of O‘ahu are the Wai‘anae Range in the 

west and the much younger Ko‘olau Range in the east. Both ranges are the eroded remnants of 

the large elongate Wai‘anae and Ko‘olau shield volcanoes. After a long period of erosion, volcanic 

activity resumed with the Honolulu Volcanic Series and its eruption of vents and lava flows. The 

eruptions produced by these features tended to be discrete, explosive events that produced 

volumes of ash, which blanketed older sloping Ko‘olau basalt baserock. 

On the central and eastern side of O‘ahu, the underlying baserock extrusive volcanic layers are 

lava flows from the Ko‘olau shield volcano. Layers of  ́a ́ā flows, pāhoehoe flows, and clinker 

boundaries can be found in the subsurface (Macdonald et. al, 1983). Geology beneath the facility 

is older alluvium.

The facility lies predominately on soil consisting of fill materials originating from dredging or hauled 

in from nearby areas (Argonne National Laboratory, 1993), and alluvium. This soil is composed 

of primarily silty clay and sandy clay. The soil along the boundaries of the facility consists of 

Kawaihapai stony clay loam (Department of the Navy [DON], 2016). The total thickness of the soil 

formation decreases from north to south, with maximum depth to bedrock at 200 feet below 

ground surface (bgs) (DON, 1990). Figure 2-3 uses United State Geological Survey (USGS) data 

from the Geologic Map of the State of Hawai‘i to show local geologic units at the facility (USGS, 

2007).
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SI soil boring depths ranged from 24.25 to 56 feet bgs. The borings primarily consisted of lean 

clay and sandy silt with varying concentrations of gravel. Fat clay was reported in one boring 

(AOI01-02) at 5 to 10 feet bgs. Many of the logs also reported fill (described as sandy silt, lean 

clay, and well-graded sand) at the surface. At greater depths, weathered basalt and basalt rock 

flour were observed interbedded with the unconsolidated alluvial clayey and silty soils. The facility 

observations are consistent with the understood land fill material expected. Boring logs are 

presented in Appendix E.

2.2.2 Hydrogeology

In the Waiawa Valley, an aquifer formed in the alluvium is recharged by rainfall, flood waters from 

Waiawa Stream, and streambed leakage. The alluvial aquifer is approximately 100 to 200 feet 

thick. The upper zone of the Pearl Harbor Basal aquifer lies beneath the alluvial aquifer and is 

separated by a layer of saturated saprolite. The low permeability of the saprolite keeps the 

hydraulic heads of the two aquifers distinct; however, flow from alluvial aquifer groundwater to the 

upper zone of the basal aquifer may occur (DON, 1990). 

The Waiawa basal aquifer, which underlies the Waiawa Gulch Training Site and UTES and alluvial 

aquifer, is part of the Pearl Harbor Aquifer, the most productive aquifer in the state. The hydrologic 

and geologic classification of the Waiawa aquifer system (Hawai‘i Department of Health [HDOH] 

Aquifer Code 3-02-02-111, Status Code 11111) at the facility describes the aquifer as a basal, 

unconfined aquifer in horizontally extensive flank basalt lava flows. The basal groundwater 

originates as rainwater falling in higher drainage basins to the north and northeast of the facility. 

The basal groundwater generally migrates seaward towards Pearl Harbor through zones of 

clinkers (Macdonald et. al, 1983). The basal aquifer can be divided into three layers: upper, 

middle, and lower. The upper basal aquifer consists of a mixture of rainfall recharge, irrigation 

return, and subsurface inflow. The middle layer consists primarily of cooler subsurface inflow from 

mountain recharge areas, and the lower layer is slightly warmer than the middle layer (DON, 

1990). The groundwater status for the upper aquifer is classified as the following: a currently used 

drinking water source that is ecologically important; fresh water (salinity less than 250 milligrams 

per liter chloride); irreplaceable in uniqueness; and highly vulnerable to contamination (Mink and 

Lau, 1990). Local hydrogeological units are shown on Figure 2-3.

An Environmental Data Resources, Inc.TM (EDR)TM report conducted a well search for a 1-mile 

radius surrounding the facility, and additional online resources, such as state and local 

Geographic Information System databases, were used to research wells within a 4-mile radius of 

the facility. Numerous wells of various use exist in all directions, and multiple industrial, 

agricultural, irrigation, and domestic wells are located directly downgradient of the facility. Based 

on the position and depth of these wells, it is possible that some of the wells are screened in the 

alluvial aquifer. Municipal water supply wells are located both east and west of the facility, within 

4 miles (Figure 2-3). Based on the position and depths of the municipal water supply wells, they 

are screened in the basal aquifer. Drinking water at Waiawa Gulch Training Site and UTES is 

resourced from public drinking water wells that are located cross-gradient, approximately 0.65 

miles southeast of the facility. These are the Honolulu Board of Water Supply Pearl City Shaft, 

Pearl City 1, and Pearl City 2 wells, which range from 140 to 151 feet bgs (State of Hawai‘i 

Commission on Water Resource Management [CWRM], 2022). 

Depths to water measured in March 2022 during the SI ranged from 31.96 to 52.21 feet local 

mean sea level. SI borings were completed in the unconfined alluvial aquifer underlying the facility. 

Based on the predominant subsurface materials observed (lean clays and sandy silt), the borings 

did not reach the extensive flank basalt lava flows that characterize the basal aquifer. Because 

the basal aquifer depth at the facility is unknown, additional data are needed to evaluate the 

potential for a hydrogeologic connection between the groundwater encountered in the SI borings 

and the basal aquifer groundwater. 
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Groundwater elevations at AOI 1 were higher (44.32 to 52.21 feet local mean sea level) than 

groundwater elevations at AOI 2 (31.96 to 34.98 feet local mean sea level). The SI boring logs 

and drilling conditions indicate a complex hydrogeological setting at the facility. At AOI 1, the two 

monitoring wells were installed with well screens at similar elevations; however, based on the 

depths to groundwater observed, it is possible the wells are screened in discontinuous waterbearing units. Additionally, based on the boring logs for the permanent well installation at AOI01-

02, the well screen interval was set below the groundwater table. As a result, groundwater 

elevation contours are not shown on Figure 2-4 for the AOI 1 area. Permanent well AOI01-02 is 

included in the groundwater elevation contours shown to provide a comparison of elevation data 

between AOI 1 and AOI 2. Additional data are necessary to determine groundwater flow direction 

at AOI 1. The groundwater elevation at AOI01-02 compared to the groundwater elevations at AOI 

2 suggests groundwater flows southwest across the greater facility area, which follows the

presumed regional groundwater flow of the basal aquifer south towards Pearl Harbor.

Although groundwater across the facility presumably flows southwest, there is uncertainty 

surrounding groundwater flow based on the localized groundwater elevation observed at AOI 2 

during the SI. In the southern portion of the facility near AOI 2, groundwater elevations indicate a 

convergence of flow near AOI02-02. This may be due to heterogeneous subsurface materials, 

such as disconnected clay lenses, or the influence of underground stormwater channels. It is also 

possible that surface topography influences the convergence at this location, as surface 

topography indicates a local depression at that point. It is unknown whether Waiawa Stream 

affects groundwater flow at each AOI. Groundwater elevation contours from the SI are presented 

on Figure 2-4. Depth to groundwater and groundwater elevations are discussed further and 

tabulated in Sections 5.3 and 5.4.

2.2.3 Hydrology

The facility is located within the main Pearl Harbor Watershed, which encompasses 110 square 

miles and comprises nine subwatersheds. The facility lies within the Waiawa subwatershed, which 

consists of Waiawa Stream and its tributaries (Commander, Navy Region Hawai‘i, 2011). Waiawa 

Stream partially borders Waiawa Gulch Training Site and UTES along the southwestern boundary 

(Figure 2-5). Waiawa Stream drains south to Middle Loch, within Pearl Harbor, approximately 

1.25 miles away, and subsequently to the Pacific Ocean. Stormwater runoff at the facility is 

directed towards a series of storm drains and a drainage pit located in the southwest corner of 

the property, near the storage buildings. A dry-well system formerly existed at the facility but has 

been capped and is no longer functional. The drainage pit was constructed in 2019 and receives 

stormwater discharge from the wash rack. Facility storm drains ultimately discharge into Waiawa 

Stream.

2.2.4 Climate

O‘ahu is located in the tropics, with a climate characterized by mild temperatures, northeasterly 

trade winds year-round, and moderate humidity. Hawai‘i has two seasons: summer (between May 

and October) and winter (between October and April). The annual average temperature in nearby 

Wahiawa is 71.9 degrees Fahrenheit (°F), with temperatures decreasing at higher elevations. The 

coldest average temperatures are in January (68.5°F), and the warmest temperatures are in 

August (75.5°F) (National Oceanic and Atmospheric Administration [NOAA], 2022). Humidity on 

O‘ahu ranges from approximately 30 to 90 percent (%). Precipitation predominantly occurs when 

the island’s mountain masses capture and cool the rising, warm, moist ocean air, producing higher 

rainfall in the windward and mountain areas, and lower rainfall in the leeward and coastal zones. 

Annual rainfall ranges from 20 inches in the leeward coastal areas to 250 inches on the Ko‘olau 

mountain peaks (Macdonald et.al, 1983) Nearby Wahiawa has an average annual rainfall of 64.8

inches (NOAA, 2022).
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2.2.5 Current and Future Land Use

Current Waiawa Gulch Training Site and UTES operations include training and maintenance for 

the various units that support the HIARNG. In addition to vehicle maintenance and support for 

HIARNG, periodic training exercises and course work for the National Guard units are conducted 

at the facility. The facility is staffed by both full- and part-time employees. 

Portions of the northern and southern borders of Waiawa Gulch Training Site and UTES are 

abutted primarily by industrial land use. A junk yard abuts the northwestern boundary of the facility. 

Across the road of the eastern border is a small industrial park. The closest urban center is Pearl 

City, approximately 0.1 miles to east. 

Reasonably anticipated future land use is not expected to change from the current land use 

described above.

2.2.6 Sensitive Habitat and Threatened/ Endangered Species 

The following birds, mammals, and plants are federally endangered, threatened, proposed, and/ 

or are listed as candidate species for the facility area (US Fish and Wildlife Service [USFWS], 

2022).

• Birds: Band-rumped storm-petrel, Oceanodroma castro (endangered); Hawaiian 

Duck/Koloa, Anas wyvilliana (endangered); Hawaiian stilt, Himantopus mexicanus knudseni

(endangered); Hawaiian coot, Fulica americana alai (endangered); Hawai‘i ‘akepa, Loxops 

coccineus (endangered); Hawaiian common gallinule, Gallinula galeata sandvicensis 

(endangered); Newell's Townsend's shearwater, Puffinus auricularis newelli (threatened)

• Mammals: Hawaiian hoary bat, Lasiurus cinereus semotus (endangered)

• Flowering plants: ‘aiea, Nothocestrum latifolium (endangered); ‘akoko, Euphorbia 

celastroides var. kaenana (endangered); ‘akoko, Euphorbia kuwaleana (endangered); 

‘ena‘ana, Pseudognaphalium sandicensium var. molokaiense (endangered); Carter’s 

Panicgrass, Panicum fauriel var. carteri (endangered); ‘Ihi, Portalaca villosa (endangered); 

‘Ohai, Sesbania tomentosa (endangered); Pu‘uka‘a, Cyperus trachysanthos (endangered); 

Spermolepsis hawaiiensis (no common name, endangered); Vigna o-wahuensis (no 

common name, endangered)

• Ferns and Allies: Ihi‘ihi, Marsilea villosa (endangered)

2.3 History of PFAS Use

Two potential release areas were identified at the Waiawa Gulch Training Site and UTES during 

the PA where aqueous film-forming foam (AFFF) may have been used or released historically 

(AECOM, 2020). The Waiawa Gulch Training Site and UTES includes a Firetruck Pump Test Area 

as well as a Vehicle Maintenance Area, Firetruck Parking Area, and Storage Buildings potentially 

impacted by AFFF use or storage. The Firetruck Pump Test Area in the northern portion of the 

facility is a grassy area used for vehicle storage and for pump testing of a firetruck. Because there 

is little knowledge regarding historical pump testing activities, AFFF may have been released 

within the grassy area where testing occurred. The Firetruck Pump Test Area is considered AOI 

1. The southern portion of the facility includes the vehicle maintenance area and surrounding 

areas where AFFF was discharged from the facility firetruck in the early 2000s, the grassy firetruck 

parking area, and the storage buildings on the edge of the grassy area where AFFF has been 

stored. These areas comprise AOI 2. Descriptions of AOI 1 and AOI 2 are presented in Section 

3.
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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, four potential release areas were 

identified at Waiawa Gulch Training Site and UTES and grouped into two AOIs (AECOM, 2020).

The potential release areas are shown on Figure 3-1.

3.1 AOI 1 Firetruck Pump Test Area

AOI 1 is in the north portion of the facility. Because there is little knowledge regarding historical

pump testing activities, AFFF may have been released within the grassy area where testing 

occurs. AOI 1 is an open grassy area that is used for vehicle storage and for pump testing of the 

firetruck. According to interviews, the pumps on the truck were tested once a month by spraying 

water at a tree located within the northern portion of the facility. During the pump testing, the 

firetruck parked in the northern portion of the facility. The testing activities may have released 

AFFF into the grass and migrated via surface runoff to the adjacent Waiawa Stream. Stormwater 

runoff at AOI 1 is captured by storm drains that ultimately discharge into Waiawa Stream, which 

is located in the vicinity of the storage buildings. The Waiawa Stream flows south to Middle Loch, 

within Pearl Harbor, and subsequently the Pacific Ocean.

3.2 AOI 2 Vehicle Maintenance Area, Firetruck Parking Area, and 

Storage Buildings

AOI 2 is in the southern portion of the facility and includes the vehicle maintenance area and 

surrounding areas where AFFF was discharged from the facility firetruck in the early 2000s, the 

grassy firetruck parking area, and the storage buildings where AFFF has been stored. One 55-

gallon drum of 3% Ansulite AFFF and one 5-gallon pail of 6% 3M AFFF were originally located in 

the metal portable storage units located north of the maintenance building. Later, the drum and 

pail were moved to the right side of a future stone hazardous materials storage building. The drum 

and pail were transported in September 2020 for disposal at a mainland facility.

During interviews, it was confirmed that the firetruck was filled with 3% AFFF concentrate in the 

early 2000s, and an unknown quantity of foam was released in a large open area covered in 

asphalt between the vehicle maintenance buildings adjacent to Waihona Street. There are two 

storm drains located within the reported area of release that discharge to Waiawa Stream. One 

storm drain is located northwest of the release area, and the second is located southeast of the 

release area. Additionally, Tri-MaxTM units may have been serviced at the vehicle maintenance 

buildings by discharging a volume of foam from the extinguishers into plastic trash bags; however, 

this is uncertain based on interviews. The disposition of the bagged AFFF is unknown.

AFFF discharge and storage within AOI 2 may have resulted in releases to the paved and grassy 

areas at the firetruck parking area, vehicle maintenance buildings, and the storage buildings. 

AFFF released to the pavement may also have drained to storm drains that discharge to an outfall 

located along Waiawa Stream.

3.3 Adjacent Sources

No potential off-site sources of were identified during the PA; however, fires have been 

documented at the adjacent, privately owned junk yard. Facility staff noted that a large explosion 

historically occurred in the 1990s at the adjacent junk yard. The explosion caused items from 

within the junk yard to be projected over onto the Waiawa Gulch Training Site and UTES property. 
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According to interviewee’s knowledge of the associated firefighting efforts, the fires were put out 

with water. 
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4. Project Data Quality Objectives

As identified during the Data Quality Objective (DQO) process and outlined in the SI Quality 

Assurance Project Plan (QAPP) Addendum (AECOM, 2021), the objective of the SI is to identify 

whether there has been a release to the environment at the AOIs 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 at each of the sampled 

AOIs.

4.1 Problem Statement

ARNG will recommend an AOI for Remedial Investigation (RI) if related soil and/or groundwater 

samples have concentrations of the relevant compounds above the OSD risk-based SLs. The 

SLs are presented in Section 6.1 of this report.

4.2 Information Inputs

Primary information inputs included:

• The PA for Waiawa Gulch Training Site and UTES (AECOM, 2020);

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

with the site-specific Uniform Federal Policy (UFP)-QAPP Addendum (AECOM, 2021); and

• 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 by the property limits of the facility (Figure 2-2) with respect to soil 

and groundwater sampling. The scope of the SI was vertically bounded by the basal aquifer underlying 

the facility. All drilling was performed within the surficial unconsolidated aquifer, not the Pearl Harbor 

Aquifer. There is not much seasonable variability at the facility, thus temporal boundaries did not limit 

the scope of the SI. SI activities performed at the facility were conducted in March and April, and the 

results reflect conditions at the facility at that time. There was no severe weather event just before or 

during field activities. Additionally, off-facility sampling may be performed if drinking water wells are 

identified within 1.25 miles of the facility boundary in the southern direction. If the wells to the 

south are identified as drinking water wells, the proper stakeholders will be notified, and necessary 

rights-of-entry will be obtained by ARNG with property owner(s). The results of the off-facility 

potable well sampling will be reported in a separate memorandum. 

4.4 Analytical Approach

Samples were analyzed by Pace Analytical Gulf Coast, accredited under the Department of 

Defense (DoD) Environmental Laboratory Accreditation Program (ELAP; Accreditation Number 

74960) and the National Environmental Laboratory Accreditation Program (NELAP; Certificate

Number 01955). Data were compared to applicable SLs within this document and decision rules 

as defined in the SI QAPP Addendum (AECOM, 2021).

Discrete bulk soil samples were collected in the field and sent to the laboratory where they were

subsampled and prepared using incremental sample methodology (ISM), per the SI QAPP 

Addendum. Soil samples were not collected in the field using ISM. A subset of soil samples 
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collected were also incidentally prepared using standard preparation technique in addition to ISM 

preparation. When this error was discovered, these samples were reprepared via ISM. For the 

purpose of this report, the ISM preparation concentration data for those samples are used to 

evaluate sample locations and are provided on figures and tables. The standard preparation 

analysis concentration results for those samples is provided in Appendix F. Groundwater 

samples were collected via low-flow sampling ar newly installed permanent monitoring wells and 

submitted to the laboratory for analysis. Groundwater samples were not collected or prepared 

using ISM. 

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 decisionmaking (DoD, 2019a; DoD, 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 SI QAPP Addendum (AECOM, 2021). 
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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 implemented 

in accordance with the following approved documents:

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

(PQAPP) dated March 2018 (AECOM, 2018a);

• Final Programmatic Accident Prevention Plan dated July 2018 (AECOM, 2018b); 

• Final Preliminary Assessment Report, Waiawa Gulch Training Site and Unit Training and

Equipment Site, O’ahu, Hawai‘i dated September 2020 (AECOM, 2020);

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

Waiawa Gulch Training Site and Unit Training and Equipment Site, O’ahu, Hawai‘i dated 

November 2021 (AECOM, 2021); and

• Final Site Safety and Health Plan, Waiawa Gulch Training Site and Unit Training and 

Equipment Site, O’ahu, Hawai‘i dated March 2022 (AECOM, 2022).

The SI field activities were conducted from 18 March to 11 April 2022 and consisted of utility 

clearance, direct push boring, soil sample collection, permanent monitoring well installation via solid 

flight auger drilling, well development, groundwater sample collection, and land surveying. Field 

activities were conducted in accordance with the SI QAPP Addendum (AECOM, 2021), except as 

noted in Section 5.8.

The following samples were collected during the SI and analyzed for a subset of 18 compounds

by liquid chromatography with tandem mass spectrometry (LC/MS/MS) compliant with Quality 

Systems Manual (QSM) 5.3 Table B-15 to fulfill the project DQOs. Aqueous samples were 

analyzed via standard preparation; solid samples were analyzed via ISM preparation:

• Fifteen (15) soil samples from nine boring locations;

• Six groundwater samples from six permanent monitoring wells; 

• Nineteen (19) quality assurance (QA)/quality control (QC) 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 media. 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. Sampling forms are provided in Appendix B2, Field Change Requests are

provided in Appendix B3, and land survey data are provided in Appendix B4. 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 for each of these activities are presented below.

5.1.1 Technical Project Planning

The US Army Corps of Engineers (USACE) TPP Process, Engineer Manual (EM) 200-1-2 

(USACE, 2016) 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 
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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 20 July 2021, prior to SI field activities. The 

combined TPP Meeting 1 and 2 was conducted in general accordance with EM 200-1-2. The 

stakeholders for this SI include the ARNG, HIARNG, USACE, and HDOH. EA Engineering, 

Science, and Technology, Inc. (EA) participated in these meetings for informational purposes.

Stakeholders were provided the opportunity to make comments on the technical sampling 

approach and methods at the combined TPP Meeting 1 and 2. The outcome of the combined TPP 

Meeting 1 and 2 was memorialized in the SI QAPP Addendum (AECOM, 2021).

A TPP Meeting 3 will be held after the field event to discuss the results of the SI. Meeting minutes 

for TPP 3 will be included in Appendix D of this report. Future TPP meetings will provide an 

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

5.1.2 Utility Clearance

AECOM placed a ticket with the AT&T JHITS for cable toning to provide utility clearance and notify 

them of intrusive work on 15 March 2022. Additionally, AECOM contracted Ground Penetrating 

Radar Systems (GPRS), a private utility location service, to perform utility clearance. GPRS

performed utility clearance of the proposed boring locations on 18 March 2022 with input from the 

AECOM field team and facility staff. General locating services and ground-penetrating radar were 

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

a hand auger to verify utility clearance in shallow subsurface where utilities would typically be 

encountered.

5.1.3 Source Water and Sampling Equipment Acceptability

Two potable water sources at Waiawa Gulch Training Site and UTES were sampled on 9 August

2021 to assess usability for decontamination of drilling equipment. Results of the samples

collected (WU-DECON-01 and WU-DECON-02) confirmed the sources to be acceptable for use 

in this investigation; therefore, they were used throughout the field activities. A third sample was 

collected from the drillers tote tank used to contain the potable water from the decontamination 

water sources (WU-DECON-03). The results of the decontamination water sample collected from 

the drillers tote tank confirmed the tote water to be acceptable for use in the investigation as well. 

The samples were analyzed by LC/MS/MS compliant with QSM 5.3 Table B-15. The results of the 

decontamination water samples used during the SI are provided in Appendix F. A discussion of 

the results is presented in the DUA (Appendix A).

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

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

was provided in the Standard Operating Procedures (SOPs) appendix to the SI QAPP Addendum 

(AECOM, 2021). Prior to the start of field work each day, a Sampling Checklist was completed as 

an additional layer of control. The checklist served as a daily reminder to each field team member 

regarding the allowable materials within the sampling environment.

5.2 Soil Borings and Soil Sampling

Borings were installed by GeoTek Hawaiʻi, Inc., a Hawai‘i-licensed driller, under direction by 

AECOM. Borings were installed in grass areas where applicable, to avoid disturbing concrete or 

asphalt surfaces. One boring was installed through an asphalt surface (AOI02-01). Soil samples 

were collected via direct push technology (DPT), in accordance with the SI QAPP Addendum 

(AECOM, 2021). A GeoProbe® 7822DT dual-tube sampling system was used to collect continuous 
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soil cores to the target depth. A hand auger was used to collect soil from the top 5 feet of the 

boring, in accordance with AECOM utility clearance procedures. The soil boring locations are 

shown on Figure 5-1, and depths are provided Table 5-1. Several boring locations were adjusted 

within a 50-feet offset for reasons including drill rig access and utility avoidance. Soil boring 

location AOI02-04 was relocated approximately 57 feet to the northwest to avoid subsurface and 

overhead utilities, as described in Section 5.8.

In general, two discrete bulk soil samples (between 1 kilogram [kg] and 1.5 kg) were collected

from the vadose zone for chemical analysis from each soil boring where permanent monitoring 

wells were installed: one bulk surface soil sample (0 to 2 feet bgs), and one bulk subsurface soil 

sample from approximately 2 feet above the groundwater table extending down to the 

groundwater interface. Additionally, three locations where permanent monitoring wells were not 

installed were sampled for only bulk surface soil from 0 to 2 feet bgs. Bulk samples were collected 

from soil spanning the entire 2-foot interval identified from the hand auger or DPT liner and

submitted to the laboratory for incremental subsampling and analysis. Soil samples were not 

collected via ISM but were prepared at the laboratory via ISM. 

The soil cores were continuously logged for lithological descriptions by an AECOM field geologist 

using the Unified Soil Classification System (USCS). A photoionization detector (PID) was used 

to screen the breathing zone during boring activities as part of personal safety requirements. 

Observations and measurements were recorded on sampling forms (Appendix B2) and in a nontreated field logbook (i.e., composition notebook). Depth interval, recovery thickness, PID 

concentrations, moisture, relative density, color (using a Munsell soil color chart), and texture 

(using the USCS) were recorded. The boring logs are provided in Appendix E.

SI soil boring depths ranged from 24.25 to 56 feet bgs. The borings consisted primarily of lean 

clay and sandy silt with varying concentrations of gravel. Fat clay was reported in one boring 

(AOI01-02) at 5 to 10 feet bgs. Many of the logs also reported fill (sampled as sandy silt, lean 

clay, and well graded sand) at the surface. At greater depths, weathered basalt and basalt rock 

flour were observed interbedded with the unconsolidated alluvial clayey and silty soils.

Each soil sample was collected into laboratory-supplied PFAS-free plastic bags and labeled using 

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

(FedEx) under standard chain of custody (CoC) procedures to the laboratory and analyzed by 

LC/MS/MS compliant with QSM 5.3 Table B-15, total organic carbon (TOC) (USEPA Method 

9060A), and pH (USEPA Method 9045D) in accordance with the SI QAPP Addendum (AECOM, 

2021). Grain size analysis was not performed, in accordance with the SI QAPP Addendum, 

because discrete horizontal and vertical clay units were not encountered in the field (AECOM, 

2021). Clay layers were present across the facility.

Field duplicate samples were collected from the same borings as their parent samples at a rate 

of 10% and analyzed for the same parameters as the accompanying samples. Matrix spike 

(MS)/MS duplicates (MSDs) were collected from the same borings as their parent samples 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, equipment rinsate blanks were collected at a rate of 5% 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 (°C) during shipment.

DPT borings were converted to permanent monitoring wells in accordance with the SI QAPP 

Addendum (AECOM, 2021).
Site Inspection Report

Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i

AECOM 5-4

5.3 Permanent Well Installation and Groundwater Sampling

During the SI, six permanent monitoring wells were installed within or downgradient of potential

source areas. The locations of the wells are shown on Figure 5-1. 

A GeoProbe® 7822DT drill rig was used to install six 2-inch diameter monitoring wells into the 

unconfined alluvium underlying the facility; the wells were not installed into the basal aquifer. The 

monitoring wells were constructed with Schedule 40 PVC, flush threaded 10-foot sections of riser, 

0.010-inch slotted well screen, and a threaded bottom cap. A filter pack of Cemex clean, graded, 

kiln-dried, Monterey sand was installed in the annulus around the well screen to a minimum of 2

feet above the well screen. A seal was installed above the filter pack using hydrated 3/8 inch 

bentonite chip pellets, followed by hydrated bentonite installed in lifts to within two feet of the well 

pad, per the HDOH Hazard Evaluation and Emergency Response Office (HEER) Technical 

Guidance Manual (TGM) (HDOH, 2021). A Field Change Request describing the use of hydrated 

bentonite lifts instead of bentonite grout is included in Appendix B3. The hydrated bentonite was 

overlain with 2 feet of neat Portland cement. All monitoring wells were completed with flush mount 

well vaults and constructed with a concrete well pad. The screen interval of each groundwater 

monitoring well is provided in Table 5-2.

Development and sampling of wells was completed in accordance with the SI QAPP Addendum 

(AECOM, 2021). The newly installed monitoring wells were developed no sooner than 24 hours 

following installation by pumping and surging using a variable speed submersible pump. Samples 

were collected no sooner than 24 hours following development via low-flow sampling methods 

using a peristaltic pump or a QED Sample Pro® bladder pump with disposable PFAS-free, HDPE 

tubing. A peristaltic pump was used to sample the shallower wells at AOI 2; a bladder pump was 

used to sample the deeper wells at AOI 1. New tubing was used at each well, and the pumps 

were decontaminated between each well. The pump tubing, or pump itself when using a bladder 

pump, were placed at the center of the well screen during purging. The wells were purged at a 

rate determined in the field to minimize draw down during pre-sample purging, and during sample 

collection. Water quality parameters (e.g., temperature, specific conductance, pH, dissolved 

oxygen [DO], and oxidation-reduction potential [ORP]) were measured using a water quality meter 

and recorded on the field sampling form (Appendix B2). Purging was considered complete when 

three consecutive field parameter measurements of temperature, pH, specific conductivity, DO 

and ORP stabilized within approximately 10% and the turbidity was at or below 10 nephelometric 

turbidity units (NTU) or within ± 10% if above 10 NTU. Water levels were measured to the nearest 

0.01 inch and recorded. Additionally, a subsample of each groundwater sample was collected in 

a separate container, and a shaker test was completed to determine the presence or absence of 

foaming capability in the sample. No foaming was noted in any of the groundwater samples.

Each sample was collected into laboratory-supplied PFAS-free HDPE bottles 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 by LC/MS/MS compliant with QSM 5.3

Table B-15 in accordance with the SI QAPP Addendum (AECOM, 2021). Appendix G contains 

the CoCs by sample delivery group within the laboratory reports.

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. One field reagent blank was collected in 

accordance with the PQAPP (AECOM, 2018a). A temperature blank was placed in each cooler to 

ensure that samples were preserved at or below 6 °C during shipment.
Site Inspection Report

Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i

AECOM 5-5

5.4 Synoptic Water Level Measurements

A synoptic groundwater gauging event was performed on 6 April 2022. Groundwater elevation 

measurements were collected from the six new permanent monitoring wells. Water level 

measurements were taken from the northern side of the well casing. A groundwater flow contour 

map is provided in Figure 2-4. Groundwater elevation data are provided in Table 5-2.

5.5 Surveying

The northern side of each well casing was surveyed by Hawai‘i-licensed land surveyors following 

guidelines provided in the SI QAPP Addendum SOPs (AECOM, 2021). Survey data from the 

newly installed wells on the facility were collected on 11 April 2022 in the applicable World 

Geodetic System 1984 Universal Transverse Mercator Zone 4 datum (horizontal) as well as the 

North American Datum 1983 State Plane Hawai‘i Zone 3 (horizontal), and Hawai‘i’s Local Mean 

Sea Level datum (vertical). The surveyed well data are provided in Appendix B4.

5.6 Investigation-Derived Waste

As of the date of this report, the disposal of 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 SI QAPP Addendum (AECOM, 2021) and with the DA Guidance for 

Addressing Releases of PFAS, Q18 (DA, 2018).

All solid (i.e., soil cuttings) and liquid (i.e., purge water, development water, and decontamination 

fluids) IDW were contained in labeled, 55-gallon steel drums and left onsite in a waste storage 

area designated by HIARNG. ARNG will manage and dispose of the solid and liquid IDW under 

a separate contract in accordance with SOP No. 042A for Treating Liquid Investigation-Derived 

Material (Purge water, drilling water, and decontamination fluids) (EA, 2021). 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 as non-hazardous solid waste to be transported to a licensed solid waste landfill.

5.7 Laboratory Analytical Methods

Samples were analyzed by LC/MS/MS compliant with QSM 5.3 Table B-15 at Pace Analytical Gulf 

Coast in Baton Rouge, Louisiana, 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 SI QAPP Addendum

Two deviations from the SI QAPP Addendum were identified during SI field work. The deviation 

is noted below and is documented in Field Change Request Forms (Appendix B3): 

• During the pre-drilling utility clearance, one boring (AOI02-04) was relocated due to 

accessibility issues. The original location was within 10 feet of overhead power lines. The 

proposed drilling location was moved approximately 57 feet to the northwest to allow for 

safe drilling away from overhead power lines, subsurface utilities, and the newly installed 

facility wash rack infrastructure. This action was documented in a Field Change Request

provided in Appendix B3.

• During permanent monitoring well installation, the well construction details were revised. 

Based on the current HDOH HEER TGM and recommendation from the experienced, 

Hawai‘i-licensed driller, the use of slurry/grout seals is not recommended due to the potential 
Site Inspection Report

Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i

AECOM 5-6

for infiltration and clogging of the filter pack. The permanent wells were constructed with a 

seal above the sand filter pack using hydrated 3/8-inch bentonite chip pellets, followed by 

hydrated bentonite installed in lifts to prevent bridging instead of a bentonite grout, as 

described in the SI QAPP Addendum (AECOM, 2021). These actions were documented in 

a nonconformance report dated July 2022 and are provided in Appendix B3.
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, Waiawa UTES, Hawaiʻi

Sample Identification

Sample

Collection 

Date/Time

Sample Depth 

(feet bgs) LC/MS/MS compliant with QSM 5.3 Table B-15 (ISM Preparation) LC/MS/MS compliant with QSM 5.3 Table B-15 (Standard Preparation) TOC (USEPA Method 9060A) pH (USEPA Method 9045D) Comments

AOI01-01-SB-0-2 3/21/2022 10:45 0 - 2 x

AOI01-01-SB-0-2-D 3/21/2022 10:45 0 - 2 x FD

AOI01-01-SB-0-2-MS 3/21/2022 10:45 0 - 2 x MS

AOI01-01-SB-0-2-MSD 3/21/2022 10:45 0 - 2 x MSD

AOI01-01-SB-37-39 3/21/2022 9:45 37 - 39 x

AOI01-02-SB-0-1 3/28/2022 9:00 0 - 1 x x x x

AOI01-02-SB-0-1-D 3/28/2022 9:10 0 - 1 x x FD

AOI01-02-SB-25.5-27.5 3/28/2022 11:05 25.5 - 27.5 x x

AOI02-01-SB-0-2 3/24/2022 13:40 0 - 2 x x

AOI02-01-SB-14.5-16.5 3/24/2022 14:10 14.5 - 16.5 x x x x

AOI02-01-SB-14.5-16.5-D 3/24/2022 14:30 14.5 - 16.5 x x FD

AOI02-01-SB-14.5-16.5-MS 3/24/2022 14:25 14.5 - 16.5 x x MS

AOI02-01-SB-14.5-16.5-MSD 3/24/2022 14:25 14.5 - 16.5 x x MSD

AOI02-02-SB-0-2 3/23/2022 9:40 0 - 2 x

AOI02-02-SB-14-16 3/23/2022 11:50 14 - 16 x

AOI02-03-SB-0-2 3/24/2021 9:35 0 - 2 x x

AOI02-03-SB-16.5-18.5 3/24/2022 10:05 16.5 - 18.5 x x

AOI02-04-SB-0-2 3/23/2022 14:30 0 - 2 x

AOI02-04-SB-14-16 3/23/2022 15:55 14 - 16 x

AOI02-05-SB-0.0-0.5 3/29/2022 13:50 0 - 0.5 x x

AOI02-06-SB-0.0-0.5 3/29/2022 14:00 0 - 0.5 x x

AOI02-07-SB-0-2 3/29/2022 14:10 0 - 2 x x

AOI01-01-GW 4/5/2022 12:30 NA x

AOI01-02-GW 4/5/2022 13:35 NA x

AOI02-01-GW 4/4/2022 15:45 NA x

AOI02-01-GW-D 4/4/2022 15:45 NA x FD

AOI02-01-GW-MS 4/4/2022 15:45 NA x MS

AOI02-01-GW-MSD 4/4/2022 15:45 NA x MSD

AOI02-02-GW 4/5/2022 8:30 NA x

AOI02-03-GW 4/5/2022 14:55 NA x

AOI02-04-GW 4/5/2022 15:45 NA x

Soil Samples

Groundwater Samples

AECOM 5-7
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, Waiawa UTES, Hawaiʻi

Sample Identification

Sample

Collection 

Date/Time

Sample Depth 

(feet bgs) LC/MS/MS compliant with QSM 5.3 Table B-15 (ISM Preparation) LC/MS/MS compliant with QSM 5.3 Table B-15 (Standard Preparation) TOC (USEPA Method 9060A) pH (USEPA Method 9045D) Comments

WU-ERB-01 3/21/2022 12:00 NA x Hand Auger

WU-ERB-03 3/28/2022 11:20 NA x Hand Trowel

WU-ERB-04 3/28/2022 15:00 NA x Macrocore Shoe

WU-ERB-05 3/28/2022 15:05 NA x DT32 Drill Tooling

WU-ERB-06 3/28/2022 15:30 NA x Solid Flight Auger Shoe

WU-ERB-07 4/5/2022 17:00 NA x Development Pump

WU-ERB-08 4/6/2022 10:00 NA x Water Level Meter

WU-Decon-01 8/9/2021 8:55 NA x Decontamination Water Source

WU-Decon-02 8/9/2021 9:15 NA x Decontamination Water Source

WU-Decon-03 3/29/2022 9:45 NA x Driller Water Tank

WU-FRB-01 3/21/2022 13:30 NA x Lab-provided Sand

WU-FRB-02 4/1/2022 10:45 NA x Lab-provided Water

Notes:

ASTM = American Society for Testing and Materials

bgs = below ground surface

ERB = equipment rinsate blank

FD = field duplicate

FRB = field reagent blank

LC/MS/MS = Liquid Chromatography Mass Spectrometry

MS/MSD = matrix spike/ matrix spike duplicate

QSM = Quality Systems Manual

TOC = total organic carbon

USEPA = United States Environmental Protection Agency

Quality Control Samples

AECOM 5-8
Table 5-2

Soil Boring Depths, Monitoring Well Screen Intervals, and Groundwater Elevations

Site Inspection Report, Waiawa UTES, Hawaiʻi

Area of 

Interest

Boring 

Location

Soil Boring 

Depth 

(feet bgs)

Monitoring Well 

Screen Interval 

(feet bgs)1

Top of Casing 

Elevation 

(local mean sea 

level)

Ground Surface 

Elevation 

(local mean sea 

level)

Depth to 

Water

(feet btoc)

Depth to 

Water

(feet bgs)

Groundwater 

Elevation

(local mean sea 

level)

AOI01-01 56 45 - 55 89.40 89.70 45.08 45.39 44.32

AOI01-02 48 37 - 47 83.13 83.50 30.92 31.28 52.21

AOI02-01 25.25 15 - 25 48.86 49.13 15.8 16.08 33.06

AOI02-02 25.25 15 - 25 49.61 49.98 17.65 18.02 31.96

AOI02-03 25.25 15 - 25 50.35 50.75 17.21 17.61 33.14

AOI02-04 24.25 14 - 24 50.40 50.76 15.42 15.78 34.98

AOI02-05 0.5 NA NA 48.21 NA NA NA

AOI02-06 0.5 NA NA 48.67 NA NA NA

AOI02-07 2 NA NA 48.55 NA NA NA

Notes:

1

 Well screen set above total depth to capture groundwater interface

bgs = below ground surface

btoc = below top of casing

NA = not applicable

1

2

AECOM 5-9
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AECOM 

Site Inspection ReportWaiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i 
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Site Inspection Sample Locations

Base Map: Source: Esri, Maxar, Earthstar Geographics,

and the GIS User Community

PROJECT Site Inspection at Waiawa Gulch Training Site and UTES, HI

?! Soil Boring/Monitoring Well Location

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Area of Interest

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Groundwater Flow Direction

Groundwater elevations in ft NAVD88.

* Excluded from contouring.

1:3,240 ­

0 135 270 540

Feet

AECOM 5-11
Site Inspection Report

Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i 

AECOM 5-12

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Site Inspection Report

Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i 

AECOM 6-1

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 each AOI is provided in Section 6.3 and 

Section 6.4. Table 6-2 through Table 6-5 present results in 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 on Table 

6-1 below.

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

Analyteb

Residential

(Soil)

(μg/kg)a 

0-2 feet bgs

Industrial/ 

Commercial 

Composite 

Worker

(Soil)

(μg/kg)a 

2-15 feet bgs

Tap Water

(Groundwater)

(ng/L)a

PFOA 19 250 6 

PFOS 13 160 4

PFBS 1,900 25,000 601 

PFHxS 130 1,600 39

PFNA 19 250 6 

Notes:

bgs = below ground surface; μg/kg = micrograms per kilogram; ng/L = nanograms per liter

a.) Assistant Secretary of Defense, 2022. Risk Based Screening Levels in Groundwater and Soil using United States Environmental Protection 

Agency’s (USEPA’s) Regional Screening Level Calculator. Hazard Quotient (HQ) = 0.1. 6 July 2022. 

b.) 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 HFPODA 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. 

The data in the subsequent sections are compared to 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 feet bgs) 

and the industrial/commercial worker scenario is applied to shallow subsurface soil results (2 to 

15 feet bgs). The SLs are not applied to deep subsurface soil results (>15 feet bgs) because 15 

feet is the anticipated limit of construction activities. 
Site Inspection Report

Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i

AECOM 6-2

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. Grain size analysis was not performed, in accordance with the SI 

QAPP Addendum, because discrete horizontal and vertical clay units were not encountered in the 

field (AECOM,2021).

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 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).

6.3 AOI 1

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

1: Firetruck Pump Test Area. The soil and groundwater results are summarized on Table 6-2

through Table 6-5. Soil and groundwater results are presented on Figure 6-1 through Figure 6-

7.

6.3.1 AOI 1 Soil Analytical Results

Figure 6-1 through Figure 6-5 present the ranges of detections in soil. Table 6-2 through Table 

6-4 summarize the soil results.

Surface soil was sampled from 0 to 2 feet bgs and deep subsurface soil collected from 25.5 to 39 

feet bgs at boring locations AOI01-01 and AOI01-02. PFOS, PFHxS, and PFNA were detected in 

surface soil samples at concentrations less than 1.73 J (estimated concentration) micrograms per 

kilogram (μg/kg); all detected concentrations were below the SLs in surface soil. PFOA and PFBS 

were not detected in surface soil. In the deep subsurface soil, PFOS and PFHxS were detected 

at one location, AOI01-02 (25.5 to 27.5 feet bgs), with concentrations of 0.524 J μg/kg and 0.325

J μg/kg, respectively. PFOA, PFBS, and PFNA were not detected in deep subsurface soil.

6.3.2 AOI 1 Groundwater Analytical Results

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

summarizes the groundwater results.

Groundwater was sampled from permanent monitoring wells AOI01-01 and AOI01-02. The 

following exceedances of the SLs were measured:

• PFOA was detected above the SL of 6 nanograms per liter (ng/L) at AOI01-02, with a 

concentration of 18.0 ng/L. 

• PFOS was detected above the SL of 4 ng/L at AOI01-02, with a concentration of 11.1 

ng/L. 

• PFHxS was detected above the SL of 39 ng/L at AOI01-02, with a concentration of 89.3

ng/L. 
Site Inspection Report

Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i

AECOM 6-3

PFBS and PFNA were detected below their SLs at AOI01-02. PFOA and PFOS were detected 

below their SLs at AOI01-01; PFBS, PFHxS, and PFNA were not detected at AOI01-01.

6.3.3 AOI 1 Conclusions

Based on the results of the SI, PFOS, PFHxS, and PFNA were detected in soil below their SLs.

PFOA, PFOS, and PFHxS were detected in groundwater at concentrations above their SLs. 

Based on detections in soil and exceedances of the SLs in groundwater, further evaluation at AOI 

1 is warranted.

6.4 AOI 2

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

AOI 2: Vehicle Maintenance Area, Firetruck Parking Area, and Storage Buildings. The results in 

soil and groundwater are summarized on Table 6-2 through Table 6-5. Soil and groundwater 

results are presented on Figure 6-1 through Figure 6-7.

6.4.1 AOI 2 Soil Analytical Results

Figure 6-1 through Figure 6-5 present the ranges of detections in soil. Table 6-2 through Table 

6-4 summarize the soil results.

Surface soil was sampled from 0 to 2 feet bgs at boring locations AOI02-01 through AOI02-07. 

Soil was also sampled from the shallow subsurface (14 to 16.5 feet bgs) at boring locations AOI02-

01, AOI02-02, and AOI02-04; and deeper subsurface (16.5 to 18.5 feet bgs) from boring location 

AOI02-03.

PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in soil at concentrations less than 2.50

J+ (estimated concentration, biased high) μg/kg and below their SLs in surface soil.

PFOS, PFHxS, and PFNA were detected in shallow subsurface soil, at concentrations less than 

0.387 J μg/kg; all detected concentrations were below the SLs in shallow subsurface soil. PFOA 

and PFBS were not detected in shallow subsurface soil.

In deep subsurface soil, PFOS and PFHxS were detected at concentrations of 0.125 J μg/kg and 

0.076 J μg/kg, respectively; PFOA, PFBS, and PFNA were not detected. 

6.4.2 AOI 2 Groundwater Analytical Results

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

summarizes the groundwater results.

Groundwater was sampled from permanent monitoring wells AOI2-01 through AOI02-04. The 

following exceedances of the SLs were measured:

• PFOA was detected above the SL of 6 ng/L in all four wells, with concentrations ranging 

from 13.3 ng/L to 57.0 ng/L. 

• PFOS was detected above the SL of 4 ng/L in all four wells, with concentrations ranging 

from 31.2 ng/L to 271 ng/L. 

• PFHxS was detected above the SL of 39 ng/L in all four wells, with concentrations

ranging from 39.7 ng/L to 1,110 ng/L. 

PFBS and PFNA were detected below their SLs in all four wells. 
Site Inspection Report

Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i

AECOM 6-4

6.4.3 AOI 2 Conclusions

Based on the results of the SI, PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in soil at 

concentrations below their respective SLs. PFOA, PFOS, and PFHxS were detected in 

groundwater at concentrations above their SLs. Based on detections in soil and exceedances of 

the SLs in groundwater, further evaluation at AOI 2 is warranted.
Table 6-2

PFOA, PFOS, PFBS, PFNA, and PFHxS ISM Results in Surface Soil

Site Inspection Report, Waiawa Gulch Training Site and UTES

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual 

PFBS 1900 ND UJ ND UJ ND UJ ND UJ 0.046 J ND UJ ND UJ 0.023 J NPFHxS 130 0.050 J 0.042 J ND UJ 0.032 J 1.41 J ND UJ ND UJ 0.054 J 0.

PFNA 19 0.053 J 0.056 J 0.081 J 0.100 J ND UJ 0.736 J 0.049 J 0.046 J 0.PFOA 19 ND UJ ND UJ ND UJ ND UJ ND UJ 0.271 J ND UJ 0.127 J 0.PFOS 13 1.73 J 1.65 J 0.547 J 0.675 J 2.48 J 0.735 J 0.223 J 0.498 J 2.

Notes Chemical AbbreviationsGrey Fill Detected concentration exceeded OSD Screening Levels PFBS perfluorobutanesulfonic acidND = Analyte not detected above the LOD PFHxS perfluorohexanesulfonic acid

LOD values are presented in Appendix F. PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

References PFOS perfluorooctanesulfonic acid

Acronyms and AbbreviationsAOI Area of InterestD duplicate

Interpreted Qualifiers DL detection limitJ = Estimated concentration ft feet

J+ = Estimated concentration, biased high HQ hazard quotient

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

ISM Incremental Sampling MethodoLCMSMS liquid chromatography with tandLOD limit of detectionND analyte not detected above the OSD Office of the Secretary of DefenQSM Quality Systems ManualQual interpreted qualifierSB soil boringUSEPA United States Environmental PrUTES Unit Training and Equipment Siμg/kg micrograms per kilogram

Area of Interest

Sample ID

Sample Date

Depth

AOI01-01-SB-0.0-2.0

03/21/2022

0-2 ft

AOI01

AOI01-01-SB-0.0-2.0-D

03/21/2022

0-2 ft

AOI01-02-SB-0.0-1.0

03/28/2022

0-1 ft

AOI01-02-SB-0.0-1.0-D

03/28/2022

AOI02

03/23/2022

0-2 ft

AOI02-03-SB-0.0-2.0

03/24/2022

0-2 ft

a. Assistant Secretary of Defense, July 2022. Risk Based Screening Levels Calculated for PFOA, PFOS, PFBS, PFHxS, and PFNA in Groundwater or Soil using USEPA’s Regional Screening Level Calculator. HQ=0.1, May 2022. Soil screening levels based on residential scenario for incidental ingestion of contaminated soil.

Soil, LCMSMS compliant with QSM 5.3 Table B-15 (μg/kg)

AOI02-04-SB-0.0-2.0

03/23/2022

0-2 ft

A

AOI02-02-SB-0.0-2.0

0-1 ft

AOI02-01-SB-0.0-2.0

03/24/2022

0-2 ft

AECOM 
Table 6-2

PFOA, PFOS, PFBS, PFNA, and PFHxS ISM Results in Surface Soil

Site Inspection Report, Waiawa Gulch Training Site and UTES

Analyte OSD Screening 

Level a

Result Qual

PFBS 1900 ND UJPFHxS 130 ND UJPFNA 19 0.068 JPFOA 19 0.099 JPFOS 13 0.455 J

Notes Chemical AbbreviationsGrey Fill Detected concentration exceeded OSD Screening Levels PFBS perfluorobutanesulfonic acid

ND = Analyte not detected above the LOD PFHxS perfluorohexanesulfonic acid

LOD values are presented in Appendix F. PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

References PFOS perfluorooctanesulfonic acid

Acronyms and AbbreviationsAOI Area of InterestD duplicate

Interpreted Qualifiers DL detection limitJ = Estimated concentration ft feet

J+ = Estimated concentration, biased high HQ hazard quotient

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

ISM Incremental Sampling MethodologyLCMSMS liquid chromatography with tandem mLOD limit of detectionND analyte not detected above the LODOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierSB soil boringUSEPA United States Environmental ProtectioUTES Unit Training and Equipment Siteμg/kg micrograms per kilogram

Soil, LCMSMS compliant with QSM 5.3 Table B-15 (μg/kg)

a. Assistant Secretary of Defense, July 2022. Risk Based Screening Levels Calculated for PFOA, PFOS, PFBS, PFHxS, and PFNA in Groundwater or Soil using USEPA’s Regional Screening Level Calculator. HQ=0.1, May 2022. Soil screening levels based on residential scenario for incidental ingestion of contaminated soil.

Area of Interest

Sample ID

Sample Date

Depth

AOI02

AOI02-07-SB-0.0-2.0

03/29/2022

0-2 ft

AECOM 
Table 6-3

PFOA, PFOS, PFBS, PFNA, and PFHxS ISM Results in Shallow Subsurface Soil

Site Inspection Report, Waiawa Gulch Training Site and UTES

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual

PFBS 25000 ND UJ ND UJ ND UJPFHxS 1600 ND UJ 0.065 J 0.387 J

PFNA 250 0.021 J 0.032 J ND UJPFOA 250 ND UJ ND UJ ND UJPFOS 160 0.132 J 0.162 J ND UJ

Notes Chemical AbbreviationsGrey Fill Detected concentration exceeded OSD Screening Levels PFBS perfluorobutanesulfonic acid

ND = Analyte not detected above the LOD PFHxS perfluorohexanesulfonic acidLOD values are presented in Appendix F. PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

References PFOS perfluorooctanesulfonic acid

Acronyms and AbbreviationsAOI Area of InterestDL detection limit

Interpreted Qualifiers ft feetJ = Estimated concentration HQ hazard quotientUJ = The analyte was not detected at a level greater than or equal to the adjusted DL. However, the reported adjusted DL is approximate and may be inaccurate or imprecise. ID identification

ISM Incremental Sampling MethoLCMSMS liquid chromatography with tLOD limit of detectionND analyte not detected above tOSD Office of the Secretary of DeQSM Quality Systems ManualQual interpreted qualifierSB soil boringUSEPA United States EnvironmentaUTES Unit Training and Equipmenμg/kg micrograms per kilogram

Soil, LCMSMS compliant with QSM 5.3 Table B-15 (μg/kg)

a. Assistant Secretary of Defense, July 2022. Risk Based Screening Levels Calculated for PFOA, PFOS, PFBS, PFHxS, and PFNA in Groundwater or Soil using USEPA’s Regional Screening Level Calculator. HQ=0.1, May 2022. Soil screening levels based on industrial/commercial composite worker scenario for incidental ingestion of contaminated soil.

AOI02

AOI02-02-SB-14.0-16.0

03/23/2022

14-16 ft

AOI02-04-SB-14.0-16.0

03/23/2022

14-16 ft

Area of Interest

Sample ID

Sample Date

Depth

AOI02-01-SB-14.5-16.5

03/24/2022

14.5-16.5 ft

AECOM 
Table 6-4

PFOA, PFOS, PFBS, PFNA, and PFHxS ISM Results in Deep Subsurface Soil

Site Inspection Report, Waiawa Gulch Training Site and UTES

Area of Interest

Sample ID

Sample Date

Depth

Analyte Result Qual Result Qual Result Qual

PFBS ND UJ ND UJ ND UJPFHxS ND UJ 0.325 J 0.076 JPFNA ND UJ ND UJ ND UJPFOA ND UJ ND UJ ND UJPFOS ND UJ 0.524 J 0.125 J

Notes Chemical AbbreviationsND = Analyte not detected above the LOD PFBS perfluorobutanesulfonic acidLOD values are presented in Appendix F. PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

Interpreted Qualifiers PFOA perfluorooctanoic acid

J = Estimated concentration PFOS perfluorooctanesulfonic acidUJ = The analyte was not detected at a level greater than or equal to the adjusted DL. However, the reported adjusted DL is approximate and may be inaccurate or imprecise.

Acronyms and Abbreviations

AOI Area of InterestDL detection limitft feetID identificationISM Incremental Sampling MethodologLCMSMS liquid chromatography with tandeLOD limit of detectionND analyte not detected above the LOQSM Quality Systems ManualQual interpreted qualifierSB soil boringUTES Unit Training and Equipment Siteμg/kg micrograms per kilogram

AOI02

AOI02-03-SB-16.5-18.5

03/24/2022

16.5-18.5 ft

Soil, LCMSMS compliant with QSM 5.3 Table B-15 (μg/kg)

AOI01

AOI01-01-SB-37.0-39.0

03/22/2022

37-39 ft

AOI01

AOI01-02-SB-25.5-27.5

03/28/2022

25.5-27.5 ft

AECOM 
Table 6-5

PFOA, PFOS, PFBS, PFNA, and PFHxS Results in Groundwater

Site Inspection Report, Waiawa Gulch Training Site and UTES

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual

PFBS 601 ND U 13.7 8.00 8.66 56.2 125 12.5

PFHxS 39 ND U 89.3 39.7 40.6 1110 409 459

PFNA 6 ND U 1.97 J 2.71 J 2.68 J 5.44 1.32 J 1.01 JPFOA 6 1.26 J 18.0 13.3 13.7 57.0 27.9 25.3

PFOS 4 2.64 J 11.1 31.4 31.2 271 212 71.2

Notes Chemical AbbreviationsGrey Fill Detected concentration exceeded OSD Screening Levels PFBS perfluorobutanesulfonic acid

ND = Analyte not detected above the LOD PFHxS perfluorohexanesulfonic acid

LOD values are presented in Appendix F. PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

References PFOS perfluorooctanesulfonic acid

Acronyms and Abbreviations

AOI Area of InterestD duplicate

Interpreted Qualifiers DL detection limitJ = Estimated concentration GW groundwater

U = The analyte was not detected at a level greater than or equal to the adjusted DL HQ hazard quotient

ID identificationLCMSMS liquid chromatography with tandem mLOD limit of detectionND analyte not detected above the LODOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierUSEPA United States Environmental ProtectioUTES Unit Training and Equipment Siteng/l nanogram per liter

Water, LCMSMS compliant with QSM 5.3 Table B-15 (ng/l)

a. Assistant Secretary of Defense, July 2022. Risk Based Screening Levels Calculated for PFOA, PFOS, PFBS, PFHxS, and PFNA in Groundwater or Soil using USEPA’s Regional Screening Level Calculator. HQ=0.1, May 2022 Groundwater screening levels based on residential scenario for direct ingestion of groundwater.

AOI01 AOI02

AOI02-03-GW

04/05/2022

AOI02-04-GW

04/05/2022

AOI02-01-GW-D

04/04/2022

AOI02-02-GW

04/05/2022

AOI01-02-GW

04/05/2022

AOI02-01-GW

04/04/2022

Area of Interest

Sample ID

Sample Date

AOI01-01-GW

04/05/2022

AECOM 
THIS PAGE INTENTIONALLY BLANK

AECOM 

Site Inspection ReportWaiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i 
AOI01-01

AOI02-01

AOI02-02

AOI02-03

AOI02-04

AOI02-05

AOI02-07

AOI01-02

AOI02-06

Waiawa Stream

Waiawa Stream

Facility Boundary

River/Stream

Trench Drain Figure 6-1

CLIENT

REVISED

SCALE

ARNG

Site Inspection at Waiawa Gulch Training Site and UTES, HI

1/26/2023

1/26/2023

1/26/2023

MS

JW

CM

GIS BY

CHK BY

PM

Base Map: Source: Esri, Maxar, Earthstar Geographics, and the GIS User Community

1/26/2023

PFOA Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

PROJECT

1:3,240 ­

Waiawa Stream

Waiawa Stream

AOI01-01

AOI02-01

AOI02-02

AOI02-03

AOI02-04

AOI01-02

Shallow Deep

Exceedances of the OSD SL are depicted with a yellow halo.

Depth intervals shown represent respective sampling position within a given soil boring location.

0 135 270 540

Feet

PFOA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

AECOM 6-11
AOI01-01

AOI02-01

AOI02-02

AOI02-03

AOI02-04

AOI02-05

AOI02-06

AOI02-07

AOI01-02

Waiawa Stream

Waiawa Stream

Facility Boundary

River/Stream

Trench Drain Figure 6-2

CLIENT

REVISED

SCALE

ARNG

Site Inspection at Waiawa Gulch Training Site and UTES, HI

1/26/2023

1/26/2023

1/26/2023

MS

JW

CM

GIS BY

CHK BY

PM

Base Map: Source: Esri, Maxar, Earthstar Geographics, and the GIS User Community

1/26/2023

PFOS Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

PROJECT

1:3,240 ­

Waiawa Stream

Waiawa Stream

AOI01-01

AOI02-01

AOI02-02

AOI02-03

AOI02-04

AOI01-02

Shallow Deep

Exceedances of the OSD SL are depicted with a yellow halo.

Depth intervals shown represent respective sampling position within a given soil boring location.

0 135 270 540

Feet

PFOS Results (μg/Kg)

ND

>ND - 13

>13 - 160

>160 - 1,600

>1,600

AECOM 6-12
AOI01-01

AOI02-01

AOI02-02

AOI02-03

AOI02-04 AOI02-05

AOI02-06

AOI02-07

AOI01-02

Waiawa Stream

Waiawa Stream

Facility Boundary

River/Stream

Trench Drain Figure 6-3

CLIENT

REVISED

SCALE

ARNG

Site Inspection at Waiawa Gulch Training Site and UTES, HI

1/26/2023

1/26/2023

1/26/2023

MS

JW

CM

GIS BY

CHK BY

PM

Base Map: Source: Esri, Maxar, Earthstar Geographics, and the GIS User Community

1/26/2023

PFBS Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

PROJECT

1:3,240 ­

Waiawa Stream

Waiawa Stream

AOI01-01

AOI02-01

AOI02-02

AOI02-03

AOI02-04

AOI01-02

Shallow Deep

Exceedances of the OSD SL are depicted with a yellow halo.

Depth intervals shown represent respective sampling position within a given soil boring location.

0 135 270 540

Feet

PFBS Results (μg/Kg)

ND

>ND - 10

>10 - 1,900

>1,900 - 25,000

>25,000

AECOM 6-13
AOI01-01

AOI02-01

AOI02-02

AOI02-03

AOI02-04

AOI02-05

AOI02-06

AOI02-07

AOI01-02

Waiawa Stream

Waiawa Stream

Facility Boundary

River/Stream

Trench Drain Figure 6-4

CLIENT

REVISED

SCALE

ARNG

Site Inspection at Waiawa Gulch Training Site and UTES, HI

1/26/2023

1/26/2023

1/26/2023

MS

JW

CM

GIS BY

CHK BY

PM

Base Map: Source: Esri, Maxar, Earthstar Geographics, and the GIS User Community

1/26/2023

PFHxS Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

PROJECT

1:3,240 ­

Waiawa Stream

Waiawa Stream

AOI01-01

AOI02-01

AOI02-02

AOI02-03

AOI02-04

AOI01-02

Shallow Deep

Exceedances of the OSD SL are depicted with a yellow halo.

Depth intervals shown represent respective sampling position within a given soil boring location.

0 135 270 540

Feet

PFHxS Results (μg/Kg)

ND

>ND - 10

>10 - 130

>130 - 1,600

>1,600

AECOM 6-14
AOI01-01

AOI02-01

AOI02-02

AOI02-03

AOI02-04 AOI02-05

AOI02-07

AOI01-02

AOI02-06

Waiawa Stream

Waiawa Stream

Facility Boundary

River/Stream

Trench Drain Figure 6-5

CLIENT

REVISED

SCALE

ARNG

Site Inspection at Waiawa Gulch Training Site and UTES, HI

1/26/2023

1/26/2023

1/26/2023

MS

JW

CM

GIS BY

CHK BY

PM

Base Map: Source: Esri, Maxar, Earthstar Geographics, and the GIS User Community

1/26/2023

PFNA Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

PROJECT

1:3,240 ­

Waiawa Stream

Waiawa Stream

AOI01-01

AOI02-01

AOI02-02

AOI02-03

AOI02-04

AOI01-02

Shallow Deep

Exceedances of the OSD SL are depicted with a yellow halo.

Depth intervals shown represent respective sampling position within a given soil boring location.

0 135 270 540

Feet

PFNA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

AECOM 6-15
Waiawa Stream

AOI01-01

AOI02-01

AOI02-02

AOI02-03

AOI02-04

AOI01-02

Facility Boundary

River/Stream

Trench Drain

Groundwater Flow Direction Figure 6-6

CLIENT

REVISED

SCALE

ARNG

Site Inspection at Waiawa Gulch Training Site and UTES, HI

1/26/2023

1/26/2023

1/26/2023

MS

JW

CM

GIS BY

CHK BY

PM

Base Map: Source: Esri, Maxar, Earthstar Geographics, and the GIS User Community

1/26/2023

PFOA, PFOS, and PFBS Detections in Groundwater

12420 Milestone Center Drive

Germantown, MD 20876

PROJECT

1:3,240 ­

Waiawa Stream

AOI01-01

AOI02-01

AOI02-02

AOI02-03

AOI02-04

AOI01-02

Waiawa Stream

AOI01-01

AOI02-01

AOI02-02

AOI02-03

AOI02-04

AOI01-02

PFOA PFOS PFBS

Exceedances of the OSD SL are depicted with a yellow halo.

0 135 270 540

Feet

PFOA Results (ng/L)

ND

>ND - 6

>6 - 40

>40 - 70

>70

PFOS Results (ng/L)

ND

>ND - 4

>4 - 40

>40 - 70

>70

PFBS Results (ng/L)

ND

>ND - 100

>100 - 601

>601 - 2,000

>2,000

AECOM 6-16
Waiawa Stream

Waiawa Stream

AOI01-01

AOI02-01

AOI02-02

AOI02-03

AOI02-04

AOI01-02

Facility Boundary

River/Stream

Trench Drain

Groundwater Flow Direction Figure 6-7

CLIENT

REVISED

SCALE

ARNG

Site Inspection at Waiawa Gulch Training Site and UTES, HI

1/26/2023

1/26/2023

1/26/2023

MS

JW

CM

GIS BY

CHK BY

PM

Base Map: Source: Esri, Maxar, Earthstar Geographics, and the GIS User Community

1/26/2023

PFHxS and PFNA Detections in Groundwater

12420 Milestone Center Drive

Germantown, MD 20876

PROJECT

1:3,240 ­

Waiawa Stream

Waiawa Stream

AOI01-01

AOI02-01

AOI02-02

AOI02-03

AOI02-04

AOI01-02

PFHxS PFNA

Exceedances of the OSD SL are depicted with a yellow halo.

0 135 270 540

Feet

PFNA Results (ng/L)

ND

>ND - 6

>6 - 100

>100 - 1,000

>1,000

PFHxS Results (ng/L)

ND

>ND - 39

>39 - 100

>100 - 1,000

>1,000

AECOM 6-17
THIS PAGE INTENTIONALLY BLANK

AECOM 6-18

Site Inspection Report

Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i 
Site Inspection Report

Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i

AECOM 7-1

7. Exposure Pathways

The conceptual site model (CSM) for the AOIs, 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; and

5. Potentially exposed populations.

If any of these elements are missing, the pathway is incomplete. The CSM figures use an empty 

circle symbol to represent an incomplete exposure pathway. Areas with an incomplete 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 (PFOA, PFOS, PFBS, PFHxS, and PFNA) 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 CSMs indicate 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 site workers (e.g., facility staff and visiting soldiers), construction 

workers, trespassers (though unlikely due to restricted access), residents outside the facility 

boundary, and recreational users outside of the facility boundary.

7.1 Soil Exposure Pathway

The SI results in soil were used to determine whether a potentially complete pathway exists 

between the source and potential receptors at AOI 1 and AOI 2 based on the aforementioned 

criteria.

7.1.1 AOI 1

AOI 1 is the grassy area in the north portion of the facility, where historical firetruck parking and 

pump testing activities may have resulted in the release of AFFF.

PFOS, PFHxS, and PFNA were detected below their SLs in surface soil at AOI 1. Site workers,

future construction workers, and trespassers could contact constituents in surface soil via 
Site Inspection Report

Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i

AECOM 7-2

incidental ingestion and inhalation of dust. Therefore, the surface soil exposure pathway for site 

workers, future construction workers, and trespassers are potentially complete. There was no 

active construction observed at AOI 1 during SI field work. PFOS and PFHxS were detected in 

subsurface soil at AOI 1. Construction workers could contact constituents in subsurface soil via 

incidental ingestion; therefore, the subsurface soil exposure pathway for future construction 

workers is potentially complete. The CSM for AOI 1 is presented on Figure 7-1. 

7.1.2 AOI 2

AOI 2 is in the southern portion of the facility and includes the vehicle maintenance area and 

surrounding areas where AFFF was discharged from the facility firetruck in the early 2000s, the 

grassy firetruck parking area, and the storage buildings on the edge of the grassy area where 

AFFF has been stored. AFFF discharge and storage within AOI 2 may have resulted in releases

to grassy areas at the firetruck parking area, vehicle maintenance area, and the storage buildings.

PFOA, PFOS, PFBS, PFHxS, and PFNA were detected below their SLs in surface soil at AOI 2. 

Site workers and construction workers could contact constituents in surface soil via incidental 

ingestion and inhalation of dust. Therefore, the surface soil exposure pathway for site workers,

future construction workers, and trespassers are potentially complete. There was no active 

construction observed at AOI 2 during SI field work. PFOS, PFHxS, and PFNA were detected in 

subsurface soil at AOI 2; therefore, the subsurface soil exposure pathway for future construction 

workers is potentially complete. The CSM for AOI 2 is presented on Figure 7-1. 

7.2 Groundwater Exposure Pathway

The SI results in groundwater were used to determine whether a potentially complete pathway 

exists between the source and potential receptors based on the aforementioned criteria.

7.2.1 AOI 1

PFOA, PFOS, and PFHxS were detected above their SLs in groundwater samples collected at 

AOI 1. Groundwater elevations across the facility indicate groundwater from AOI 1 flows south 

following the flow of the basal aquifer south towards Pearl Harbor. Domestic, agricultural, and 

irrigation wells are present in the southern, downgradient direction within 4 miles of the facility; 

however, most of these wells are set in the basal aquifer at depths greater than 75 feet bgs (State 

of Hawaiʻi CWRM, 2022). At least one well is listed as being set in the alluvial aquifer. Although 

the groundwater samples collected during this SI were collected from shallow wells set in the 

alluvium, it is conservatively assumed that the pathway for exposure to off-facility residents via 

ingestion of groundwater is potentially complete. Because the Waiawa Gulch Training Site and 

UTES facility is provided drinking water from municipal wells that range in depth from 140 to 151

feet bgs and are cross-gradient to the southeast of the facility, the pathway for exposure to site 

workers via ingestion of groundwater is considered incomplete. Depths to water measured at AOI 

1 in April 2022 during the SI ranged from 31.28 to 45.39 feet bgs. Therefore, the ingestion 

exposure pathway for future construction workers is considered incomplete. The CSM for AOI 1

is presented on Figure 7-1. 

7.2.2 AOI 2

PFOA, PFOS, and PFHxS were detected above their SLs in groundwater samples collected at 

AOI 2. Although groundwater elevations at AOI 2 indicate a convergence on AOI02-02, it is 

presumed that the prevailing flow of groundwater from AOI 2 is to the south. This presumption is 

based on the groundwater elevations observed at each AOI and the understood flow direction of 

the regional basal aquifer. For the same reasons described in Section 7.2.1, the pathway for 

exposure to off-facility residents via ingestion of groundwater is considered potentially complete, 
Site Inspection Report

Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i

AECOM 7-3

and the pathway for exposure to site workers, future construction workers, and trespassers via 

ingestion of groundwater is considered incomplete. Depths to water measured at AOI 2 in April 

2022 during the SI ranged from 15.78 to 18.02 feet bgs. Therefore, the ingestion exposure 

pathway for future construction workers is considered incomplete. The CSM for AOI 2 is presented 

on Figure 7-1. 

7.3 Surface Water and Sediment Exposure Pathway

The SI results in soil and groundwater, in combination with knowledge of the fate and transport 

properties of PFAS, were used to determine whether a potentially complete pathway exists 

between the source and potential receptors.

7.3.1 AOI 1

PFAS are water soluble and can migrate readily from soil to surface water via leaching and runoff. Because PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in soil and/or groundwater 

at AOI 1, it is possible that those compounds may have migrated from soil to storm drains in the 

area that capture runoff. Stormwater runoff at AOI 1 discharges into Waiawa Stream, which is 

located in the vicinity of the storage buildings. The Waiawa Stream flows south to Middle Loch, 

within Pearl Harbor, and subsequently the Pacific Ocean. Therefore, the surface water and 

sediment ingestion exposure pathway for recreational users of those surface water bodies is 

considered potentially complete. There is no surface water or sediment on the Waiawa Gulch 

Training Site and UTES property. As a result, the surface water and sediment ingestion exposure 

pathway for site workers, construction workers, and trespassers is considered incomplete.

Municipal drinking water is not supplied by nearby surface water bodies, such as Waiawa Stream. 

Consequently, the residential exposure pathway is incomplete for surface water and sediment 

ingestion. The OSD SLs for soil and groundwater are based on human receptors. Future surface 

water and sediment sampling may be performed to evaluate potential impacts to ecological 

receptors. 

7.3.2 AOI 2

Because PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in soil and/or groundwater at 

AOI 2, it is possible that those compounds may have migrated from soil to storm drains in the 

area that capture runoff. Storm drains discharge to an outfall located along Waiawa Stream. For 

the same reasons described in Section 7.3.1, the surface water and sediment ingestion exposure 

pathway for recreational users of downgradient surface water bodies is considered potentially 

complete; and the pathway for exposure pathway for site workers, construction workers, and 

trespassers is considered incomplete. Municipal drinking water is not supplied by nearby surface 

water bodies, such as Waiawa Stream. Consequently, the residential exposure pathway is 

incomplete for surface water and sediment ingestion. The OSD SLs for soil and groundwater are

based on human receptors. Future surface water and sediment sampling may be performed to 

evaluate potential impacts to ecological receptors.
Site Inspection Report

Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i

AECOM 7-4

THIS PAGE INTENTIONALLY BLANK
SOURCE PATHWAY RECEPTOR

AOI 1 & AOI 2

Firetruck pump 

testing, Tri-MaxTM

maintenance, and 

AFFF storage

Human 

Activities

Precipitation/ 

Run-Off

Leaching/ 

Infiltration

Airborne Soil 

Particulate

Surface Soil 

at AOI

Surface 

Water/ 

Sediment

Subsurface 

Soil

Shallow 

Groundwater

Source Release 

Mechanism Media Transport and Migration Media Exposure Routes

Inhalation of 

Dust

Ingestion

Ingestion

Ingestion

Ingestion

Human Receptors: 

Current/ Future

Flow-Chart Continues

Partial / Possible Flow

Flow-Chart Stops

Incomplete Pathway

Potentially Complete Pathway

Site Worker

Site Worker Construction Worker3 Resident1,2 Trespasser/ Recreational User1

/ /

/ / /

LEGEND

/

Figure 7-1

Conceptual Site Model, AOI 1 and AOI 2

Waiawa Gulch Training Site and UTES, HI

/

/

/

/

Surface Soil

/ / /

/ /

/

/ /

/ /

1. The resident and recreational users refer to offsite receptors.

2. Inhalation of dust for off-site receptors is likely

insignificant.

3. No current active construction at the facility.

Notes:

Potentially Complete Pathway 

with Exceedance of SL for PFOA, 

PFOS, PFBS, PFHxS, and/or 

PFNA

Construction Worker3 Resident1,2 Trespasser/ Recreational User1

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

7-5
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Site Inspection ReportWaiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i 

7-4

AECOM 
Site Inspection Report

Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i

AECOM 8-1

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 SI Activities

The SI field activities were conducted from 18 March to 11 April 2022 and consisted of utility 

clearance, direct push boring, soil sample collection, permanent monitoring well installation via solid 

flight auger drilling, well development, groundwater sample collection, and land surveying. Field 

activities were conducted in accordance with the SI QAPP Addendum (AECOM, 2021), except as 

previously noted in Section 5.8. 

To fulfill the project DQOs set forth in the approved SI QAPP Addendum (AECOM, 2021), samples 

were collected and analyzed for a subset of 18 compounds by LC/MS/MS compliant with QSM 5.3 

Table B-15 as follows. 

• Fifteen (15) soil samples from nine boring locations; 

• Six groundwater samples from six permanent monitoring wells; 

• Nineteen (19) quality assurance QA/QC 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 CSM was 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 is warranted in an RI for AOI 1: Firetruck Pump 

Test Area and AOI 2: Vehicle Maintenance Area, Firetruck Parking Area, and Storage Buildings. 

Based on the CSMs developed and revised in light of the SI findings, there is potential for 

exposure to drinking water receptors from AOI 1 and AOI 2 from sources on the facility resulting 

from historical DoD activities. Sample analytical concentrations collected during the SI were 

compared to the project SLs in soil and groundwater, as described in Table 6-1. A summary of 

the results of the SI data relative to the SLs is as follows:

• At AOI 1:

• The detected concentrations of PFOS, PFHxS, and PFNA in soil at AOI 1 were below 

their SLs. 

• PFOA, PFOS, and PFHxS in groundwater exceeded their SLs. PFOA exceeded the 

SL of 6 ng/L, with a concentration of 18.0 ng/L at location AOI01-02. PFOS exceeded

the SL of 4 ng/L, with a concentration of 11.1 ng/L at location AOI01-02. PFHxS 

exceeded the SL of 39 ng/L, with a concentration of 89.3 ng/L at location AOI01-02. 

Based on the results of the SI, further evaluation of AOI 1 is warranted in the RI.
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Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i 

AECOM 8-2

• At AOI 2: 

• The detected concentrations of PFOA, PFOS, PFBS, PFHxS, and PFNA in soil at 

AOI 2 were below their SLs. 

• PFOA, PFOS, and PFHxS in groundwater exceeded their SLs. PFOA exceeded the 

SL of 6 ng/L at all four locations, with a maximum concentration of 57.0 ng/L at 

location AOI02-02. PFOS exceeded the SL of 4 ng/L at all four locations, with a 

maximum concentration of 271 ng/L at location AOI02-02. PFHxS exceeded the SL 

of 39 ng/L at all four locations, with a maximum concentration of 1,110 ng/L at location 

AOI02-02. Based on the results of the SI, further evaluation of AOI 2 is warranted in 

an RI.

Due to the complex hydrogeologic setting encountered at the facility, there is uncertainty 

regarding local groundwater flow direction at AOI 1 and AOI 2. It is possible that wells within AOI 

1 are screened in discontinuous water-bearing units, and the influence of the nearby Waiawa 

Stream on groundwater flow is unknown. A future RI will provide additional data to clarify the 

hydrogeology. 

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 

Release Area

Soil –

Source Area

Groundwater –

Source Area Future Action

1 Firetruck Pump Test Area Proceed to RI 

2 Firetruck Parking Area, Vehicle 

Maintenance Area, and Storage Buildings Proceed to RI 

Legend:

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected
Site Inspection Report

Waiawa Gulch Training Site and Unit Training and Equipment Site, O‘ahu, Hawai‘i 

AECOM 9-1

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