FINAL

Site Inspection Report 

Gowen Field Army Aviation 

Support Facility 

Boise, Idaho

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....................................................................... 2-3

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

3.2 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 ..................................................................................... 4-1

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 Grab Sampling .............................. 5-3

5.4 Synoptic Water Level Measurements ..................................................................... 5-4

5.5 Surveying................................................................................................................ 5-4

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

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

5.8 Deviations from SI QAPP Addendum ..................................................................... 5-5

6. Site Inspection Results................................................................................................... 6-1

6.1 Screening Levels .................................................................................................... 6-1

6.2 Soil Physicochemical Analyses............................................................................... 6-1

6.3 AOI 1....................................................................................................................... 6-2

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

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

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

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

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

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

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

7.3 Surface Water and Sediment Exposure Pathway................................................... 7-2

7.3.1 AOI 1 ............................................................................................................ 7-2

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. Field Change Request Forms

B4. 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, November 2021

Figure 2-5 Surface Water Features

Figure 3-1 Area 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

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 Well Screen Intervals

Table 5-3 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

AASF Army Aviation Support Facility

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 

DA Department of the Army

DoD Department of Defense

DO dissolved oxygen

DQO data quality objective

DUA data usability assessment

EDRTM Environmental Data Resources, Inc.TM

ELAP Environmental Laboratory Accreditation Program

EM Engineer Manual

ERB equipment rinsate blank

FedEx Federal Express

FRB field reagent blank

FTA Fire Training Area

GPS Global positioning system

GPRS Ground Penetrating Radar Systems

HDPE high-density polyethylene 

HFPO-DA hexafluoropropylene oxide dimer acid

IDANG Idaho Air National Guard

IDARNG Idaho Army National Guard

IDW investigation-derived waste

IDWR Idaho Department of Water Resources

ITRC Interstate Technology Regulatory Council

LC/MS/MS liquid chromatography with tandem mass spectrometry

MIL-SPEC military specification

ND non-detect

NELAP National Environmental Laboratory Accreditation Program

ng/L nanograms per liter

ORP oxidation-reduction potential

OSD Office of the Secretary of Defense

PA Preliminary Assessment
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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

SI Site Inspection

SL screening level

SOP standard operating procedure

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
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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 three Areas of Interest (AOIs) where PFAS-containing materials may have been 

used, stored, disposed, or released historically. However, based on subsequent discussions with 

ARNG following the completion of the PA, it was determined that only AOI 1 (see Table ES-2) will 

be assessed under this SI. AOI 2 and AOI 3 are being assessed by IDANG under a separate SI 

and are considered to be adjacent sources under this SI. The objective of the SI is to identify 

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

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

immediate threats, or no further action is required based on SLs for relevant compounds. This SI 

was completed at Gowen Field AASF in Boise, Idaho and determined further evaluation under 

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

warranted for AOI 1. The Gowen Field AASF will also be referred to as the “facility” throughout 

this document. 

The Boise Airport is located in Ada County, within the boundary of the city of Boise, in western 

Idaho. In 1941, the facility was constructed for use as an air base and named Gowen Field, which 

remained an active Army Air Corps Base during WWII. The IDANG and the Idaho ARNG 

(IDARNG) are located on separate parcels within the former Gowen Field. The IDARNG property 

at Gowen Field AASF consists of approximately 240 acres and is located adjacent to the Boise 

Airport and IDANG property. The IDARNG facility consists mostly of operations and support 

buildings, as well as an AASF (Idaho National Guard, 2019). 

The PA identified three AOIs for investigation during the SI phase although two of these are being 

studied by IDANG. SI sampling results from AOI 1 evaluated during this SI were compared to 

OSD SLs. Table ES-2 summarizes the SI results for AOI 1. Based on the results of this SI, further 

evaluation under CERCLA is warranted in a Remedial Investigation (RI) for AOI 1. 

1

 Of the six PFAS compounds presented in the 6 July 2022 OSD memorandum, HFPO-DA (commonly referred to as GenX) was not 

included as an analyte at the time of this SI. Based on the conceptual site model (CSM) developed during the PA and revised based 

on SI findings, the presence of HFPO-DA is not anticipated at the facility because HFPO-DA is generally not a component of military 

specification (MIL-SPEC) aqueous film forming foam (AFFF) and based on its history including distribution limitations that restricted 

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

individual chemical of concern in the absence of other PFAS. 
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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 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 ES-2: Summary of Site Inspection Findings and Recommendations

AOI

Potential 

Release 

Area

Soil – 

Source Area

Groundwater – 

Source Area

Groundwater –

Facility 

Boundary

Future Action

1 AASF 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 Gowen Field AASF in 

Boise, Idaho. Gowen Field AASF is also 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 Gowen Field AASF (AECOM Technical Services, Inc. [AECOM], 2019) 

that identified three Areas of Interest (AOIs) where PFAS-containing materials may have been 

used, stored, disposed, or released historically: AOI 1: the Army Aviation Support Facility (AASF), 

AOI 2: the Central Drainage Ditch, and AOI 3: Idaho Air National Guard (IDANG) AFFF Dump 1. 

AOIs 2 and 3 are being assessed by IDANG under a separate SI and are consequently considered 

to be adjacent sources under this SI. The objective of the SI is to identify whether there has been 

a release to the environment from AOI 1 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 Boise Airport is located in Ada County within the boundary of the city of Boise, in western 

Idaho (Figure 2-1). The Gowen Field AASF property is leased from the city of Boise by the Idaho 

ARNG (IDARNG) and the IDANG. The Army Reserves, Navy Reserves, and Marine Reserves 

are IDARNG tenants. The IDANG-managed portion of Gowen Field AASF is directly adjacent to 

the IDARNG facility.

Construction of the facility began at Boise Air Base in 1941. Later that year, the facility was named 

Gowen Field, which remained an active Army Air Corps Base during World War II. After the end 

of the war, Gowen Field was turned back over to the city of Boise in 1946. The IDANG was 

established concurrently with the US Air Force in 1947 and moved to Gowen Field shortly after.

The IDARNG was a tenant under the IDANG's lease until 2013, when a separate lease with the 

city of Boise was established. The IDARNG currently occupies approximately 240 acres on the 

southwestern portion of Gowen Field AASF (Idaho National Guard, 2019).

2.2 Facility Environmental Setting

Gowen Field AASF is in the Boise River Valley, on a generally flat plot of land with an average 

elevation of about 2,800 feet above mean sea level (amsl) (Figure 2-2). Mountains to the south 

and north of the facility rise up to elevations of 8,500 feet amsl. The Boise River is to the north 

and northeast of the facility, at distances varying between 3.5 and 4 miles. The Snake River is to 

the southwest of the facility, at distances greater than 20 miles.

2.2.1 Geology

Gowen Field AASF is located in the Boise River Valley, within the broader Western Snake River 

Plain, just south of the foothills of the mountainous terrain of central Idaho. The Western Snake 

River Plain is a fault-bounded, intracontinental rift basin (Wood & Clemens, 2002). The Pliocene 

and Pleistocene geologic history of the Boise Valley includes crustal rifting, basin filling, river 

incision, eruptions of lava flows, and major flooding.

The Chalk Hills Formation constitutes the earliest sedimentation in the basin, characterized by a 

succession of fluvio-lacustrine sediments resulting from interconnected lakes, meandering 

streams, and lacustrine delta deposits. These lake levels declined and resulted in erosion of part 

of the Chalk Hills Formation in the Boise area. A subsequent rise in lake level led to the deposition 

of another lacustrine sequence, which includes shoreline sands, small deltas, and lacustrine mud 

in the deeper parts of the basin. These deposits are mapped as the Terteling Springs Formation 

(Wood & Clemens, 2002).

Spillover of this ancient lake system resulted in a slow lowering of the lake level and filling of the 

shrinking lake basins with interbedded mud and sand of lacustrine delta systems of the Glenns 

Ferry Formation (Wood & Clemens, 2002). In more recent geologic history, terraces were formed 

by rapid fluvial downcutting followed by coarse gravel deposition (Othberg, 1994). Gowen Field

AASF sits above these Pleistocene-age terrace gravel deposits (Figure 2-3), which consist of 

unconsolidated silt, sand, and well-sorted gravel beds characterized by cut-and-fill channels, 

inclined bedding, and cross-bedding.

Soil borings were completed at depths of 50 feet below ground surface (bgs) (two borings) and 

220 feet bgs (one boring) during the SI at Gowen Field AASF. Borings found well-graded gravel 

with sand as the dominant lithology of the unconsolidated sediments to 50 feet bgs. Well-graded 
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sand with silt was found as the dominant lithology from 50 to 220 feet bgs. Intermittent isolated 

layers of silt, gravel, and poorly graded silty sand were also observed in the deeper boring. These 

observations are consistent with the understood fluvial depositional environment. Boring logs are 

presented in Appendix E. 

2.2.2 Hydrogeology

Groundwater beneath the facility has been reported to range from as shallow as 120 feet bgs to 

depths greater than 200 feet bgs. The facility is currently supplied potable water by Suez Water 

Idaho, Inc. (Suez), a local provider, although some wells on-site were reported as being used for 

irrigation. The facility has used both shallow and deep aquifers for its water supply in the past.

The aquifer system in the Boise area consists of complex series of interbedded, tilted, faulted, 

and eroded sediments extending to depths of over 6,000 feet bgs. These sedimentary aquifers 

contain shallow, local flow systems, and a deeper, regional groundwater system (Petrich, 2004). 

Aquifer units are not well-defined in the region due to discontinuities and the lack of consistently 

identifiable contacts between units. Generally, highest groundwater production is from discrete 

sand aquifers located within the fluvial-lacustrine deposits within the upper 800 feet of the aquifer.

Within the Boise area, multiple wells have tapped into a deep aquifer (at 660 feet bgs). These 

wells are capable of yielding 180 to 1,400 gallons per minute (gpm). Suez wells are located 

approximately 2 miles north of the facility and have a 9.1-million-gallons-per-day capacity (Leidos, 

2014). Several wells listed for domestic use are located 2-3 miles to the north of and 1-3 miles to 

the east of the facility (Figure 2-3). Many wells of unknown use are located around the facility, 

within a 1-mile buffer (Idaho Department of Water Resources [IDWR], 2019). It is possible that 

some of these wells are used for potable purposes. Suez Water Idaho owns and operates an outof-use domestic water well at the former Gowen Field (Byrd Well), located approximately 2,700 ft 

upgradient from the former Fire Training Area (FTA). Byrd Well has reportedly not been used since 

2005. An additional off-Base well (Mac Well), owned and operated by Suez Water Idaho, is 

reportedly active and located approximately 4,000 ft west of the western boundary of the former 

Gowen Field (Leidos, 2019).

Results of groundwater characterization and modeling in this area show that the deeper aquifer 

flows south toward the Snake River (Petrich, 2004; Petrich & Urban, 2004). This work indicates 

downward vertical hydraulic gradients in the study area and suggests that recharge to the deep 

aquifer occurs primarily in the eastern portion of the Boise River Valley, where parts of the Idaho 

Group are exposed at the earth’s surface and ultimately discharge into major rivers. The study 

also indicated horizontal hydraulic conductivity ranging between 1 to 10 feet per day (ft/day) (from 

0 to 200 feet bgs), 10 to 100 ft/day (from 200 to 400 feet bgs), and 100 to 1,000 ft/day (from 400 

to 1200 feet bgs). In the area of Gowen Field, discharge to the Snake River drives the deep 

groundwater flow direction to the southwest. No portion of the recharge zone for the deep aquifer 

is coincident with Gowen Field.

Recharge to the shallow groundwater systems in the Boise River Valley occurs primarily from 

seepage from the canals and infiltration, mostly associated with irrigation. This creates variable 

shallow groundwater flow directions across the Boise River valley (Petrich & Urban, 2004). A 

groundwater study performed in the late 20th century of various locations in the southern portion 

of Gowen Field indicated that shallow groundwater flow within the immediate vicinity of the AASF 

is to the northeast. Groundwater elevations recorded during a 2018 PFOS/PFOA SI conducted 

by IDANG at Gowen Field ANG identified a general easterly groundwater flow. Furthermore, the 

SI indicated that south of Gowen Field AASF, groundwater flows toward the northeast. However, 

the SI found that immediately north of Gowen Field AASF, the groundwater flow direction appears 

to shift toward the east (Figure 2-3). The 2018 PFOS/PFOA SI indicated that deep groundwater 
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was encountered (Leidos, 2019); however, the easterly and variable flow direction appears 

consistent with the shallow aquifer.

Depths to groundwater were measured in the new monitoring well installed under this SI 

(GOWEN-MW001) along with seven existing Air National Guard (ANG monitoring wells, including 

MW-1-PRL01, RIMW-2, MW-3-PRL01, RIMW-4, MW-5-PRL01, MW-BOI10-01, and MW-BOI11-

01 (Figure 2-4). A synoptic depth to groundwater gauging event was conducted on 12 November 

2021, and depths to water ranged from 163.71 to 206.77 feet below top of casing. Groundwater 

elevation contours from the SI are presented on Figure 2-4 and indicate groundwater flow 

direction is to the northeast in the southwestern part of the facility before flowing to the southeast 

direction in the northeastern part of the facility. Hydraulic gradient values measured 0.0051 

feet/foot between MW-BOI11 and the 2,650-foot contour in the southwest, while measuring 

0.0012 feet/foot between MW-BOI05 and MW-BOI10 in the northeast. The groundwater flow 

directions appear consistent with the findings of the 2018 PFOS/PFOA SI conducted by IDANG. 

Additionally, the groundwater depths and flow direction may have been affected due to clustered 

IDANG well data, irrigation recharge, and nearby pumping wells.

2.2.3 Hydrology

Gowen Field AASF is located within the Boise River drainage basin, a semi-arid area that annually 

receives 11.84 inches of precipitation (National Oceanic and Atmospheric Administration [NOAA], 

2020). Surface drainage at Gowen Field AASF is controlled both by the local surface topography 

and a system of drainage ditches. The most important drainage ditch, the Central Drainage Ditch,

generally traverses the facility, with flow from east to west. This drainage ditch originates as the 

remnant of an intermittent stream on the adjacent IDANG property before traversing the IDARNG 

property and discharging to an off-facility retention pond, a stormwater control feature that 

maintains a semi-permanent pool of water (Figure 2-5). The retention pond is not owned by the 

IDARNG.

Fivemile Creek, an intermittent stream that flows only during periods of heavy rainfall or snowmelt 

runoff, runs parallel to and south of West Gowen Road. The creek originates in the mountains, 

approximately 3 miles away, and discharges into the New York Canal, approximately 1 mile 

downstream of the property. This canal eventually discharges into the Boise River, which is used 

for crop irrigation (Leidos, 2014). None of these surface water features are used for drinking water 

in Boise. 

2.2.4 Climate

Gowen Field AASF is located within Ada County, Idaho, which has a semi-arid climate with hot 

and dry summers and moderately cold winters. The average annual temperature is 53.5 degrees 

Fahrenheit (°F), ranging from an average winter low of 26.3 °F to an average summer high of 

89.1 °F. The mean annual precipitation in Boise is approximately 11.73 inches, with most of the 

precipitation occurring from November through May each year (NOAA, 2020). Gowen Field AASF 

averages over 39 days with more than 0.1 inches of precipitation. Ada County only receives an 

annual snowfall average of 12.48 inches (Leidos, 2019).

2.2.5 Current and Future Land Use

Currently, the IDARNG property at Gowen Field AASF consists of approximately 240 acres and 

is located adjacent to the Boise Airport and IDANG property. The IDARNG facility consists mostly 

of operations and support buildings, as well as an AASF; access to the facility is controlled. Land 

surrounding the facility to the north, east, and west is used for industrial purposes and airport 

operations. Land to the south of the facility is used for agricultural purposes and livestock grazing. 
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Residential areas are not located immediately adjacent to the facility. The closest residential areas 

are located approximately 0.75 miles to the north of the northern edge of the facility. 

Gowen Field AASF is located entirely within Ada County, within the city of Boise, Idaho. Based on 

official 2017 estimates from the US Census Bureau, Boise’s population is 226,570, and it is the 

largest city in Idaho (US Census Bureau, 2017). The IDARNG has been operating at Gowen Field 

AASF since 1946, and land use is not expected to change in the future.

2.2.6 Sensitive Habitat and Threatened/ Endangered Species 

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

of habitat. The following species have not been identified at the facility but may be present in the 

surrounding area. 

The following birds, plants, mammals, and reptiles are federally endangered, threatened, 

proposed, and/ or are listed as candidate species in Ada County, Idaho (US Fish and Wildlife 

Service [USFWS], 2021). 

• Insects: Monarch butterfly, Danaus plexippus (candidate)

• Mammals: Gray wolf, Canis lupus (under review)

• Birds: Yellow-billed cuckoo, Coccyzus americanus (threatened); Greater sage-grouse, 

Centrocercus urophasianus (resolved taxon)

• Snails: Snake River physa snail, Physa natricina (endangered)

• Flowering plants: Slickspot peppergrass, Lepidium papilliferum (threatened)

2.3 History of PFAS Use 

PFAS-containing materials were potentially released to soil, sediment, and groundwater within 

the boundary of Gowen Field AASF through nozzle testing and fuel spill response between 2005 

and 2015. Three AOIs were identified during the PA based on preliminary data and assumed 

groundwater flow directions. These AOIs included the AASF (AOI 1), the Central Drainage Ditch 

(AOI 2), and IDANG AFFF Dump 1 (AOI 3). However, based on subsequent discussions with 

ARNG following the completion of the PA, it was determined that only AOI 1 will be assessed 

under this SI. AOI 2 and AOI 3 are being assessed by IDANG under a separate SI and are 

considered to be adjacent sources under this SI. Therefore, only AOI 1 is presented in Section 

3. 
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Gowen Field AASF, Boise, Idaho

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Gowen Field AASF, Boise, Idaho

AECOM 3-1

3. Summary of Areas of Interest 

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

disposed, or released historically. Three potential PFAS release areas, the AASF, the Central 

Drainage Ditch, and IDANG AFFF Dump 1, were identified at Gowen Field AASF and grouped 

into three AOIs (AECOM, 2019). This SI Report assesses AOI 1: AASF. The Central Drainage 

Ditch (labeled AOI 2 in the PA) and IDANG AFFF Dump 1 (labeled AOI 3 in the PA) are being 

assessed by IDANG under a separate SI and are considered adjacent sources in this Report. The 

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

3.1 AOI 1 AASF

The Gowen Field AASF hangar, flight line, and apron are located in the southeast corner of the 

IDARNG Gowen Field AASF facility. The AASF consists of a main hangar (built between 2002 

and 2003), an enclosed wash rack (within a small hangar built between 2016 and 2017), an 

exterior wash rack area, flight line, small maintenance building, and an adjacent drainage field.

At the time of the PA, a 200-gallon Tri-MaxTM AFFF unit was stored inside the enclosed wash rack 

at the AASF and contains the only AFFF still on IDARNG property at Gowen Field AASF. The 

AFFF unit is a hose-operated system and is not connected to a suppression system in the 

building. There was no reported usage of this unit, and no evidence of spills or leaking in the 

vicinity (AECOM, 2019). Another 200 to 225-gallon Tri-MaxTM unit was stored outside of the main 

hangar, on the east end of the AASF. This unit is currently empty. Five empty extinguishers of 

various sizes (30-gallons or less) were also stored in this outdoor area. It is unclear what the 

contents of these extinguishers once were. Storm and floor drains on the flight line and inside the 

AASF hangars drain to the east and eventually discharge to the drain field adjacent to the AASF 

or to the sanitary sewer system (AECOM, 2019). Water entering the drain field flows through one 

of two grease/sand traps and is discharged to the subsurface via a ‘seepage trench’, which is a 

lined gravel pit. A valve system that can direct water off-site to the sanitary sewer system is also 

in place. 

Historically, Tri-MaxTM 30-gallon units that contained AFFF were discharged in the vicinity of the 

AASF from 2005 to 2015; there were about 12 to 15 30-gallon Tri-MaxTM units on the flight line 

during this time. It was reported that these units were fully expended before they were removed 

from the AASF, although the exact location of the foam discharge is unknown. Additionally, nozzle 

testing of the Tri-MaxTM units was conducted on the wash rack area and over the fence from the 

east compound into the adjacent grassy area about once every 3 years from 2005 to 2015. AFFF 

was also reportedly discharged on the flight line to clean up fuel spills on multiple occasions. The 

number of fuel spills and the quantity of AFFF used during these fuel spills are unknown (AECOM, 

2019). Information on AFFF storage and use at the AASF prior to the 1990s is unknown. 

3.2 Adjacent Sources

Nine off-facility potential sources were identified adjacent to Gowen Field AASF during the PA and 

are not associated with ARNG activities. The adjacent potential sources are shown on Figure 3-

1 and briefly described below for informational purposes only and were not investigated as part 

of this SI.

• IDANG Former FTA #1: An unlined training area at which AFFF was released directly 

to the ground surface. Located cross-gradient of AOI 1 but is located directly adjacent 

to the Central Drainage Ditch that eventually flows onto IDARNG property. 

• IDANG Former FTA #2: Area used for fire training activities with possible use of AFFF. 

Located upgradient of AOI 1. 
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Gowen Field AASF, Boise, Idaho

AECOM 3-2

• City Burn Pit: Off-facility burn pit where Gowen Field fire personnel conducted fire 

training activities using AFFF. Located 1.6 miles east of Gowen Field, cross-gradient 

of AOI 1. 

• IDANG Hangar 148: Hangar equipped with an AFFF fire suppression system which 

has historically been tested with foam occasionally vacuumed up and disposed of at 

the AFFF Dump 2. Located upgradient of AOI 1. 

• IDANG Hangars 1529 and 1530: The attached hangars share an AFFF fire 

suppression system which has historically been tested with foam occasionally 

vacuumed up and disposed of at the AFFF Dump 2. Located upgradient of AOI 1. 

• IDANG Hangar 155: The hangar’s fire suppression system was equipped with AFFF 

until 2005. No reported releases have escaped the confines of the hangar. Located 

upgradient of AOI 1. 

• Fire Station (Building 138): AFFF is carried on four engines in the station with an 

additional 880 gallons of AFFF stored in 55-gallon drums with secondary containment 

measures in place. Located upgradient of AOI 1.

• IDANG AFFF Dump 2: One of two locations where AFFF released at IDANG hangars 

was occasionally disposed. Located upgradient of AOI 1. 

• 2012 Plane Crash: Location where IDANG responded to a private plane crash on the 

south side of the main runway, about 0.4 miles from IDARNG property, during which 

an unknown quantity of AFFF was used to extinguish flames. Located cross-gradient 

of AOI 1. 

In 2018, the IDANG conducted an SI for perfluorinated compounds at Gowen Field (Leidos, 2019). 

The IDANG SI evaluated the presence or absence of PFOS, PFOA, PFBS, PFNA, PFHpA, and 

PFHxS at the following eight potential release areas which are located upgradient or cross 

gradient of AOI 1: 

• IDANG Former FTA #1, 

• IDANG Hangar 148, 

• IDANG Hangar 1529, 

• IDANG Hangar 1530, 

• IDANG Hangar 155, 

• Fire Station (Building 138), 

• IDANG AFFF Dump 1 (AOI 3), and

• IDANG AFFF Dump 2. 

Three other potential release areas (IDANG Former FTA#2, 2012 Plane Crash, and Building 1515 

[Hush House]) were not evaluated during the 2018 IDANG SI. At the time of the 2018 IDANG SI, 

the only exceedances observed were PFOA and PFOS in groundwater at the IDANG Former FTA

#1. However, all potential release areas were recommended for further investigation due to 

presence of the relevant compounds in soil, surface water, sediment, and/or groundwater. 

Comparing the 2018 IDANG SI results to the current OSD screening levels, the following 

exceedances were observed:

• Upgradient of AOI 1

• At the Fire Station (Building 138), PFOA and PFHxS were detected in 

groundwater at concentrations of 8.3 J ng/L and 210 ng/L, respectively.
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Gowen Field AASF, Boise, Idaho

AECOM 3-3

• At the IDANG AFFF Dump #2, PFOS was detected in groundwater with a 

concentration of 27 J ng/L.

• Cross-gradient of AOI 1

• At the IDANG Former FTA #1, PFOS was detected up to 390 J μg/kg in shallow 

subsurface soil. Additionally, PFOS and PFNA were detected in groundwater at 

concentrations of 290 ng/L and 18 ng/L, respectively.

• At the IDANG AFFF Dump #1, PFOS was detected in groundwater with a 

concentration of 4 J ng/L. 

This information is presented for informational purposes only as these potential release areas 

have the potential to migrate towards the IDARNG facility. 
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Gowen Field AASF, Boise, Idaho

AECOM 4-1

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, 2021a), 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 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 Gowen Field AASF (AECOM, 2019); 

• 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, 2021a); 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). Off-facility sampling 

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

stakeholders will be notified, and necessary rights of entry will be obtained by ARNG with property 

owner(s). To determine the presence/absence of PFAS, soil sampling was confined to the top 50 feet 

of the upper geologic formation and groundwater was sampled at the first encountered water table 

aquifer. Temporal boundaries were limited to the summer season, which was the earliest available 

time field resources were available to complete the study. 

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, 2021a). 

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 
Site Inspection Report

Gowen Field AASF, Boise, Idaho

AECOM 4-2

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, 2021a). 

 
Site Inspection Report

Gowen Field AASF, Boise, Idaho

AECOM 5-1

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, Gowen Field, Boise, Idaho dated December 2019

(AECOM, 2019);

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

Gowen Field, Boise, Idaho dated July 2021 (AECOM, 2021a); and

• Final Site Safety and Health Plan, Gowen Field, Boise, Idaho dated March 2021 (AECOM,

2021b).

The SI field activities were conducted from 8 to 15 November 2021 and consisted of utility clearance, 

sonic boring, soil sample collection, permanent monitoring well installation, groundwater sample 

collection, water level gauging that included nearby off-facility monitoring wells, and land surveying. 

Field activities were conducted in accordance with the SI QAPP Addendum (AECOM, 2021a), 

except as noted in Section 5.10. 

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:

• Thirteen (13) soil samples from six boring locations;

• One (1) groundwater sample from one (1) new permanent monitoring well;

• Thirteen (13) quality assurance (QA)/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 Request Forms

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 

collection plan. The process encourages stakeholder involvement in the SI, beginning with 
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Gowen Field AASF, Boise, Idaho

AECOM 5-2

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 15 March 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, IDARNG, USACE, Idaho Department of Environmental 

Quality and ANG. 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, 2021a). 

A TPP Meeting 3 was held [date to be determined] after the Draft Final SI Report submittal to 

regulators and will discuss the results of the SI. Meeting minutes for TPP 3 are 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’s drilling subcontractor, Yellow Jacket Drilling Services placed a ticket with DIGLINE, Inc. 

Idaho utility clearance provider to notify them of intrusive work on 16 April 2021. However, 

because the AASF is a private facility, the participating DIGLINE, Inc. locators did not clear utilities 

at the entire facility. Therefore, AECOM contracted Ground Penetrating Radar Systems, LLC 

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

clearance of the proposed boring locations on 8 November 2021 with input from the AECOM field 

team and Gowen Field AASF 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

The potable water source used for decontamination of drilling equipment was confirmed to be 

acceptable for use in a PFAS investigation prior to the start of field activities. A sample from a 

potable water source at Gowen Field AASF was collected on 24 September 2021, prior to 

mobilization, and analyzed for PFAS by LC/MS/MS compliant with QSM 5.3 Table B-15. The 

results of the decontamination water sample 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, 2021a). 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

Soil samples were collected via sonic drilling methods in accordance with the SI QAPP Addendum 

(AECOM, 2021a). A 7-inch diameter core barrel with an 8-inch diameter override casing was used 

to collect continuous soil cores to the target depth at soil borings AOI01-01 and AOI01-02. At 

boring GOWEN-MW001, an 8-inch diameter core barrel with a 9-inch override casing was used 

to collect continuous soil cores to 97 feet bgs and then telescoped down to a 7-inch diameter core 

barrel with an 8-inch diameter override casing 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 
Site Inspection Report

Gowen Field AASF, Boise, Idaho

AECOM 5-3

procedures. The soil boring locations are shown on Figure 5-1, and depths are provided Table 

5-2.

Three discrete soil samples were collected for chemical analysis from borings AOI01-01 and 

AOI01-02: one surface soil sample (0 to 2 feet bgs), one subsurface soil sample(13 to 15 feet 

bgs), and one from the bottom of the boring (49 to 50 feet bgs). At boring GOWEN-MW001, 

discrete soil samples were collected from surface soil (0 to 2 feet bgs), subsurface soil (13 to 15 

feet bgs), and one (1) foot above the water table (202 to 203 feet bgs). Due to moisture found at 

145 to 146 feet bgs at boring GOWEN-MW001, a fourth soil sample was collected at 145 to 146 

feet bgs.

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 boring logs (Appendix E) 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. 

Soil borings were completed at depths of 50 feet bgs (AOI1-1, AOI1-2) and 220 feet bgs (GOWENMW001) during the SI at Gowen Field AASF. Borings encountered well-graded gravel with sand 

as the dominant lithology of the unconsolidated sediments between 0 and 50 feet bgs. Wellgraded sand with silt was found as the dominant lithology between 50 and 220 feet bgs. 

Intermittent isolated layers of silt, gravel, and poorly graded silty sand were also observed in the 

deeper boring. These observations are consistent with the understood land fill material and fluvial 

depositional environment.

Each soil sample was collected into laboratory-supplied PFAS-free high-density polyethylene 

(HDPE) bottles 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 for PFAS (LC/MS/MS compliant with QSM 5.3 Table B-15), TOC 

(USEPA Method 9060A) and pH (USEPA Method 9045D) and grain size (ASTM Method D-422) 

in accordance with the SI QAPP Addendum (AECOM, 2021a). 

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

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

same parameters as the accompanying samples. 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.

Sonic drilling technology borings were abandoned in accordance with the SI QAPP Addendum 

(AECOM, 2021a) using bentonite chips at completion of sampling activities. Borings were 

installed in grass areas to avoid disturbing concrete or asphalt surfaces. 

5.3 Permanent Well Installation and Groundwater Grab Sampling

During the SI, one permanent monitoring well was installed within or downgradient of potential 

source areas. The location of the well is shown on Figure 5-1. 

A TSI 150T sonic drill rig was used to install one 4-inch-diameter monitoring well (GOWENMW001). The monitoring well was constructed with Schedule 80 poly-vinyl chloride, flushthreaded 10-foot sections of riser, 0.010-inch slotted well screen, and a threaded bottom cap. The 

location and depth of the permanent well was determined based on the depth to groundwater. A 
Site Inspection Report

Gowen Field AASF, Boise, Idaho

AECOM 5-4

filter pack of 12/20 silica sand was installed in the annulus around the well screen to a minimum 

of 2 feet above the well screen. Bentonite (3/8 inches) was placed above the filter sand to 4 feet 

bgs and hydrated with water. The bentonite was allowed to set for 24 hours prior to well 

development in accordance with the SI QAPP Addendum (AECOM, 2021a). GOWEN-MW001 

was completed with a flush mount well vault. The screen interval of the groundwater monitoring 

well is provided in Table 5-3, and a Well Diagram is provided in Appendix E. 

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

(AECOM, 2021a). The newly installed monitoring well was developed more than 24 hours 

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

development, a HDPE bailer was lost in the well during sand/sediment removal. Efforts were 

made over several days to recover the bailer, but were unsuccessful due to sand lock. Additionally, 

a pipe recovery tool made of stainless steel was lost during the attempted bailer recovery. 

Therefore, the upper seven feet of the well screen was developed. Samples were collected no 

sooner than 24 hours following development via low-flow sampling methods using a Geotech® 

1.66- by 18-inch bladder pump with new, disposable PFAS-free, HDPE tubing. The well was

purged at a rate determined in the field to reduce draw down prior to sampling. Water quality 

parameters (e.g., temperature, specific conductance, pH, dissolved oxygen, and oxidationreduction potential) were measured using a water quality meter and recorded on the field 

sampling form (Appendix B2). 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 identify if there were any foaming. No foaming was 

noted in the groundwater sample.

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, 2021a).

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

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

same parameters as the accompanying samples. 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.

5.4 Synoptic Water Level Measurements

A synoptic groundwater gauging event was performed on 12 November 2021. Groundwater 

elevation measurements were collected from the new permanent monitoring well, as well as from 

seven existing off-facility monitoring wells located on IDANG property, adjacent to Gowen Field

AASF. 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 the well casing was surveyed by Idaho-licensed land surveyors following 

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

data from the newly installed well on the facility was collected on 12 November 2021 in the 

applicable Universal Transverse Mercator zone projection with North American Datum 1983 

(horizontal) and North American Vertical Datum 1988 (vertical). The surveyed well data are 

provided in Appendix B4. The off-facility IDANG well survey data was provided by IDANG via 

email.
Site Inspection Report

Gowen Field AASF, Boise, Idaho

AECOM 5-5

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, 2021a) and with the DA Guidance for 

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

Soil IDW (i.e., soil cuttings) and liquid IDW (i.e., purged groundwater and decontamination fluids) 

generated during SI activities were containerized in properly labeled 55-gallon drums (see SOP 

3-05). This IDW was not sampled for PFAS and will assume the PFAS characteristics of the

associated soil and groundwater samples collected from their source location.

Liquid IDW generated during SI activities (i.e., purge water, development water, and 

decontamination fluids) were contained in labeled, 55-gallon DOT-approved steel drums, and left 

onsite in a designated waste storage area. During the TPP 1&2 meeting, IDEQ requested that 

IDW generated within or adjacent to a former wood preserving operation Installation Restoration 

Program site also be sampled for additional analytes associated with those operations. The 

former wood preserving operation site is located partially within the footprint of the AASF’s 

southwestern boundary (Figure 5-1) and was addressed and managed by the IDANG. Based on 

the results of two (1987 and 1990) SIs conducted at the site, semi-volatile organic compounds 

(SVOCs), in the form of 2-methylnaphthalene, pentachlorophenol, and phenanthrene, have 

impacted site soil and primarily reside in the shallow surface layer (above 5 feet bgs), extending 

no deeper than 50 feet bgs. Although SVOC contamination was not anticipated during this current 

SI, liquid and soil IDW collected during the SI sampled for the SVOCs list of 2-methylnaphthalene, 

pentachlorophenol, and phenanthrene. SVOCs were not detected in either IDW sample, AOI1-1-

IDW and AOI1-2-IDW. Results of this analysis are presented in Appendix G. 

ARNG will coordinate waste profiling, transportation, and disposal of the solid IDW. ARNG will 

manage and dispose of the 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 Engineering, Science, and Technology, Inc., 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 at 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.

Liquid and soil IDW collected during the SI were analyzed for the SVOCs list of 2-

methylnaphthalene, pentachlorophenol, and phenanthrene by USEPA Method 8270D (SW-846).

5.8 Deviations from SI QAPP Addendum

Three deviations from the SI QAPP Addendum occurred during the SI fieldwork. The deviations 

are noted below and are documented in Field Change Request Forms (Appendix B3). 

• During the installation of the permanent monitoring well, the drilling team recommended the

use of an 8-inch core barrel and 9-inch override casing in place of a 6-inch barrel and 8-inch

casing to 97 feet, and subsequently a 7-inch core barrel and 8-inch override casing to 217

feet. This larger casing was used to create a larger well annulus to accommodate and
Site Inspection Report

Gowen Field AASF, Boise, Idaho

AECOM 5-6

construct the 4-inch diameter permanent monitoring well. This action was documented in a 

field change request form provided in Appendix B3. 

• On 12 November 2021, the catch basin that was selected as sediment sample location

AOI1-03 was observed by the field team to be free of sediment; thus, a sediment sample

could not be collected. Additional catch basins were evaluated as potential replacement

sample locations; however, they were also found to be free of sediment. Subsequently, to

maintain contiguous sample numbering in AOI 1, sample ID AOI1-03 was repurposed as a

supplemental surface soil sample in the vicinity of monitoring well GOWEN-MW001. This

action was documented in a field change request form provided in Appendix B3.

• On 10 November 2021, the field team observed an IDANG firetruck conducting nozzle

testing within AOI 1 and adjacent to AOI 1 in the grassy areas along the southeast and

southwest edges of the flight line. Although testing was suspected to be conducted with

water only (no foam observed), a third surface soil sample (0 to 2 feet bgs) (AOI01-03) was

collected within the drainage ditch southeast of AOI01-01. Two additional surface soil

samples, AOI01-04 and AOI01-05, were also collected southwest of AOI01-01. This action

was documented in a field change request form provided in Appendix B3.
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, Gowen Field, Boise, Idaho

Sample Identification

Sample

Collection 

Date/Time

Sample Depth 

(feet bgs) LC/MS/MS compliant with QSM 5.3 Table B-15 TOC (USEPA Method 9060A) pH (USEPA Method 9045D) Grain Size (ASTM D-422) SVOCs (USEPA Method 8270)* Comments

AOI1-01-SB-0-2 11/8/2021 11:15 0 - 2 x

AOI1-1-SB-13-15 11/12/2021 10:40 13 - 15 x x x x

AOI1-1-SB-13-15-D 11/12/2021 10:40 13 - 15 x x x FD

AOI1-1-SB-13-15-MS 11/12/2021 10:40 13 - 15 x x x MS

AOI1-1-SB-13-15-MSD 11/12/2021 10:40 13 - 15 x x x MSD

AOI1-1-SB-49-50 11/12/2021 11:20 49 - 50 x

AOI1-02-SB-0-2 11/8/2021 11:30 0 - 2 x

AOI1-2-SB-13-15 11/12/2021 8:35 13 - 15 x

AOI1-2-SB-49-50 11/12/2021 9:00 49 - 50 x

AOI1-3-SB-0-2 11/15/2021 10:25 0 - 2 x

AOI1-4-SB-0-2 11/15/2021 10:40 0 - 2 x

AOI1-4-SB-0-2-D 11/15/2021 10:40 0 - 2 x FD

AOI1-5-SB-0-2 11/15/2021 10:55 0 - 2 x

GOWEN-MW001-SB-0-2 11/8/2021 10:45 0 - 2 x

GOWEN-MW001-SB-13-15 11/8/2021 15:15 13 - 15 x

GOWEN-MW001-SB-145-146 11/8/2021 13:15 145 - 146 x

GOWEN-MW001-SB-202-203 11/8/2021 16:50 202 - 203 x

AOI1-1-IDW 11/12/2021 11:50 NA x Composite

AOI1-2-IDW 11/12/2021 11:55 NA x Composite

GOWEN-MW001-GW 11/15/2021 10:05 NA x

GOWEN-MW001-GW-D 11/15/2021 10:05 NA x FD

GOWEN-MW001-GW-MS 11/15/2021 10:05 NA x MS

GOWEN-MW001-GW-MSD 11/15/2021 10:05 NA x MSD

GOWEN-FRB-01 11/15/2021 14:00 NA x

GOWEN-ERB-01 11/8/2021 13:00 NA x from drill rig hose

GOWEN-ERB-02 11/8/2021 14:45 NA x from hand auger

GOWEN-ERB-03 11/13/2021 14:00 NA x from drill bit

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

SVOCs = semi-volatile organic compounds

TOC = total organic carbon

USEPA = United States Environmental Protection Agency

*SVOC analysis conducted for investigation-derived waste characterization per Idaho Department of Environmental Quality.

Soil Samples

Quality Control Samples

Groundwater Samples

AECOM 5-7
Table 5-2

Soil Boring Depths

Site Inspection Report, Gowen Filed, Boise, Idaho

Area of 

Interest

Boring 

Location

Soil Boring 

Depth 

(feet bgs) Start Date End Date

AOI1-1 50 11/12/21 10:30 AM 11/12/21 11:30 AM

AOI1-2 50 11/12/21 7:55 AM 11/12/21 9:30 AM

GOWEN-MW001 220 11/8/21 2:50 PM 11/11/21 3:15 PM

Notes:

bgs = below ground surface

1

AECOM 
Table 5-3

Permanent Monitoring Well Screen Intervals and Groundwater Elevations

Site Inspection Report, Gowen Filed, Boise, Idaho

Area of 

Interest

Boring 

Location

Soil 

Boring 

Depth 

(feet bgs)

Monitoring 

Well Screen 

Interval 

(feet bgs)

Top of 

Casing 

Elevation 

(feet 

NAVD88)

Ground 

Surface 

Elevation 

(feet 

NAVD88)

Depth to 

Water

(feet 

btoc)

Depth to 

Water

(feet bgs)

Groundwater 

Elevation

(feet NAVD88)

1

GOWENMW001 220 207-217 2,852.43 2852.77 204.21 204.55 2,648.22

MW-1-

PRL01 unknown 204.65-214.65 2,847.66 unknown 198.24 unknown 2,649.42

RIMW-2 unknown 205-215 2,850.98 unknown 201.18 unknown 2,649.80

MW-3-

PRL01 unknown 205-215 2,849.40 unknown 200.67 unknown 2,649.32

RIMW-4 unknown 203-213 2,852.26 unknown 202.52 unknown 2,649.74

MW-5-

PRL01 unknown 210.62-220.62 2,856.30 unknown 206.77 unknown 2,649.53

MW-BOI10 unknown 200-220 2,853.94 unknown 206.15 unknown 2,647.79

MW-BOI11 unknown 190-210 2,830.30 unknown 163.71 unknown 2,666.59

ANG 

Wells

AECOM 5-9
Site Inspection Report

Gowen Field AASF, Boise, Idaho

AECOM 5-10

THIS PAGE INTENTIONALLY BLANK
"?!S "S

!?

A!

A!

A!

A!

A!

A!

A!

"S

?!

Former 

Wood Preserving Operation

ID ANG AFFF Dump 1

AASF

Central Drainage Ditch

AOI 1 AOI01-01

AOI01-04

AOI01-03

GOWEN-MW001

MW-1-PRL01

RIMW-2

MW-3-PRL01

RIMW-4

MW-5-PRL01

MW-BOI10-01

MW-BOI11-01

AOI01-05

AOI01-02

Legend

!? Soil Boring/Permanent Monitoring Well

?! Soil Boring

A! Existing Monitoring Well

"S Surface Soil Sample

Area of Interest

Potential Release Area

Facility Boundary

Underground Culvert

Canal/Ditch

Surface Water Flow Direction

Groundwater Flow Direction

0 250 500 1,000

Feet

Site Inspection Sample Locations

Figure 5-1

CLIENT

REVISED

SCALE

10/28/2022 MS

CH

10/28/2022

10/28/2022

ARNG

GIS BY

CHK BY

PROJECT Site Inspection at Gowen Field AASF, ID

PM CM 10/28/2022

1:6,000 ­ 12420 Milestone Center Drive

Germantown, MD 20876

Base Map: Sources: Esri, HERE, Garmin, USGS, Intermap, INCREMENT P, NRCan, Esri

Japan, METI, Esri China (Hong Kong), Esri Korea, Esri (Thailand), NGCC, (c)

AECOM 5-11
AECOM 5-12

THIS PAGE INTENTIONALLY BLANK

Site Inspection Report

Gowen Field AASF, Boise, Idaho
Site Inspection Report

Gowen Field AASF, Boise, Idaho

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

through Section 6.5. 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 against the SLs presented in Table 6-1. The

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

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

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

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

Gowen Field AASF, Boise, Idaho

AECOM 6-2

6.2 Soil Physicochemical Analyses

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

size, which are important for evaluating transport through the soil medium. Appendix F contains

the results of the TOC, pH, and grain size analyses.

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: AASF . 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. As noted in

Section 5.8, AOI01-03 was repurposed as a supplemental surface soil sample in the vicinity of

monitoring well GOWEN-MW001.

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.

Soil was sampled at three soil boring locations and three surface soil locations surrounding the

AOI. At each of the three soil boring locations, AOI01-01, AOI01-02, and GOWEN-MW001, three

soils samples were collected: the shallow surface interval (0 to 2 feet bgs), the deep interval

(bottom of boring at AOI01-01 and AOI01-02, and two feet above groundwater at GOWENMW001), and the intermediate interval (13 to 15 feet bgs). Due to moisture found at 145 to 146

feet bgs at boring GOWEN-MW001, a fourth soil sample was collected at 145 to 146 feet bgs. At

the three remaining locations located within the eastern portion of the potential release area,

AOI01-03, AOI01-04, and AOI01-05, a sample was collected from only the surface soil interval (0

to 2 feet bgs).

PFOA, PFOS and PFHxS exceeded their respective SLs in surface soil at AOI 1, both within and

downgradient of the potential release area and the location of the IDARNG fire tuck nozzle check

observed during the SI fieldwork. Surface soil detections included the following

 PFOS exceeded the OSD SL of 13 micrograms per kilogram (μg/kg) at every location

with concentrations ranging between 35.0 μg/kg to 359 μg/kg.

 At location GOWEN-MW001, PFOA exceeded the OSD SL of 19 μg/kg at a

concentration of 19.5 μg/kg and PFHxS exceeded the OSD SL of 130 μg/kg at a

concentration of 236 μg/kg.

 PFBS was detected at every location at a maximum concentration of 2.46 μg/kg, three

orders of magnitude below the OSD SL of 1900 μg/kg.
Site Inspection Report

Gowen Field AASF, Boise, Idaho

AECOM 6-3

 PFNA was detected in surface soil at every location, except AOI01-02, at a maximum

concentration of 7.37 μg/kg.

PFOS was detected at AOI01-01 in both the shallow subsurface (13 to 15 feet bgs) and at the

deep interval (49 to 50 feet bgs), at concentrations of 0.662 J μg/kg and 1.50 μg/kg, respectively.

PFHxS was also detected at AOI01-01 in both the shallow subsurface (13 to 15 feet bgs) and at

the deep interval (49 to 50 feet bgs) at concentrations of 0.033 J μg/kg and 0.079 μg/kg,

respectively. PFNA was detected at the deep interval at AOI01-01 at a concentration of 0.042 J

μg/kg. These concentrations of PFOS, PFHxS, and PFNA are several orders of magnitude below

the SLs. PFOA and PFBS were not detected in any shallow subsurface or deep soil location.

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 one permanent monitoring well GOWEN-MW001. PFOS was

detected below the SL at a concentration of 1.87 ng/L. PFOA, PFHxS, PFNA, and PFBS were not

detected groundwater at AOI 1.

6.3.3 AOI 1 Conclusions

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

concentrations above their respective SLs. Exceedances in surface soil adjacent to and

downgradient of AOI 1 may be the result of ANG activities. PFOS was detected in groundwater at

a concentration below the SL. Based on the exceedances of the SLs in soil, further evaluation at

AOI 1 is warranted.
Site Inspection Report

Gowen Field AASF, Boise, Idaho

AECOM 6-4

THIS PAGE INTENTIONALLY BLANK
Table 6-2

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

Site Inspection Report, Gowen Field

Analyte OSD Screening 

Level a

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

PFBS 1900 0.089 J 0.046 J 0.825 J 0.025 J 0.035 J 0.115 J 2.46PFHxS 130 3.90 0.106 J 17.7 0.283 J 0.303 J 5.50 236PFNA 19 1.62 ND U 0.277 J 7.37 5.08 5.96 0.348 JPFOA 19 2.49 ND U 3.78 5.59 4.60 6.53 19.5PFOS 13 56.9 ND U 359 42.3 35.0 39.1 131

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acidPFOA perfluorooctanoic acidPFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AOI Area of InterestU = The analyte was not detected at a level greater than or equal to the adjusted DL D duplicate

DL detection limit

Notes ft feetND = Analyte not detected above the LOD. LOD values are presented in Appendix F. HQ hazard quotient

ID identificationLCMSMS liquid chromatography with tandeLOD limit of detectionND analyte not detected above the LOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierSB soil boringUSEPA United States Environmental Protμg/kg micrograms per kilogram

Area of Interest

Sample ID

Sample Date

Depth

AOI01-01-SB-0-2

11/08/2021

0-2 ft

11/08/2021

0-2 ft

AOI01-03-SB-0-2

11/15/2021

0-2 ft

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.

AOI01

AOI01-05-SB-0-2

11/15/2021

0-2 ft

GOWEN-MW001-SB-0-2

11/08/2021

0-2 ft

AOI01-04-SB-0-2

11/15/2021

0-2 ft

AOI01-04-SB-0-2-D

11/15/2021

0-2 ft

AOI01-02-SB-0-2

AECOM 
Table 6-3

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

Site Inspection Report, Gowen Field

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual

PFBS 25000 ND U ND U ND U ND UPFHxS 1600 0.033 J ND U ND U ND UPFNA 250 ND U ND U ND U ND UPFOA 250 ND U ND U ND U ND UPFOS 160 0.662 J 0.310 J ND U ND U

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acidPFOA perfluorooctanoic acidPFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AOI Area of InterestU = The analyte was not detected at a level greater than or equal to the adjusted DL D duplicate

DL detection limit

Notes ft feet

ND = Analyte not detected above the LOD. LOD values are presented in Appendix F. HQ hazard quotient

ID identificationLCMSMS liquid chromatography with tanLOD 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 Pμg/kg micrograms per kilogram

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.

AOI01

GOWEN-MW001-SB-13-15

11/08/2021

13-15 ft

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

AOI01-01-SB-13-15-D

11/12/2021

13-15 ft

AOI01-02-SB-13-15

11/12/2021

13-15 ft

Area of Interest

Sample ID

Sample Date

Depth

AOI01-01-SB-13-15

11/12/2021

13-15 ft

AECOM 
Table 6-4

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

Site Inspection Report, Gowen Field

Area of Interest

Sample ID

Sample Date

Depth

Analyte Result Qual Result Qual Result Qual Result Qual

PFBS ND U ND U ND U ND UPFHxS 0.079 J ND U ND U ND UPFNA 0.042 J ND U ND U ND UPFOA ND U ND U ND U ND U

PFOS 1.50 ND U ND U ND U

Interpreted Qualifiers Chemical AbbreviationsJ = Estimated concentration PFBS perfluorobutanesulfonU = The analyte was not detected at a level greater than or equal to the adjusted DL PFHxS perfluorohexanesulfon

PFNA perfluorononanoic acid

Notes PFOA perfluorooctanoic acid

ND = Analyte not detected above the LOD. LOD values are presented in Appendix F. PFOS perfluorooctanesulfon

Acronyms and Abbreviations

AOI Area of InterestD duplicateDL detection limitft feetID identificationLCMSMS liquid chromatography LOD limit of detectionND analyte not detected aQSM Quality Systems ManuQual interpreted qualifierSB soil boringμg/kg micrograms per kilogra

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

AOI01

GOWEN-MW001-SB-145-146

11/08/2021

145-146 ft

GOWEN-MW001-SB-202-203

11/08/2021

202-203 ft

AOI01-01-SB-49-50

11/12/2021

49-50 ft

AOI01-02-SB-49-50

11/12/2021

49-50 ft

AECOM 
Table 6-5

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

Site Inspection Report, Gowen Field

Analyte OSD Screening 

Level a

Result Qual Result Qual

PFBS 601 ND U ND UPFHxS 39 ND U ND UPFNA 6 ND U ND UPFOA 6 ND U ND UPFOS 4 1.87 J 1.85 J

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acidPFOA perfluorooctanoic acidPFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AOI Area of InterestU = The analyte was not detected at a level greater than or equal to the adjusted DL D duplicate

DL detection limit

Notes GW groundwater

ND = Analyte not detected above the LOD. LOD values are presented in Appendix F. HQ hazard quotient

ID identificationLCMSMS liquid chromatography with tandem LOD limit of detectionND analyte not detected above the LOOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierUSEPA United States Environmental Proteng/l nanogram per liter

GOWEN-MW001-GW-D

11/15/2021

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.

Area of Interest AOI01

Sample ID

Sample Date

GOWEN-MW001-GW

11/15/2021

AECOM 
Former 

Wood Preserving Operation

AOI01-01

AOI01-04

AOI01-03

GOWEN-MW001

AOI01-05

AOI01-02

Former 

Wood Preserving Operation AOI01-01

GOWEN-MW001

AOI01-02

Former 

Wood Preserving Operation

GOWEN-MW001

145 ft - 146 ft: ND 

202 ft - 203 ft: ND

AOI01-02

AOI01-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-1

PFOA Detections in Soil

8/17/2022

8/17/2022

MS 8/17/2022

EG

CM

GIS BY

CHK BY

PM

8/17/2022

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Gowen Field AASF, ID

Base Map: Sources: Esri, HERE, Garmin, USGS, Intermap,

INCREMENT P, NRCan, Esri Japan, METI, Esri China (Hong

1:2,400

Shallow

Intermediate

Deep

0 100 200 400

­

Feet

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

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

Facility Boundary PFOA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

AECOM 6-9
Former 

Wood Preserving Operation AOI01-01

AOI01-04 AOI01-03

GOWEN-MW001

AOI01-05

AOI01-02

Former 

Wood Preserving Operation AOI01-01

GOWEN-MW001

AOI01-02

Former 

Wood Preserving Operation

GOWEN-MW001

145 ft - 146 ft: ND

202 ft - 203 ft: ND

AOI01-02

AOI01-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-2

PFOS Detections in Soil

8/17/2022

8/17/2022

MS 8/17/2022

EG

CM

GIS BY

CHK BY

PM

8/17/2022

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Gowen Field AASF, ID

Base Map: Sources: Esri, HERE, Garmin, USGS, Intermap,

INCREMENT P, NRCan, Esri Japan, METI, Esri China (Hong

1:2,400

Shallow

Intermediate

Deep

0 100 200 400

­

Feet

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

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

Facility Boundary PFOS Results (μg/Kg)

ND

>ND - 13

>13 - 160

>160 - 1,600

>1,600

AECOM 6-10
Former 

Wood Preserving Operation

AOI01-01

AOI01-04

AOI01-03

GOWEN-MW001

AOI01-05

AOI01-02

Former 

Wood Preserving Operation AOI01-01

GOWEN-MW001

AOI01-02

Former 

Wood Preserving Operation

GOWEN-MW001

145 ft - 146 ft: ND

202 ft - 203 ft: ND

AOI01-02

AOI01-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-3

PFBS Detections in Soil

8/17/2022

8/17/2022

MS 8/17/2022

EG

CM

GIS BY

CHK BY

PM

8/17/2022

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Gowen Field AASF, ID

Base Map: Sources: Esri, HERE, Garmin, USGS, Intermap,

INCREMENT P, NRCan, Esri Japan, METI, Esri China (Hong

1:2,400

Shallow

Intermediate

Deep

0 100 200 400

­

Feet

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

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

Facility Boundary PFBS Results (μg/Kg)

ND

>ND - 10

>10 - 1,900

>1,900 - 25,000

>25,000

AECOM 6-11
Former 

Wood Preserving Operation

AOI01-01

AOI01-04

AOI01-03

GOWEN-MW001

AOI01-05

AOI01-02

Former 

Wood Preserving Operation

AOI01-01

GOWEN-MW001

AOI01-02

Former 

Wood Preserving Operation

GOWEN-MW001

145 ft - 146 ft: ND

202 ft - 203 ft: ND

AOI01-02

AOI01-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-4

PFHxS Detections in Soil

8/17/2022

8/17/2022

MS 8/17/2022

EG

CM

GIS BY

CHK BY

PM

8/17/2022

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Gowen Field AASF, ID

Base Map: Sources: Esri, HERE, Garmin, USGS, Intermap,

INCREMENT P, NRCan, Esri Japan, METI, Esri China (Hong

1:2,400

Shallow

Intermediate

Deep

0 100 200 400

­

Feet

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

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

Facility Boundary PFHxS Results (μg/Kg)

ND

>ND - 10

>10 - 130

>130 - 1,600

>1,600

AECOM 6-12
Former 

Wood Preserving Operation

AOI01-01

AOI01-04

AOI01-03

GOWEN-MW001

AOI01-05

AOI01-02

Former 

Wood Preserving Operation

AOI01-01

GOWEN-MW001

AOI01-02

Former 

Wood Preserving Operation

GOWEN-MW001

145 ft - 146 ft: ND

202 ft - 203 ft: ND

AOI01-02

AOI01-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-5

PFNA Detections in Soil

8/17/2022

8/17/2022

MS 8/17/2022

EG

CM

GIS BY

CHK BY

PM

8/17/2022

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Gowen Field AASF, ID

Base Map: Sources: Esri, HERE, Garmin, USGS, Intermap,

INCREMENT P, NRCan, Esri Japan, METI, Esri China (Hong

1:2,400

Shallow

Intermediate

Deep

0 100 200 400

­

Feet

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

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

Facility Boundary PFNA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

AECOM 6-13
GOWEN-MW001

AOI 1

GOWEN-MW001

GOWEN-MW001

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-6

PFOA, PFOS, and PFBS Detections 

in Groundwater

10/5/2022

10/5/2022

MS 10/5/2022

EG

CM

GIS BY

CHK BY

PM

10/5/2022

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Gowen Field AASF, ID

Base Map: Sources: Esri, HERE, Garmin, USGS, Intermap,

INCREMENT P, NRCan, Esri Japan, METI, Esri China (Hong

1:2,400

Facility Boundary

Groundwater Flow Direction

PFOA

PFOS

PFBS

0 100 200 400

­

Feet

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

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 6-14
GOWEN-MW001

AOI 1

GOWEN-MW001

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-7

PFHxS and PFNA Detections

in Groundwater

8/17/2022

8/17/2022

MS 8/17/2022

EG

CM

GIS BY

CHK BY

PM

8/17/2022

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Gowen Field AASF, ID

Base Map: Sources: Esri, HERE, Garmin, USGS, Intermap,

INCREMENT P, NRCan, Esri Japan, METI, Esri China (Hong

1:2,400

Facility Boundary

Groundwater Flow Direction

PFHxS

PFNA

0 100 200 400

­

Feet

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

PFHxS Results (ng/L)

ND

>ND - 39

>39 - 100

>100 - 1,000

>1,000

PFNA Results (ng/L)

ND

>ND - 6

>6 - 100

>100 - 1,000

>1,000

AECOM 6-15
THIS PAGE INTENTIONALLY BLANK

AECOM 6-16

Site Inspection Report

Gowen Field AASF, Boise, Idaho
Site Inspection Report

Gowen Field AASF, Boise, Idaho

AECOM 7-1

7. Exposure Pathways

The CSM for AOI 1, 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 figure uses 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 above the SLs. Areas with an identified potentially complete pathway that have 

detections of the relevant compounds above the SLs may warrant further investigation. Although 

the CSM indicates whether potentially complete exposure pathways may exist, the 

recommendation for future study in a 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), and residents outside 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 based on the aforementioned criteria. 

7.1.1 AOI 1

Between 2005 and 2015, AFFF may have been released at AOI 1 during Tri-Max use, AFFF 

storage by IDARNG adjacent to the small maintenance building and drainage field, and nozzle 

checks by IDANG's fire truck observed during the SI fieldwork. 

PFOA, PFOS, PFHxS, PFNA, and PFBS were detected in surface soil at AOI 1, with PFOA, PFOS 

and PFHxS exceeding their respective SLs. Site workers and construction workers could contact 
Site Inspection Report

Gowen Field AASF, Boise, Idaho

AECOM 7-2

constituents in surface soil via incidental ingestion and inhalation of dust. Additionally, off-facility 

trespassers may potentially be exposed to PFOA, PFOS, and PFBS via inhalation of dust caused 

by on-facility ground disturbing activities. Therefore, the surface soil exposure pathway for site 

workers, construction workers, and trespassers are potentially complete. PFOS, PFHxS, and 

PFNA were detected in subsurface soil at AOI 1. No active construction was observed during SI 

field activities; however, future construction workers could contact constituents in subsurface soil 

via incidental ingestion, and therefore, the subsurface soil exposure pathway for construction 

workers is potentially complete. Residential structures are not present at AOI 1, therefore the 

resident soil exposure pathway is incomplete. The CSM for AOI 1 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

PFOS was detected at a concentration below the SL in groundwater at permanent monitoring well 

GOWEN-MW001, which is inferred to be cross or downgradient of the potential PFAS release 

area. Drinking water for Gowen Field AASF is supplied by a local supplier, Suez, which uses three 

public supply wells that are located within 2 miles of the facility boundary. However, recharge for 

the deep aquifer does not occur in the Gowen Field AASF footprint, and it is unlikely that these 

wells will be impacted; therefore, the deep groundwater pathway to all receptors is incomplete

(Leidos, 2019). Additionally, groundwater was observed at a depth of 204.21 feet bgs; therefore, 

the exposure pathway for future construction workers is incomplete. Several private water or 

irrigation wells are located downgradient of AOI 1 that may be screened in the shallow aquifer 

and could potentially be impacted by the PFAS release at AOI 1. Therefore, the exposure pathway 

for groundwater to off-facility residents is potentially complete. The CSM 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 sediment and surface water via 

leaching and run-off. Surface drainage at Gowen Field AASF is controlled both by the local surface 

topography, piped stormwater catch basins and a system of drainage ditches. The nearest 

drainage ditch generally traverses the facility, with flow from east to west. This drainage ditch, the 

Central Drainage Ditch, originates as the remnant of an intermittent stream on the adjacent 

IDANG property before traversing the IDARNG property and discharging to an off-facility retention 

pond. Additionally, IDANG Former FTA #1, adjoining the Central Drainage Ditch, exhibited PFOS 

in the soil (390 μg/kg, sample interval 13 to 15 feet bgs) and groundwater (290 ng/L) (Leidos, 

2019). PFOA, PFOS, PFHxS, PFNA, and PFBS were detected in soil and groundwater at AOI 1, 

therefore, the surface water and sediment ingestion exposure pathway for site workers, future 

construction workers, and trespassers is considered potentially complete. The PA did not identify 

any IDARNG potential release areas along the Central Drainage Ditch. The FTA #1 and Central 

Drainage Ditch are being assessed by IDANG under the ANG PFAS program. Because the off-
Site Inspection Report

Gowen Field AASF, Boise, Idaho

AECOM 7-3

facility retention pond has no known recreational uses, the surface water and sediment ingestion 

exposure pathway for off-facility residents and recreational users is considered incomplete.
Site Inspection Report

Gowen Field AASF, Boise, Idaho

AECOM 7-4

THIS PAGE INTENTIONALLY BLANK
Media

SOURCE PATHWAY RECEPTOR

AOI 1

Nozzle testing

and fuel spill

response

Surface soil

Human

activities

Precipitation/

run-off

Leaching/

infiltration

Airborne soil

particulate

Surface soil at

AOI

Surface water/

sediment

Subsurface

soil

Shallow

groundwater2

Source Release

Mechanism Media Transportand Migration Media ExposureRoutes

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

Potentially Complete Pathway

with Exceedance of SL

/ / / /

Site

Worker

Construction 

Worker3 Resident1

Trespasser

Site

Worker

Construction 

Worker3 Resident1

/ / / /

/ / / /

/ / / /

/ / / /

LEGEND

Figure 7-1

Conceptual Site Model, AOI 1

Gowen Field AASF

Potential

Off-Facility

Source Not

under

Control of

ARNG

Trespasser

1. The resident refers to off-site receptors.

2. Exposure pathways for groundwater in the

deep aquifer is incomplete for all receptors.

3. No current active construction at the facility.

Notes:

7-5
THIS PAGE INTENTIONALLY BLANK

AECOM 

Site Inspection ReportGowen Field AASF, Boise, Idaho
Site Inspection Report

Gowen Field AASF, Boise, Idaho

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 8 to 15 November 2021 and consisted of utility clearance, 

sonic soil boring installation, soil sample collection, permanent monitoring well installation, 

groundwater sample collection, and land surveying. Field activities were conducted in accordance 

with the SI QAPP Addendum (AECOM, 2021a), except as previously noted in Section 5.10. 

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

• Thirteen (13) soil samples from six boring locations; 

• One groundwater sample from one permanent monitoring well; 

• Thirteen (13) 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 the AOI 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 AOI, 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 (see Table 8.1). 

Based on the CSMs developed and revised in light of the SI findings, there is not a complete 

pathway between source and on-facility drinking water receptors at this time. However, due to the 

limited groundwater data collected during the SI, further evaluation of the groundwater pathway

is necessary during the RI. Sample analytical concentrations collected during the SI were 

compared to the risk-based 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: 

• PFOA, PFOS and PFHxS exceeded their respective SLs in surface soil. PFOA 

exceeded the SL of 19 μg/kg with a concentration of 19.5 μg/kg at GOWEN-MW001. 

PFOS exceeded the SL of 13 μg/kg with a maximum concentration of 359 μg/kg at 

AOI01-03. PFHxS exceeded the SL of 130 μg/kg with a concentration of 236 μg/kg 

at GOWEN-MW001. AOI01-03 is located within AOI 1, and GOWEN-MW001 is 

located adjacent to and downgradient of AOI 1. Exceedances in surface soil adjacent 

to and downgradient of AOI 1 may be the result of ANG activities. Based on the 

results of the SI, further evaluation of AOI 1 is warranted in the RI.

• The detected concentrations of PFOS in groundwater at AOI 1 was below the SL.

The sampled well is near the facility property boundary.
Site Inspection Report

Gowen Field AASF, Boise, Idaho

AECOM 8-2

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

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

the CSM developed during the PA and revised based on SI findings, the presence of HFPO-DA 

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

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

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

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

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

Groundwater –

Facility 

Boundary

Future Action

1 AASF Proceed to RI 

Legend:

N/A = not applicable 

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected
Site Inspection Report

Gowen Field AASF, Boise, Idaho

AECOM 9-1

9. References

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W912DR17F0192. 9 March.

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Contract No. W912DR-12-D-0014/W912DR17F0192. July. 

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AECOM 9-2

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