FINAL

Site Inspection Report 

Camp Guernsey

Guernsey, Wyoming

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

August 2023

Prepared for:

Army National Guard Bureau

111 S. George Mason Drive

Arlington, VA 22204

UNCLASSIFIED
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Camp Guernsey, Wyoming

AECOM i

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 ......................................................................................................2-2

2.2.2 Hydrogeology..............................................................................................2-3

2.2.3 Hydrology....................................................................................................2-4

2.2.4 Climate........................................................................................................2-5

2.2.5 Current and Future Land Use......................................................................2-5

2.2.6 Sensitive Habitat and Threatened/ Endangered Species.............................2-5

2.3 History of PFAS Use..............................................................................................2-6

3. Summary of Areas of Interest .......................................................................................3-1

3.1 AOI 1 Camp Guernsey Airfield ..............................................................................3-1

3.2 AOI 2 Current Firetruck Maintenance Areas ..........................................................3-2

3.3 AOI 3 Historic Maintenance and Storage Areas.....................................................3-2

3.4 AOI 4 Outdoor Wash Rack ....................................................................................3-3

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 Groundwater Sampling Point Installation and Groundwater 

Sampling...........................................................................................................5-4

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

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

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

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

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

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

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

6.2 Soil Physicochemical Analyses .............................................................................6-2

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

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

6.3.2 AOI 1 Groundwater Analytical Results.........................................................6-2
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6.3.3 AOI 1 Conclusions ......................................................................................6-3

6.4 AOI 2.....................................................................................................................6-3

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

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

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

6.5 AOI 3.....................................................................................................................6-4

6.5.1 AOI 3 Soil Analytical Results .......................................................................6-4

6.5.2 AOI 3 Groundwater Analytical Results.........................................................6-4

6.5.3 AOI 3 Conclusions ......................................................................................6-4

6.6 AOI 4.....................................................................................................................6-5

6.6.1 AOI 4 Soil Analytical Results .......................................................................6-5

6.6.2 AOI 4 Groundwater Analytical Results.........................................................6-5

6.6.3 AOI 4 Conclusions ......................................................................................6-5

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

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

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

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

7.1.3 AOI 3...........................................................................................................7-2

7.1.4 AOI 4...........................................................................................................7-3

7.2 Groundwater Exposure Pathway...........................................................................7-3

7.2.1 AOI 1...........................................................................................................7-3

7.2.2 AOI 2...........................................................................................................7-4

7.2.3 AOI 3...........................................................................................................7-4

7.2.4 AOI 4...........................................................................................................7-4

7.3 Surface Water and Sediment Exposure Pathway ..................................................7-4

7.3.1 AOI 1...........................................................................................................7-4

7.3.2 AOI 2...........................................................................................................7-5

7.3.3 AOI 3 and 4.................................................................................................7-5

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. Nonconformance and Corrective Action Reports

B5. Survey Data

B6. Investigation-Derived Waste Polygons

Appendix C Photographic Log

Appendix D TPP Meeting Minutes

Appendix E Boring Logs and Groundwater Sample 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, May 2022

Figure 2-5 Surface Water Features

Figure 3-1 Areas of Interest

Figure 5-1 Site Inspection Sample Locations

Figure 6-1 PFOA Detections in Soil

Figure 6-2 PFOS Detections in Soil

Figure 6-3 PFBS Detections in Soil

Figure 6-4 PFHxS Detections in Soil

Figure 6-5 PFNA Detections in Soil

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

Figure 6-7 PFHxS and PFNA Detections in Groundwater

Figure 7-1 Conceptual Site Model, AOI 1

Figure 7-2 Conceptual Site Model, AOI 2

Figure 7-3 Conceptual Site Model, AOI 3

Figure 7-4 Conceptual Site Model, AOI 4

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 and Permanent Groundwater Sampling Point Screen 

Intervals

Table 5-3 Permanent Groundwater Sampling Point Screen Intervals and Groundwater 

Elevations

Table 6-1 Screening Levels (Soil and Groundwater)

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

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

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

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

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

% percent

°C degrees Celsius

°F degrees Fahrenheit

μg/kg micrograms per kilogram

AECOM AECOM Technical Services, Inc.

AFFF aqueous film-forming foam

AOI Area of Interest

ARNG Army National Guard

bgs below ground surface 

BLM Bureau of Land Management

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act 

cfs cubic feet per second

CoC chain of custody

CSM conceptual site model

CSMS Combined Support Maintenance Shop

DA Department of the Army

DoD Department of Defense

DQO data quality objective

DUA data usability assessment

ELAP Environmental Laboratory Accreditation Program

EM Engineer Manual

FedEx Federal Express

FMS Field Maintenance Shop

GPS global positioning system

GPRS Ground Penetrating Radar Systems

HDPE high-density polyethylene 

HFPO-DA hexafluoropropylene oxide dimer acid

HSA hollow stem auger

IDW investigation-derived waste

ITRC Interstate Technology Regulatory Council

LC/MS/MS liquid chromatography with tandem mass spectrometry

MIL-SPEC military specification

NELAP National Environmental Laboratory Accreditation Program

ng/L nanograms per liter

NTA North Training Area

OSD Office of the Secretary of Defense

PA Preliminary Assessment

PFAS per- and polyfluoroalkyl substances

PFBS perfluorobutanesulfonic acid

PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid
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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

STA South Training Area

TOC total organic carbon

TPP Technical Project Planning

UFP Uniform Federal Policy

US United States

USACE United States Army Corps of Engineers

USACHPPM United States Army Center for Health Promotion and Preventative Medicine

USCS Unified Soil Classification System

USEPA United States Environmental Protection Agency

USFWS United States Fish and Wildlife Service

USGS United States Geological Survey

UTES Unit Training Equipment Site

WSGS Wyoming State Geological Survey

WYARNG Wyoming Army National Guard

WYDEQ Wyoming Department of Environmental Quality
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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. 

Four Areas of Interest (AOIs) were identified in the PA and during SI Quality Assurance Project 

Plan (QAPP) Addendum (AECOM, 2021) development where PFAS-containing materials may 

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

The objective of the SI is to identify whether there has been a release to the environment from 

the AOIs identified in the PA and SI QAPP Addendum 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 Camp Guernsey in 

Guernsey, Wyoming and determined further evaluation under the Comprehensive Environmental 

Response, Compensation, and Liability Act (CERCLA) is warranted for AOI 1 and AOI 4; no further 

evaluation is warranted for AOI 2 and AOI 3 at this time. Camp Guernsey will also be referred to 

as the “facility” throughout this document.

Camp Guernsey partially surrounds the towns of Guernsey and Hartville, in Platte County, 

Wyoming. The approximately 79,000-acre facility consists of the Cantonment Area, South 

Training Area (STA) and North Training Area (NTA). The Cantonment Area lies adjacent to the 

Town of Guernsey. The STA lies south and southwest of the Cantonment Area, while NTA is north 

of Guernsey State Park (AECOM Technical Services, Inc. [AECOM], 2020).

The four AOIs identified are within the Cantonment Area, which covers approximately 500 acres 

and contains facilities primarily for administrative, supply, and maintenance in support of training 

activities on Camp Guernsey. Facilities include, but are not limited to, training barracks, 

classrooms, warehouses, motor pools, maintenance facilities, a wastewater treatment plant, fuel 

storage, a heliport, and a paved airstrip/airfield. The Camp Guernsey Joint-Use Airfield, located 

in the eastern portion of the Cantonment Area and including the Camp Guernsey Army Airfield, is 

used by Camp Guernsey and the Town of Guernsey as their municipal/regional airport. 

The PA and SI QAPP Addendum identified four AOIs for investigation during the SI phase. SI 

sampling results from the four AOIs were compared to OSD SLs. Table ES-2 summarizes the SI 

results for each AOI. Based on the results of this SI, further evaluation under CERCLA is 

warranted in a Remedial Investigation (RI) for AOI 1 and AOI 4; no further evaluation is warranted 

for AOI 2 and AOI 3 at this time. 

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

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

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

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

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

individual chemical of concern in the absence of other PFAS.
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Table ES-1: Screening Levels (Soil and Groundwater) 

Analyteb

Residential

(Soil)

(μg/kg)a 

0-2 feet bgs

Industrial/ Commercial 

Composite Worker

(Soil)

(μg/kg)a 

2-15 feet bgs

Tap Water

(Groundwater)

(ng/L)a

PFOA 19 250 6

PFOS 13 160 4 

PFBS 1,900 25,000 601 

PFHxS 130 1,600 39

PFNA 19 250 6

Notes:

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

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

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

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

as an analyte at the time of this SI. Based on the CSM developed during the PA and revised based on SI findings, the presence of HFPODA is not anticipated at the facility because HFPO-DA is generally not a component of MIL-SPEC AFFF and based on its history including 

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

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

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

AOI Potential 

Release Area

Soil –

Source Area

Groundwater –

Source Area Future Action

1 Camp Guernsey Airfield Proceed to RI 

2 Current Firetruck

Maintenance Areas No further action

3 Historic Maintenance and 

Storage Areas No further action

4 Outdoor Wash Rack Proceed to RI

Legend:

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels
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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 Camp Guernsey in 

Guernsey, Wyoming. Camp Guernsey 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 Camp Guernsey (AECOM Technical Services, Inc. [AECOM], 2020) that

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

stored, disposed, or released historically. Additionally, during the development of the SI Quality 

Assurance Project Plan (QAPP) Addendum, an additional three AOIs were added (AECOM, 

2021), for a total of four AOIs. All four AOIs fall within the Cantonment area of Camp Guernsey. 

The objective of the SI is to identify whether there has been a release to the environment from 

the AOIs identified in the PA and during QAPP development 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

Camp Guernsey partially surrounds the towns of Guernsey and Hartville, in Platte County, 

Wyoming. The approximately 79,000-acre facility consists of the Cantonment Area, South 

Training Area (STA) and North Training Area (NTA). The Cantonment Area lies adjacent to the 

Town of Guernsey. The STA lies south and southwest of the Cantonment Area, while NTA is north 

of Guernsey State Park (Figure 2-1). The four AOIs were identified within the Cantonment Area.

The historic buildings in the Cantonment Area of Camp Guernsey were constructed in 1938 and 

1939 by the Works Projects Administration. The US Army leased 6,209 acres in 1943, during 

World War II, from the state of Wyoming (historically known as the STA). In 1944, approximately

4,500 acres of land within what is now Guernsey State Park were acquired from the Bureau of 

Land Management (BLM). Between 1943 and 1945, the US Army used the Camp Guernsey 

installation for bivouac and artillery maneuver training. In 1945, the lease with the US Army on 

the state land was terminated, and the buildings and improvements were transferred to the state 

of Wyoming. The 4,500 acres of former BLM land were declared excess by the Department of 

Defense in 1950 and returned to the Department of Interior. In 1951, the WYARNG took over 

management of the 6,209 acres of state property (Cantonment Area and STA). Through 1960, 

over 13,463 acres of land to the north were added to Camp Guernsey to establish an artillery 

range, impact area, and maneuver lands. These land acquisitions were completed through private 

land purchases and BLM patents (federal land withdrawals). Numerous private land acquisitions 

occurred from 2004 to 2012, adding 39,000 acres of land to the facility. These most recent 

acquisitions also encompassed an additional 3,000 acres of BLM land and 2,000 acres of State 

School Trust land.

The Cantonment Area covers approximately 500 acres and contains facilities primarily for 

administrative, supply, and maintenance in support of training activities on Camp Guernsey. 

Facilities include, but are not limited to, training barracks, classrooms, warehouses, motor pools,

maintenance facilities, a wastewater treatment plant, fuel storage, a heliport, and a paved 

airstrip/airfield. The Camp Guernsey Joint-Use Airfield, located in the eastern portion of the 

Cantonment Area, is used by Camp Guernsey and the Town of Guernsey as their 

municipal/regional airport. During a review of historical photographs, it was observed that the 

runway has been extended over the years. 

2.2 Facility Environmental Setting

Camp Guernsey lies within the High Plains section of the Great Plains physiographic province, 

near its western margin with the Rocky Mountains (US Geological Survey [USGS], 1960). The 

physiography of the NTA includes dissected plateaus, bluffs, and steep valley side-slopes. The 

physiography of the Cantonment and STA is much more subdued, given the proximity to the North 

Platte River. The STA is comprised primarily of irregular plains with moderate slope, and the 

Cantonment is situated on the floodplain and low plains adjacent to the North Platte River. The 

elevation at the Camp Guernsey Cantonment Area is between 4,300 and 4,400 feet above sea 

level. The Cantonment Area is mostly level, with slopes rising to the east towards the airfield.

Surface water drains to the south and southeast towards the North Platte River (Figure 2-2).

The Cantonment Area is roughly 25 percent (%) covered with developed and paved surfaces. The 

majority of the unimproved lands are open fields surrounding the airfield and adjacent to the North 

Platte River. The town of Guernsey abuts the Camp Guernsey facility boundary to the west and 

north. Properties immediately surrounding the Cantonment Area include single-family residential 

structures, schools, and other public or municipal facilities to the west-northwest; the Guernsey 
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BNSF Railyard, a cemetery, and industrial facilities to the north-northeast; and agricultural land 

and rural residential properties to the east-southeast. Undeveloped land, a golf course, and the 

STA are located across the North Platte River to the south. 

2.2.1 Geology

Camp Guernsey is roughly split into two geologic and geomorphic regimes. The NTA is located 

over Precambrian rocks exposed in the southwestern end of a fault known as the Hartville Uplift. 

The Hartville Uplift is a north-northeast trending structural arch (anticline) that separates the 

Denver Basin (to the southeast) from the Powder River Basin (to the northwest). The arch extends 

from the northeast end of the Laramie Range to the south end of the Black Hills, roughly 45 miles 

long and 15 miles wide - roughly between the communities of Glendo, Guernsey, Hartville, and 

Lusk. The Hartville Uplift has been subdued by erosion, with the current landscape showing little 

evidence of past tectonic activity. Along the anticline crest are exposed metavolcanic and granitic 

Precambrian age rocks surrounded by younger Pennsylvanian and Mississippian age 

sedimentary rocks of the Hartville Formation. The Hartville Uplift does not extend south of the 

North Platte River; however, a prominent ridge does run north to south down the middle of the 

STA (Wyoming ARNG [WYARNG], 2015). South of the North Platte River, the surface of Camp 

Guernsey is primarily mapped in Holocene sand and loess, as well as the Arikaree Formation of 

the Tertiary Period (Wyoming State Geological Survey [WSGS], 2005).

In the Cantonment Area, north of North Platte River, Camp Guernsey is mapped within Quaternary 

surficial deposits. Specifically, northwest of the river, the Cantonment Area is underlain by 

Holocene alluvial deposits consisting of silt, fine-grained sand, and some gravel. Northeast of the 

river, the Cantonment Area around the airfield is underlain by cemented Pleistocene gravel 

deposits consisting of boulder to pebble conglomerates. The Pleistocene gravel was deposited in 

a fluvial environment by the ancestral North Platte River. The Pleistocene gravel deposits occur 

as an upland deposit in the Guernsey and Guernsey Reservoir areas along the North Platte River

(WSGS, 2005). At the Cantonment, the transition between the two Quaternary deposits is visible 

from the ground surface by a relatively abrupt, approximately 60-foot elevation change between 

the lower elevation Holocene alluvial deposits and the terrace formed by the Pleistocene gravel 

fluvial deposits. However, this transition is less apparent in areas that have been graded for 

construction. The Arikaree Formation present in outcrops across the river at the STA is buried 

beneath the majority of the Cantonment. Only the upper unit of the Arikaree Formation is present 

in the area, which is characterized as a fine-grained, soft to moderately hard, generally massive,

tuffaceous sandstone (WSGS, 2005).

Hollow stem auger (HSA) soil borings were completed during the SI to depths ranging between 

5.5 to 50 feet below ground surface (bgs). At AOI 1, refusal was encountered in multiple borings

between 5.5 to 41 feet bgs, prior to encountering water bearing units. At nearby boring CG-01, 

associated with AOI 1, groundwater was encountered at approximately 40 feet bgs. Groundwater 

was encountered in borings at AOIs 2, 3, and 4 at depths between 25 to 50 feet bgs. The SI

borings encountered poorly graded sand with varying amounts of silt and gravel.

AOI 1 borings located atop the terrace near the airfield (AOI01-03 and AOI01-04) contained 

greater amounts of gravel than borings completed elsewhere during the SI. Additionally, these

two borings encountered refusal at a much shallower depth than other locations. These findings 

are consistent with the understood surficial geology at AOI 1 based on geologic maps that show 

these borings are located within the cemented gravel conglomerate. AOI 2 is mapped within the 

same gravel deposits; however, boring AOI02-01 contained predominantly finer-grained sandy 

deposits and did not hit refusal before groundwater. AOI 2 sits in a wide drainage basin, and the 

surface elevation of AOI02-01 was approximately 20 to 30 feet below the refusal elevations at 

AOI01-03 and AOI01-04. The lower elevation of AOI 2, in conjunction with the observed lithology, 
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indicates the resistant cemented gravel layer below AOI01-03 and AOI01-04 may have formerly

been present above AOI 2 but has since been eroded away. 

The observations made in the remainder of the SI borings show predominantly sandy deposits 

with varying amount of silt and some gravel, consistent with the Holocene alluvial deposits along 

the North Platte River floodplain. The underlying Arikaree Formation was not observed in SI 

borings.

Samples for grain size analyses were collected at two locations where finer grained deposits were 

observed, AOI01-01 (40 to 41 feet bgs) and AOI02-01 (30 to 32.5 feet bgs), and they were

analyzed via American Society for Testing and Materials (ASTM) Method D-422. The results 

indicate that the soil samples are comprised primarily of fine-grained sand (46.57% to 46.58%), 

silt (36.62% to 37.84%), and clay (9.14 to 12.63%). Boring logs are presented in Appendix E,

and grain size results are presented in Appendix F. The soils bordering the North Platte River 

are subject to periodic water saturation due to seasonal fluctuations in the water table and 

occasional flooding.

2.2.2 Hydrogeology

Four main aquifers underly the Guernsey area, including the alluvial aquifer, which is positioned

within the Quaternary alluvial deposits associated with the North Platte River and underlying the 

Cantonment. Deeper bedrock aquifers lie within the Arikaree, Guernsey, or the Hartville 

formations (URS, 2014). 

The alluvial aquifers tend to be located in valleys that contain sand and gravel deposits and are 

hydraulically connected to perennial streams that serve as sources of recharge. The alluvial 

aquifers in the Camp Guernsey area are heavily used for domestic and stock water production, 

as evidenced by the large number of wells located within the alluvial material limits (URS, 2014). 

The majority of the wells in the area draw water primarily from these alluvial aquifers. The largest 

alluvial aquifer in Wyoming is the alluvium along the North Platte River, which is used extensively 

for water storage, agricultural, municipal, industrial, and domestic water uses. Numerous bedrock 

aquifer wells installed in the Arikaree and Hartville formations are primarily used for domestic and 

livestock wells (URS, 2014).

Groundwater in the vicinity of Camp Guernsey was anticipated to be encountered at depths of 

approximately 40 feet bgs, and flow direction was anticipated to be predominantly southwest 

toward the North Platte River. In terrain such as that on Camp Guernsey, groundwater elevations 

tend to mimic the ground surface elevation. Therefore, groundwater elevations are generally 

greater in the highlands and lower in the lowlands. Because of the hydraulic connectivity between 

the groundwater and surface water in the alluvial aquifers, flow direction of the perennial water 

bodies, such as the North Platte River, often affects groundwater flow in the adjacent aquifers.

Synoptic groundwater level measurements collected during the SI were found to range between 

19.72 to 40.36 feet bgs. Groundwater elevations were calculated using depth to groundwater 

measurements and the surveyed ground surface elevation. Groundwater flow direction was 

observed to be generally to the southeast, consistent with the flow direction of the North Platte 

River (Figure 2-4).

Within the alluvial deposits, groundwater elevations were generally higher in the northwest

Cantonment and decreased towards the southeast. Where the alluvial deposits transition to 

Pleistocene gravel deposits near the airfield, groundwater was not encountered prior to drilling

refusal depths. On the terrace adjacent to the airfield, the absence of groundwater is likely a result 

of the limited storage capacity of the thin unconsolidated section atop cemented gravels. Thicker 

unconsolidated deposits were observed off the terrace at AOI01-01 and AOI01-02; however, 

groundwater was not observed prior to refusal. The refusal elevations in these borings were higher 

than the groundwater elevation in nearby boring CG-01, indicating that groundwater is likely 
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 2-4

present within 5 to 10 feet below the terminal borehole depths. Within the gravel deposits, 

groundwater was only encountered in one boring, AOI02-01, located in an apparent drainage 

basin that may have formed where the overlying cemented gravel has eroded away. The

groundwater elevation at AOI 2 was nearly 20 feet higher than in the other SI boring locations, 

suggesting the resistant unit observed at AOI 1 may act as a local shallow groundwater divide

and separates this basin hydraulically from the Cantonment area west the airfield. The 

groundwater flow direction at AOI 2 is assumed to follow the south-southeast trace of the drainage 

basin, consistent with the overall flow direction for the investigation area.

Groundwater is the primary source of drinking water for the town of Guernsey, Camp Guernsey, 

and surrounding residential areas outside of the town limits (US Army Center for Health Promotion 

and Preventative Medicine [USACHPPM], 2001). The town of Guernsey is located within the Town 

of Guernsey Wellhead Protection Area and has several drinking water supply wells in operation 

that produce 220 million gallons per year (USACHPPM, 2003). Camp Guernsey also has drinking 

water supply wells that lie in the same alluvial gravel layer as the wells for the town of Guernsey. 

Numerous other potable wells are located within a 4-mile radius of the Cantonment (WSGS, 

2019). The identified downgradient domestic wells are located across the North Platte River.

Groundwater features are presented on Figure 2-3.

At Camp Guernsey, sampling was completed for eight drinking water sources and one blended 

water sample location prior to the entry point of the distribution system (Tetra Tech, Inc., 2017).

On 15 May 2017, the water samples were collected from various spigots associated with the 

Camp Guernsey drinking water sources. The samples were analyzed for a subset of 18 

compounds by USEPA Method 537 modified. These compounds include the relevant compounds 

(PFOA, PFOS, PFBS, PFHxS, and PFNA). PFOA was detected at a concentration of 0.753 JM 

nanograms per liter (ng/L) in a drinking water sample sourced from a location in the SI 

investigation area. No other detections of the relevant compounds were reported from single 

drinking water sources or the blended water sample location (Tetra Tech, Inc., 2017). In 2021, 

WYARNG collected an additional drinking water sample from a single location on the airfield for 

analysis of a subset of 18 compounds, including all relevant compounds, by USEPA Method 

537.1. Results from the 2021 sample were non-detect for all compounds analyzed. 

2.2.3 Hydrology

Camp Guernsey falls within the lower drainage of the North Platte River, a braided channel that

flows through parts of the NTA from the northwest to the southeast. The Cantonment is 

immediately north of the North Platte River. Stormwater runoff over much of Camp Guernsey is 

conveyed overland by surface drainages and eventually discharges to the river. Wastewater 

captured by floor drains flows to the sanitary sewer, in some locations through an oil-water 

separator (OWS), and is then treated at the Town of Guernsey’s permitted wastewater treatment 

facility located on Camp Guernsey. The treatment facility, operated by the Town of Guernsey on

land leased from WYARNG, consists of several lined, aeration lagoons and a polishing lagoon

located along the southern portion of the Cantonment Area, immediately north of the river. Treated 

wastewater is discharged from the facility to the North Platte River during part of the year, typically 

the summer months. In the winter, wastewater discharge is diverted to two infiltration basins 

located immediately adjacent to the treatment facility. Based on information provided by 

WYARNG, sludge was removed the ponds in the 1970s and around 1990; however, the 

disposition of the recovered sludge, whether on-facility or off-facility, is not known at this time. 

Surface water features are presented on Figure 2-5.

The width of the North Platte River channel in this area is approximately 300 feet, with a typical 

centerline depth ranging from 0 to 8 feet depending on discharges from the Glendo and Guernsey 

Reservoirs (WYARNG, 2015). Water depths and flow rates are variable from season to season.

Discharge from the Guernsey Reservoir to the North Platte River is typically limited to a short, 
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 2-5

several week period during the summer to flush silt from the reservoir and maintain downstream 

irrigation reserves. The average annual flow is approximately 1,000 cubic feet per second (cfs), 

with extremes ranging from as low as 0 cfs during times of low flow (November through March) 

to a maximum of up to 30,000 cfs during times of extreme precipitation or reservoir drainage (late 

June and early July). The North Platte River is primarily used for water transport for agricultural 

uses (USACHPPM, 2003). The river also serves as a valuable fishery upstream from Camp 

Guernsey; however, it is not recognized as such in the stretch near the Cantonment, based on 

information received from WYARNG. A popular activity for Guernsey residents is to float the North

Platte River on inner tubes.

2.2.4 Climate

The climate of east-central Wyoming is a dry, mid-latitude, steppe climate, and it is characterized 

by cold winters, hot summers, and low humidity (Commission for Environmental Cooperation, 

2011). Wheatland, the county seat of Platte County, is less than 10 miles southwest of the facility. 

The average temperature in Wheatland is 49.55 degrees Fahrenheit (°F). In winter, average low 

temperatures reach a minimum of 18°F. In summer, the average high temperatures reach a 

maximum of 89°F. The area receives an average of 13.7 inches of rain and 37 inches of snow per 

year (World Climate, 2022).

2.2.5 Current and Future Land Use

Camp Guernsey is a National Guard Bureau Level 2 Joint Training Center that exists to facilitate 

and support realistic combat training for current and future American fighting forces (WYARNG, 

2021). Camp Guernsey can be divided into four distinct training areas:

• NTA – 51,000 acres of live fire and maneuver areas, north of Guernsey State Park;

• STA – various training ranges, south and southwest of the Cantonment Area;

• Camp Guernsey Army Airfield – airfield for rotary and fixed wing aircraft with crash fire 

rescue capability, located within the Cantonment and used by Camp Guernsey and the 

Town of Guernsey as their municipal/regional airport; and

• Cantonment – Dining facility and billeting, east of the Town of Guernsey.

Numerous residential, commercial, and recreational structures are located to the west/northwest 

of the Cantonment Area. Industrial use properties, including a BNSF Railyard, are located 

immediately north and northeast of the facility. The Platte River and a golf course are located to 

the south of the Cantonment Area. Reasonably anticipated future land use is not expected to 

change from the current land use described above. 

2.2.6 Sensitive Habitat and Threatened/ Endangered Species 

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

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

Service [USFWS], 2022).

• Birds: Whooping crane, Grus americana (endangered); Piping Plover, Charadrius melodus

(threatened)

• Flowering Plants: Western prairie fringed Orchid, Platanthera praeclara (threatened); Ute 

ladies'-tresses, Spiranthes diluvialis (threatened)
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 2-6

• Insects: Monarch butterfly, Danaus plexippus (candidate); Regal fritillary, Speyeria idalia

(under review)

• Mammals: Tricolored bat, Perimyotis subflavus (proposed endangered); Little brown bat, 

Myotis lucifugus (under review); Preble's meadow jumping mouse, Zapus hudsonius preblei

(threatened); Gray wolf, Canis lupus (under review)

2.3 History of PFAS Use

Four AOIs were identified in the PA and SI QAPP Addendum where AFFF may have been used, 

stored, disposed, or released historically at Camp Guernsey (AECOM, 2020 and AECOM, 2021).

These AOIs include:

• AOI 1: Camp Guernsey Airfield: Every 2 years between approximately 1990 to 2004, 

fire training activities occurred at the Camp Guernsey Airfield. AFFF was reportedly 

released during these events. Aerial imagery provided by WYARNG suggests additional 

fire training activities or other releases of AFFF have occurred as recently as 2013. In

addition, AFFF is stored in bulk containers and in firefighting equipment within a 

warehouse next to the Airfield Operations. 

• AOI 2: Current Firetruck Maintenance Areas: From 2001 to present, firetruck

maintenance has been completed at the current Unit Training Equipment Site (UTES), 

Combined Support Maintenance Shop (CSMS), and Field Maintenance Shop (FMS) 

#5. No documented releases have occurred at AOI 2, as it is unknown if AFFF were

stored in the firetrucks during maintenance. 

• AOI 3: Historic Maintenance and Storage Areas: Prior to 2001, firetruck storage and/or 

maintenance occurred at five areas on the west side of the Cantonment: Building #11, 

Building #106, Building #603, Building #16-FROG, and the Cold Storage building. There 

are no documented releases at AOI 3.

• AOI 4: Outdoor Wash Rack: At the outdoor wash rack, firetruck washing was observed 

at least once since 2009. There are no documented releases at AOI 4.
Camp Guernsey Cantonment

­12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

AG

1/25/2023

1/25/2023

PROJECT Site Inspection at Camp Guernsey, WY

1/25/2023

1:316,800

PM CM 1/25/2023 Base Map: Sources: Esri, HERE, Garmin, USGS,

Intermap, INCREMENT P, NRCan, Esri Japan, METI,

Figure 2-1

Facility Location

Legend

Facility Boundary

0 2.5 5 10

Miles

AECOM 2-7
­12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

AG

3/3/2023

3/3/2023

PROJECT Site Inspection at Camp Guernsey, WY

3/3/2023

1:24,000

PM CM 3/3/2023 Base Map: USGS The National Map: National

Boundaries Dataset, 3DEP Elevation Program,

Figure 2-2

Facility Topography

Legend

Facility Boundary

0 1,000 2,000 4,000

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AECOM 2-8
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Camp Guernsey

Cantonment

­12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

AG

3/6/2023

3/6/2023

PROJECT Site Inspection at Camp Guernsey, WY

3/6/2023

1:190,080

PM CM 3/6/2023 Base Map: Sources: Esri, HERE, Garmin, USGS,

Intermap, INCREMENT P, NRCan, Esri Japan, METI,

Figure 2-3

Groundwater Features

Legend

Facility Boundary

Water Body

Wetland

Inferred Groundwater Flow

Direction

Groundwater Flow Direction

Geology

alluvium

conglomerate

dune sand

fine-grained mixed clastic

granitoid

limestone

metasedimentary rock

mudstone

sandstone

shale

siltstone

unconsolidated deposit

Well

!P Domestic

!5 Industrial

!5 Irrigation

!5 Stock

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A! Monitoring

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0 1.5 3 6

Miles

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AECOM 2-9
!?

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!?

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!?

North Platte River

AOI02-01

4325.64

AOI03-01

4308.19

AOI03-02

4308.13

AOI03-03

N/A

AOI03-04

4308.91

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4306.63

CG-01

4308.68

4307

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4307

4308

4308

4306

4309

4309

­12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

AD

3/3/2023

3/3/2023

PROJECT Site Inspection at Camp Guernsey, WY

3/3/2023

1:10,800

PM CM 3/3/2023 Base Map: Sources: Esri, HERE, Garmin, USGS,

Intermap, INCREMENT P, NRCan, Esri Japan, METI,

Figure 2-4

Groundwater Elevations,

May 2022

Legend

!? Soil Boring/Groundwater Sampling Point

Facility Boundary

Water Body

Groundwater Elevation Contour

Inferred Groundwater Elevation Contour

Groundwater Flow Direction

Inferred Groundwater Flow Direction

0 450 900 1,800

Feet

Groundwater elevations in ft NAVD88.

N/A = not available, location not surveyed.

AECOM 2-10
Camp Guernsey 

Cantonment

Middle

Broom Creek

Watershed

Lower

Broom Creek

Watershed

Lower Horseshoe

Creek Watershed

Lower Cottonwood

Creek Watershed

Porter Rock

Watershed

Upper Broom

Creek Watershed

North Bear

Creek-North Platte

River Watershed

Middle

Bear Creek

Watershed

Little Cottonwood

Creek-North Platte River

Watershed

Guernsey

Reservoir-North Platte

River Watershed

Guernsey Fish

Pond-North Platte

River Watershed

Whalen

Canyon

Watershed

Cottonwood Creek

Watershed

Grayrocks

Reservoir-Laramie

River Watershed

Reservoir

Number 3-Laramie

River Watershed

Big Draw-North

Laramie River

Watershed

Fish Creek

Watershed

Dwyer

Cemetery

Watershed

Sixmile

Creek-Laramie

River Watershed

Deer Creek

Watershed

­12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

MC

3/3/2023

3/3/2023

PROJECT Site Inspection at Camp Guernsey, WY

3/3/2023

1:190,080

PM CM 3/3/2023 Base Map: Sources: Esri, HERE, Garmin, USGS,

Intermap, INCREMENT P, NRCan, Esri Japan, METI,

Figure 2-5

Surface Water Features

Legend

Facility Boundary

Water Body

Wetland

DamWeir

Gate

Lock Chamber

Nonearthen Shore

Surface Water Flow Direction

0 1.5 3 6

Miles

AECOM 2-11
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 2-12

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3. Summary of Areas of Interest 

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

disposed, or released historically. The PA originally identified only AOI 1: Camp Guernsey Airfield 

as a potential release area. However, the ARNG G-9 subsequently adopted a more conservative 

approach that identified any AFFF storage area, whether a known release occurred or not, as a 

potential release area. Based on the PA and evolving approach during the SI QAPP development, 

twelve potential release areas were identified at Camp Guernsey and grouped into four AOIs

(AECOM, 2020 and AECOM, 2021). The potential release areas are shown on Figure 3-1.

No off-facility sources adjacent to Camp Guernsey were identified during the PA (AECOM, 2020). 

However, as the widespread nature of the use of PFAS-containing materials becomes better 

understood, other areas not previously identified, both on- and off-facility, may be considered. The 

former Town of Guernsey landfill is located less than 1-mile to the northwest of the Camp 

Guernsey Cantonment and is likely connected hydrogeologically to the alluvial deposits beneath 

Camp Guernsey (Wyoming Department of Environmental Quality [WYDEQ], 2017). Landfills are 

not usually a primary source of PFAS; however, PFAS-containing materials disposed of in landfills 

may leach the compounds into the environment over time. The Town of Guernsey landfill was in 

operation from the 1950s until it closed in 1999. In addition to waste from Camp Guernsey, the 

landfill received wastes from municipal, industrial, and other sources. There are no confirmed 

releases or disposals of PFAS-containing materials at the landfill; however, records of the type 

and management of waste disposed at the facility are unavailable for most of the history of the 

landfill because access was unrestricted and landfill operations were unmonitored before 1987 

(USACHPPM, 2001). The Town of Guernsey currently operates a yard waste disposal area 

immediately north of the former landfill. According to WYARNG, the yard waste at this location is 

managed through periodic burns during which the Camp Guernsey fire department must be 

present. It is not known whether Camp Guernsey personnel have ever used foam at this location.

The locations of the landfill and yard waste area are shown in Figure 3-1 for informational 

purposes but were not evaluated as part of this SI.

3.1 AOI 1 Camp Guernsey Airfield

AOI 1 is the Camp Guernsey Airfield. Located on Bridger Avenue, the Camp Guernsey Airfield 

includes multiple buildings, a landing strip, and taxiway. The Camp Guernsey Airfield and the 

Guernsey Municipal Airport is a Joint Use Airfield.

Firetrucks are generally stationed at Fire House #1 (Building #107), which is co-located at the air 

traffic control tower, or at the fire station parking annex, adjacent to the large aircraft parking 

apron. The fire house was built in 1988 and has been used to store firetrucks and maintain stateowned firetrucks since that time. Firetrucks were also cleaned periodically in the fire house, and 

wastewater generated from these activities reportedly drained to an oil water separator. The oil 

water separator has an 8,000-gallon containment tank that is pumped and disposed offsite. 

Wastewater is treated at the Town of Guernsey wastewater treatment facility located on the Camp 

Guernsey Cantonment.

According to an interview in 2016 with the former Camp Guernsey Fire Chief, the fire department 

trained with AFFF every 2 years on the airfield, as the AFFF expired every 2 years. The training

occurred approximately five times in the 1990s. In 2004, Camp Guernsey ceased this operation 

when the current Camp Guernsey Fire Chief arrived. The specific location of the events was 

unknown; however, AFFF was reportedly used exclusively at the airfield. The type, amount, and 

concentration of AFFF used during the training activities are also unknown. Additionally, it is 

unknown if all three firetrucks were used every event and how the AFFF was released during the 

training events. The information from the former Camp Guernsey Fire Chief and the period of his 
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AECOM 3-2

service cannot be corroborated, nor can additional details be gathered, as the interviewee passed 

away after the 2016 interview, and no records were found regarding the concentration or amount 

of AFFF used for training in the 1990s. Aerial imagery dated from 2013 was provided by WYARNG 

after SI field activities were completed and shows what appears to be foam and wet pavement at 

the south end of the airfield, suggesting additional fire training or other release of AFFF may have 

occurred at AOI 1 as recently as 2013. 

In addition, AFFF is stored within a warehouse next to the Airfield Operations. At the time of the 

PA, AFFF was stored in eight 55-gallon drums (6% concentration) and in four Airport Rescue 

Firefighter vehicles; one Airport Rescue Firefighter vehicle has a 160-gallon tank, and three have 

380-gallon tanks. Aircraft are re-fueled on the aircraft parking aprons with a 5,000-gallon fuel 

truck. Fire extinguishers with Purple-K are also co-located on the parking aprons and on the fuel 

truck. Information provided by WYARNG since SI field activities indicates that bulk AFFF is stored 

in thirteen (13) 55-gallon drums and six 5-gallon containers.

The airfield ramp is gently sloped with an apex occurring in the middle. Access roads, including 

Bridger Avenue, which ends at Fire House #1, climb the terrace from the west side of the airfield. 

Several stormwater infiltration basins are located to the south and east of the airfield, and the 

Platte River is located to the south. Releases at AOI 1 may have occurred directly onto surface 

soil or pavement but may also have infiltrated to the subsurface soil via runoff, cracks in pavement,

or joints between areas that are paved with different materials. The access roads leading up from 

the Cantonment to the west side of the airfield may convey runoff downslope during heavy 

precipitation events. Releases in buildings and nearby on parts of the airfield would drain to floor 

drains. These drains would convey AFFF with wastewater to the sanitary sewer and then to the 

wastewater treatment facility located on Camp Guernsey. 

3.2 AOI 2 Current Firetruck Maintenance Areas

AOI 2 comprises an area east of the runway where firetruck maintenance is reported to occur and 

includes the current UTES, CSMS, and FMS #5. Federally owned firetrucks are maintained on 

Camp Guernsey at either the UTES or CSMS. State-owned vehicles are maintained either at FMS 

#5, Camp Guernsey fire station by either ARNG mechanics or contracted mechanics, or the 

vehicle is taken off-facility to a commercial maintenance shop.

The UTES, CSMS, and FMS #5 buildings were constructed in 2001 and have been the site of 

firetruck maintenance since that time. In addition, firetrucks may have used the interior wash racks 

within the CSMS and FMS #5 buildings. It is unknown if AFFF were in the firetrucks during 

maintenance, if AFFF were potentially released during maintenance, and if firetrucks cleaned at 

the wash rack had residual AFFF on the exterior of the trucks. During the PA, interviewees 

indicated that the firetrucks were cleaned periodically, and wastewater generated from these 

activities went to the oil water separator, which discharges to the sanitary sewer and then flows 

to the wastewater treatment facility. 

All firetruck maintenance and washing occurred inside the building; however, due to the potential 

for undocumented releases of AFFF, the area was conservatively added as an AOI. Any AFFF 

releases would have occurred on paved/concrete areas. AFFF released to the pavement or 

concrete could have infiltrated subsurface soil via cracks in pavement/concrete or joints between 

areas that are paved with different materials.

3.3 AOI 3 Historic Maintenance and Storage Areas

AOI 3 includes five areas on the west side of the Cantonment where firetruck maintenance and/or 

AFFF storage were known to occur: Building #11, Building #106, Building #603, Building #16-

FROG, and the Cold Storage building.
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AECOM 3-3

Building #11 is located along the northern boundary of AOI 3 and operated as the CSMS prior to 

2001. It is assumed that firetruck maintenance was conducted in this building. In addition, a truck 

wash sump is located within the building. 

Building #106 is located along the eastern boundary of AOI 3 and operated as the UTES prior to 

2001. It is assumed that firetruck maintenance was conducted in this building, and the building is 

currently a training center with classrooms. 

Building #603 is located along the eastern boundary of AOI 3, south of Building #106. Building 

#16-FROG is located in the southern portion of AOI 3. Buildings #603 and #16-FROG were used 

to store firetrucks before 1988. In addition, the fire department has stored firetrucks in both 

buildings during the winter in recent years.

The Cold Storage building is located on the western boundary of AOI 3. This building may have 

stored firetrucks here prior to 1988. 

There are no documented releases at these five areas; however, due to the potential for 

undocumented releases of AFFF in the buildings, the locations were conservatively added as an 

AOI. Any AFFF releases would have occurred on paved/concrete areas. AFFF released to the 

pavement or concrete could have runoff to unpaved areas or infiltrated subsurface soil via cracks 

in pavement/concrete or in joints between areas that are paved with different materials. Releases 

in buildings or wash facilities may drain with wastewater to the sanitary sewer and then flow to 

the wastewater treatment facility.

3.4 AOI 4 Outdoor Wash Rack

AOI 4 comprises the outdoor wash rack west of the airfield. Firetrucks are not permitted to be 

washed in the outdoor wash rack area; however, firetrucks were observed being washed there at 

least once since 2009. Based on the potential for undocumented releases, the area was 

conservatively added as an AOI. Releases at AOI 4 may have occurred directly onto surface soil 

or pavement but may also have infiltrated to the subsurface soil via cracks in pavement or joints 

between areas that are paved with different materials. Releases captured by the wash rack drain 

would convey to the sanitary sewer and then flow to the wastewater treatment facility.
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AECOM 4-1

4. Project Data Quality Objectives

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

Addendum (AECOM, 2021), the objective of the SI is to identify whether there has been a release 

to the environment at the AOIs identified in the PA and SI QAPP Addendum. For each AOI, ARNG 

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

threats, or whether no further action is warranted. This SI evaluated groundwater and soil for 

presence or absence of relevant compounds at each of the sampled AOIs.

4.1 Problem Statement

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

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

SLs are presented in Section 6.1 of this report.

4.2 Information Inputs

Primary information inputs included:

• The PA for Camp Guernsey (AECOM, 2020);

• Analytical data collected as part of ARNG drinking water sampling efforts around the facility 

(Tetra Tech, Inc., 2017);

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

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

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

parameters measured at the time of sampling.

4.3 Study Boundaries

The scope of the SI was bounded by the property limits of the facility (Figure 2-2). 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). The SI scope was bounded vertically by the depth of groundwater and HSA drilling refusal. 

Temporal boundaries were limited to the spring 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, 2021). Pace Gulf Coast performed the following 

methods listed on their certifications: PFAS by PFAS by LCMSMS Compliant with QSM 5.3 Table 

B-15, TOC by SW-846 EPA 9060A, and pH by 9045D.

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 
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AECOM 4-2

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 

facility-specific DQOs. Both sampling and analytical activities are considered to assess whether 

the collected data are of the right type, quality, and quantity to support the decision-making (DoD, 

2019a; DoD, 2019b; USEPA, 2017).

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

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

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

requirements of the SI QAPP Addendum (AECOM, 2021).
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Camp Guernsey, Wyoming

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, Camp Guernsey, Guernsey, Wyoming dated March

2020 (AECOM, 2020);

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

Camp Guernsey, Guernsey, Wyoming dated November 2021 (AECOM, 2021); and

• Final Site Safety and Health Plan, Camp Guernsey, Guernsey, Wyoming dated May 2022

(AECOM, 2022).

The SI field activities were conducted from 9 March, 21 April to 6 May, and 3 June 2022 and 

consisted of decontamination source water sample collection, utility clearance, HSA borings, soil 

sample collection, groundwater sampling point installation, low-flow groundwater sample collection, 

and land surveying. Field activities were conducted in accordance with the SI QAPP Addendum 

(AECOM, 2021), except as noted in Section 5.8. 

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

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

Systems Manual (QSM) 5.3 Table B-15 to fulfill the project DQOs:

• Fifty-one (51) soil samples from thirty-one (31) locations;

• Seven (7) low-flow groundwater samples from seven (7) permanent groundwater sampling

points; and

• Twenty-seven (27) quality assurance (QA)/quality control (QC) samples.

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

list of samples collected for each media. Field documentation is provided in Appendix B. A Log 

of Daily Notice of Field Activity was completed throughout the SI field activities, which is provided 

in Appendix B1. Sampling forms are provided in Appendix B2, Field Change Request forms are

provided in Appendix B3, Nonconformance and Corrective Action Reports (NCRs) are provided 

in Appendix B4, land survey data are provided in Appendix B5, and investigation-derived waste 

(IDW) polygons are provided in Appendix B6. 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.) 
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Camp Guernsey, Wyoming

determining data needs; 3.) developing data collection strategies; and 4.) finalizing the data 

collection plan. The process encourages stakeholder involvement in the SI, beginning with 

defining overall project objectives, including DQOs, and formulating a sampling approach to 

address the AOIs identified in the PA and SI QAPP Addendum. 

A combined TPP Meeting 1 and 2 was held on 27 May 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, WYARNG, USACE, and WYDEQ. Stakeholders were 

provided the opportunity to make comments on the technical sampling approach and methods at 

the combined TPP Meeting 1 and 2. The outcome of the combined TPP Meeting 1 and 2 was 

memorialized in the SI QAPP Addendum (AECOM, 2021). 

A TPP Meeting 3 was held on 25 May 2023 to 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 

Both AECOM and their drilling contractor, Cascade Technical Services, LLC, contacted One Call 

of Wyoming (Wyoming 811), the utility clearance contractor, prior to mobilization to notify them of 

intrusive work. Because Wyoming 811 locators do not locate private utilities, such as those 

belonging to Camp Guernsey, AECOM contracted Ground Penetrating Radar Systems, LLC. 

(GPRS) to perform utility clearance for private utilities at all boring locations. GPRS performed the 

utility clearance under the oversight of the AECOM field team on 21 and 22 April 2022 using

industry standard methods in addition to ground-penetrating radar. Additionally, the first 5 feet of 

the direct-push borings were advanced using hand augering methods to visually verify utility 

clearance in the shallow subsurface where utilities would typically be encountered. 

5.1.3 Source Water and Sampling Equipment Acceptability

One potable water source at Camp Guernsey was sampled on 9 March 2022 to assess usability 

for decontamination of drilling equipment. Results of the sample collected (CG-DECON03092022) confirmed this source to be acceptable for use in this investigation; therefore, it was 

used throughout the field activities. An additional decontamination water source sample (CG-PW1) was collected on 2 May 2022 from the same source water after it passed through the drillers

equipment and confirmed the source’s usability. Specifically, the samples were analyzed by

LC/MS/MS compliant with QSM 5.3 Table B-15, and usability was defined as source water

concentrations less than or equal to 1/5 SL for any relevant compound. The results of the

decontamination water samples associated with the source used during the SI are provided in

Appendix F. A discussion of the results is presented in the DUA (Appendix A).

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

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

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

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

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

regarding the allowable materials within the sampling environment. 

5.2 Soil Borings and Soil Sampling

Soil samples were collected via HSA methods, in accordance with the SI QAPP Addendum 

(AECOM, 2021). A Mobile Drill B59 split spoon sampling system was used to collect soil cores to 

the target depth. A hand auger was used to collect soil from the top 5 feet of the boring, in 

accordance with AECOM utility clearance procedures. The soil boring locations are shown on 
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Figure 5-1, and depths are provided Table 5-1. Several boring locations were relocated for 

reasons including drill rig access, utility avoidance, and difficult lithology, as indicated in Section 

5.8.

In general, three discrete soil samples were collected from the vadose zone for chemical analysis 

from each HSA soil boring: one surface soil sample (0 to 2 feet bgs), one subsurface soil sample 

approximately 1 foot above the observed groundwater table, and one subsurface soil sample at 

the mid-point between the surface and the groundwater table. Due to early refusal or recovery 

limitations, two discrete soil samples were collected at borings AOI01-03, AOI01-04, AOI01-18, 

AOI01-19, AOI03-01, and AOI03-02. To supplement the drilled boring locations, additional surface 

soil samples were collected at other locations using a hand auger.

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

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

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

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

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

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

HSA soil borings were completed during the SI to depths ranging between 5.5 to 50 feet bgs. At 

AOI 1, refusal was encountered between 5.5 to 41 feet bgs at all HSA borings, prior to 

encountering water bearing units. Groundwater was encountered in borings at AOI 2, 3, and 4 at 

depths between 25 to 50 feet bgs. The SI borings encountered poorly graded sand with varying 

quantities of silt and gravel. Higher amounts of gravel were observed in borings on top of the 

terrace, near the airfield, where only a thin section of unconsolidated deposits was present before 

refusal was encountered 6- to 10-feet bgs in the underlying cemented gravel conglomerate. 

Refusal encountered at other locations not on this terrace was likely the result of large cobbles or 

boulders present within the alluvium. These findings are consistent with the understood surficial 

geology within the Cantonment as noted in Section 2.2.1.

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 by LC/MS/MS compliant with QSM 5.3 Table B-15, total organic 

carbon (TOC) (USEPA Method 9060A), pH (USEPA Method 9045D), and grain size (ASTM 

Method D-422) in accordance with the SI QAPP Addendum (AECOM, 2021).

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

as the accompanying samples. Matrix spike/matrix spike duplicates (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.

HSA borings were installed in unpaved areas, where able, to avoid disturbing concrete or asphalt 

surfaces. Where groundwater was encountered, HSA borings were converted to permanent 

groundwater sampling points, in accordance with the SI QAPP Addendum (AECOM, 2021). 
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5.3 Permanent Groundwater Sampling Point Installation and 

Groundwater Sampling

During the SI, seven permanent groundwater sampling points were installed at or downgradient 

of potential source areas. The locations of the sample points are shown on Figure 5-1. 

A Mobile Drill B59 drill rig was used to install seven 2-inch diameter groundwater sampling points. 

The groundwater sampling points were constructed with Schedule 40 PVC, flush threaded 10-

foot sections of riser, 0.010-inch slotted screen, and a threaded bottom cap. The target screen 

interval for each location was the top of the groundwater table. A filter pack of 10/20 silica sand 

was installed in the annulus around the screen to a minimum of 2 feet above the screen. 

A 2-foot-thick bentonite seal was placed above the filter sand and hydrated with potable water. 

Bentonite chips were then placed in the borehole annulus from the top of the bentonite seal to 6

inches bgs. The remaining space was filled with concrete to just below the ground surface. The 

sample points were allowed to set for at least 24 hours prior to development in accordance with 

the SI QAPP Addendum (AECOM, 2021). All groundwater sampling points were completed at the 

surface with a sealing gripper cap and flush mount vault with bolt-down lids. The screen interval 

of each of the groundwater sample points is provided in Table 5-2.

Development and sampling of points were completed in accordance with the SI QAPP Addendum 

(AECOM, 2021). The newly installed groundwater sampling points were developed no sooner 

than 24 hours following installation by pumping and surging using a variable speed submersible 

pump. Samples were collected no sooner than 24 hours following development via low-flow 

sampling methods using a Geotech Geosub 2 bladder pump with disposable PFAS-free, HDPE 

tubing. New tubing was used at each sampling point, and the pumps were decontaminated 

between each location. The sample points were 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 oxidation-reduction 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 any of the groundwater samples.

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

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

standard CoC procedures to the laboratory and analyzed by LC/MS/MS compliant with QSM 5.3 

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

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. Because non-dedicated sampling equipment 

was required due to the use of a bladder pump, equipment rinsate blanks were collected at a rate 

of 5% and analyzed for the same parameters as the groundwater 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 5 May 2022. Groundwater elevation 

measurements were collected from the seven new permanent groundwater sampling points. 

Water level measurements were taken from the northern side of the sample point casing. Depths 

to water measured at the permanent groundwater sampling points ranged from 19.72 to 40.36

feet bgs. A groundwater flow contour map is provided in Figure 2-4. Groundwater elevation data 

are provided in Table 5-3.
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5.5 Surveying

The northern side of each groundwater sampling point casing was surveyed by Wyoming-licensed 

land surveyors following guidelines provided in the SOPs provided in the SI QAPP Addendum 

(AECOM, 2021) except as noted in Section 5.8. Survey data from the newly installed points on 

the facility were collected on 3 June 2022 in the Wyoming State Plane Coordinates East Zone 

1983 North American Datum (2011) (horizontal) and North American Vertical Datum 1988 

(vertical). The surveyed groundwater sampling point data are provided in Appendix B5.

5.6 Investigation-Derived Waste

As of the date of this report, the disposal of IDW is not regulated federally. IDW generated during 

the SI is considered non-hazardous waste and was managed in accordance with the SI QAPP 

Addendum (AECOM, 2021) and with the DA Guidance for Addressing Releases of PFAS, Q18 (DA, 

2018).

Non-hazardous solid IDW (i.e., soil cuttings) generated during SI activities was left in place at the 

point of the source. The soil cuttings were distributed on the downgradient side of the borehole. 

The IDW was not sampled and assumes the PFAS characteristics of the associated soil samples 

collected from that source location.

Liquid IDW generated during SI activities (i.e., purge water and decontamination fluids) was

discharged directly to the ground surface slightly downgradient of the source of generation in 

accordance with USEPA Management of IDW (USEPA, 2014). This IDW was not sampled and 

assumes the characteristics of the associated groundwater samples collected from that source 

location. 

Geographic coordinates were collected using a global Positioning System (GPS) around each 

location where IDW was placed (i.e., an IDW polygon). The IDW polygons are displayed on the 

figure in Appendix B6.

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

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.

5.8 Deviations from SI QAPP Addendum

Three deviations from the SI QAPP Addendum were identified during review of the field 

documentation. The deviations are noted below and is documented in Field Change Request 

(FCR) Forms (Appendix B3) and an NCR (Appendix B4): 

• Multiple sample locations were relocated due to the presence of utilities or subsurface 

conditions encountered. The original surface soil location AOI02-03 was found to be in

concrete, so a new sample location was offset 50 feet north. During the hand clearance of 

boring location AOI01-01, concrete refusal was hit at 2.5 feet, and so the boring location 

was relocated over 100 feet west of the original location. During the utility locate at boring 

location AOI01-02, it was determined that the terrain in the area was not conducive for the 

rig to safely access; therefore, the sample location was relocated approximately 100 feet 
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 5-6

west. A new surface soil sample (AOI01-17) was proposed to sample the potential fire 

station release area where AOI01-02 was originally located. These actions were 

documented in FCR001 provided in Appendix B3. 

• During the drilling activities at AOI 1, refusal was encountered at all four boring locations

due to the geology near the airfield. There were no additional areas to step out to the east

or west at the revised boring locations for AOI01-01 and AOI01-02 (as discussed in

FCR001). Per discussions with ARNG and USACE, two additional boring locations were

completed downgradient of AOI 1 (AOI01-18 and AOI01-19) in an effort to collect

groundwater samples. The additional boring locations were placed off the terrace in

locations approved by ARNG, USACE, and WYARNG. This action was documented in

FCR002 provided in Appendix B3. Both relocated borings encountered refusal prior to

groundwater.

• Upon review of the groundwater sampling point survey data provided by the subcontracted

licensed surveyor, it was found that data for one permanent groundwater sampling point

(AOI03-03) were not recorded. The remaining groundwater sampling points were correctly

surveyed, and the measured water level data were used to develop the groundwater

elevation contour. The groundwater flow direction DQO was met using the available data

and suggests a southeast flow direction. This action was documented in NCR001 provided

in Appendix B4.

• During HSA drilling activities, the mid-point subsurface soil sample was collected from 15 to

20 feet bgs at boring AOI03-04 (AOI03-04-SB-15-20). The approved SI QAPP Addendum

states that mid-point subsurface soil samples would be collected from 13 to 15 feet bgs if

depth to water were greater than 30 feet bgs. Water was encountered at approximately 32

feet bgs during drilling, and the mid-point samples were inadvertently collected at depths

greater than 15 feet bgs. Mid-point soil samples were correctly collected at AOI 3 at three

boring locations (AOI03-01, AOI03-02, and AOI03-03). Consequently, the analytical results

of the mid-point sample collected at AOI03-04 (15 to 20 feet bgs), as well as the correctly

collected mid-point soil samples at AOI 3, were used to make conservative assumptions for

the CSM. This action was documented in NCR002 provided in Appendix B4.
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, Camp Guernsey, Guernsey, Wyoming

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) Comments

AOI01-01-SB-(0-2) 4/29/2022 1405 0 - 2 x

AOI01-01-SB-(0-2)-D 4/29/2022 1405 0 - 2 x Duplicate

AOI01-01-SB-(13-15) 4/29/2022 1500 13 - 15 x

AOI01-01-SB-(38-40) 4/29/2022 1550 38 - 40 x

AOI01-01-SB-(40-41) 4/29/2022 1600 40 - 41 x

AOI01-02-SB-(0-2) 4/29/2022 1110 0 - 2 x x x

AOI01-02-SB-(13-15) 4/29/2022 1335 13 - 15 x

AOI01-02-SB-(28-30) 4/29/2022 1340 28 - 30 x

AOI01-02-SB-(28-30)-MS 4/29/2022 1340 28 - 30 x MS/MSD

AOI01-02-SB-(28-30)-MSD 4/29/2022 1340 28 - 30 x MS/MSD

AOI01-03-SB-(0-2) 4/26/2022 1135 0 - 2 x

AOI01-03-SB-(9-11) 5/02/2022 0930 9 - 11 x

AOI01-03-SB-(9-11)-MS 5/02/2022 0930 9 - 11 x MS/MSD

AOI01-03-SB-(9-11)-MSD 5/02/2022 0930 9 - 11 x MS/MSD

AOI01-04-SB-(0-2) 4/26/2022 1215 0 - 2 x

AOI01-04-SB-(4-5) 5/02/2022 1025 4 - 5 x

AOI01-04-SB-(4-5)-D 5/02/2022 1025 4 - 5 x Duplicate

AOI01-05-SB-(0-2) 4/26/2022 1130 0 - 2 x

AOI01-06-SB-(0-2) 4/26/2022 1155 0 - 2 x

AOI01-07-SB-(0-2) 4/26/2022 1205 0 - 2 x

AOI01-08-SB-(0-2) 4/26/2022 1455 0 - 2 x

AOI01-09-SB-(0-2) 4/26/2022 1445 0 - 2 x

AOI01-10-SB-(0-2) 4/26/2022 1440 0 - 2 x

AOI01-11-SB-(0-2) 4/26/2022 1430 0 - 2 x

AOI01-12-SB-(0-2) 4/26/2022 1405 0 - 2

AOI01-13-SB-(0-2) 4/26/2022 1357 0 - 2 x

AOI01-14-SB-(0-2) 4/26/2022 1100 0 - 2 x

AOI01-15-SB-(0-2) 4/26/2022 1110 0 - 2 x

AOI01-16-SB-(0-2) 4/26/2022 1120 0 - 2 x

AOI01-17-SB-(0-2) 5/02/2022 1100 0 - 2 x

AOI01-18-SB-(0-2) 5/04/2022 1345 0 - 2 x

AOI01-18-SB-(13-15) 5/04/2022 1505 13 - 15 x

AOI01-19-SB-(0-2) 5/04/2022 1525 0 - 2 x

AOI01-19-SB-(10-11) 5/04/2022 1620 10 - 11 x

AOI02-01-SB-(0-2) 4/25/2022 1410 0 - 2 x

AOI02-01-SB-(12.5-15) 4/27/2022 1330 12.5 - 15 x x x

AOI02-01-SB-(25-27.5) 4/27/2022 1335 25 - 27.5 x

AOI02-01-SB-(25-27.5)-D 4/27/2022 1335 25 - 27.5 x Duplicate

AOI02-01-SB-(30-32.5) 4/27/2022 1336 30 - 32.5 x

AOI02-02-SB-(0-2) 4/25/2022 1430 0 - 2 x

AOI02-03-SB-(0-2) 4/25/2022 1435 0 - 2 x

AOI02-04-SB-(0-2) 4/25/2022 1450 0 - 2 x

Soil Samples

AECOM 5-7
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, Camp Guernsey, Guernsey, Wyoming

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) Comments

AOI03-01-SB-(0-2) 4/25/2022 1240 0 - 2 x

AOI03-01-SB-(0-2)-D 4/25/2022 1240 0 - 2 x Duplicate

AOI03-01-SB-(13-15) 4/29/2022 0916 13 - 15 x

AOI03-02-SB-(0-2) 4/25/2022 1315 0 - 2 x x x

AOI03-02-SB-(10-12.5) 4/27/2022 1655 10 - 12.5 x

AOI03-02-SB-(10-12.5)-MS 4/27/2022 1655 10 - 12.5 x MS/MSD

AOI03-02-SB-(10-12.5)-MSD 4/27/2022 1655 10 - 12.5 x MS/MSD

AOI03-03-SB-(0-2) 4/28/2022 1050 0 - 2 x

AOI03-03-SB-(13-15) 4/28/2022 1205 13 - 15 x

AOI03-03-SB-(25-27) 4/28/2022 1215 25 - 27 x

AOI03-04-SB-(0-2) 4/25/2022 1330 0 - 2 x

AOI03-04-SB-(0-2)-D 4/25/2022 1330 0 - 2 x Duplicate

AOI03-04-SB-(15-20) 4/28/2022 0940 15 - 20 x

AOI03-04-SB-(25-30) 4/28/2022 0945 25 - 30 x

AOI03-05-SB-(0-2) 4/25/2022 1330 0 - 2 x

AOI04-01-SB-(0-2) 4/25/2022 1215 0 - 2 x

AOI04-01-SB-(10-15) 4/27/2022 0930 10 - 15 x x x

AOI04-01-SB-(10-15)-D 4/27/2022 0930 10 - 15 x x Duplicate

AOI04-01-SB-(10-15)-MS 4/27/2022 0930 10 - 15 x x MS/MSD

AOI04-01-SB-(10-15)-MSD 4/27/2022 0930 10 - 15 x x MS/MSD

AOI04-01-SB-(15-20) 4/27/2022 0935 15 - 20 x

AOI04-01-SB-(15-20)-D 4/27/2022 0935 15 - 20 x Duplicate

AOI04-02-SB-(0-2) 4/25/2022 1200 0 - 2 x

AOI04-02-SB-(0-2)-MS 4/25/2022 1200 0 - 2 x MS/MSD

AOI04-02-SB-(0-2)-MSD 4/25/2022 1200 0 - 2 x MS/MSD

AOI04-03-SB-(0-2) 4/25/2022 1231 0 - 2 x

CG-01-SB-(0-2) 4/25/2022 1643 0 - 2 x

CG-01-SB-(13-15) 4/28/2022 1545 13 - 15 x

CG-01-SB-(38-40) 4/28/2022 1550 38 - 40 x

AECOM 5-8
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, Camp Guernsey, Guernsey, Wyoming

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) Comments

AOI02-01-GW 5/05/2022 1255 NA x

AOI02-01-GW-D 5/05/2022 1255 NA x Duplicate

AOI03-01-GW 5/06/2022 0820 NA x

AOI03-02-GW 5/05/2022 1520 NA x

AOI03-03-GW 5/05/2022 0940 NA x

AOI03-04-GW 5/05/2022 1410 NA x

AOI04-01-GW 5/05/2022 1210 NA x

AOI04-01-GW-D 5/05/2022 1210 NA x Duplicate

CG-01-GW 5/06/2022 0855 NA x

CG-01-GW-MS 5/06/2022 0855 NA x MS/MSD

CG-01-GW-MSD 5/06/2022 0855 NA x MS/MSD

CG-DECON-03092022 3/09/2022 1045 NA x Decon Source

CG-ERB-01 4/26/2022 1145 NA x Hand Auger

CG-ERB-02 4/27/2022 1400 NA x Drilling Equipment

CG-ERB-03 4/28/2022 0900 NA x Drilling Equipment

CG-ERB-04 4/28/2022 1055 NA x Hand Auger

CG-ERB-05 5/05/2022 1215 NA x Bladder Pump

CG-ERB-06 5/05/2022 1515 NA x Bladder Pump

CG-PW-1 5/02/2022 0940 NA x Decon Source 

CG-FRB-01 5/02/2022 0900 NA x Reagent Blank

Notes:

ASTM = American Society for Testing and Materials

bgs = below ground surface

ERB = equipment rinsate blank

FRB = field reagent blank

LC/MS/MS = Liquid Chromatography Mass Spectrometry

MS/MSD = matrix spike/ matrix spike duplicate

QSM = Quality Systems Manual

TOC = total organic carbon

USEPA = United States Environmental Protection Agency

Quality Control Samples

Groundwater Samples

AECOM 5-9
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 5-10

THIS PAGE INTENTIONALLY BLANK
Table 5-2

Soil Boring Depths and Permanent Groundwater Sample Point Screen Intervals

Site Inspection Report, Camp Guersney, Wyoming

Area of 

Interest

Boring 

Location

Groundwater 

Sampling Point ID

Soil Boring 

Depth 

(feet bgs)

Groundwater Sampling 

Point Screen Interval 

(feet bgs)

1 CG-01 CG-01 50 40-50

2 AOI02-01 AOI02-01 35 25-35

AOI03-01 AOI03-01 35 25-35

AOI03-02 AOI03-02 32.5 20-30

AOI03-03 AOI03-03 35 23-33

AOI03-04 AOI03-04 40 25-35

4 AOI04-01 AOI04-01 25 15-25

Notes:

AOI = Area of Interest

bgs = below ground surface

CG = Camp Guernsey

ID = identification

3

AECOM 5-11
Table 5-3

Permanent Groundwater Sample Point Screen Intervals, and Groundwater Elevations

Site Inspection Report, Camp Guernsey, Guernsey, Wyoming

Area of 

Interest

Boring 

Location

Soil Boring 

Depth 

(feet bgs)

Groundwater 

Sampling Point 

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)

AOI01-01 41 - - 4352.47 - - -

AOI01-02 30 - - 4348.83 - - -

AOI01-03 11 - - 4391.88 - - -

AOI01-04 5.5 - - 4372.24 - - -

AOI01-18 16 - - 4328.07 - - -

AOI01-19 11 - - 4320.40 - - -

CG-01 50 40-50 4348.73 4349.04 40.05 40.36 4308.68

2 AOI02-01 35 25-35 4348.07 4348.37 22.43 22.73 4325.64

AOI03-01 35 25-35 4336.36 4336.57 28.17 28.38 4308.19

AOI03-02 32.5 20-30 4333.61 4333.91 25.48 25.78 4308.13

AOI03-03* 35 23-33 - - 27.08 - -

AOI03-04 40 25-35 4338.67 4339.07 29.76 30.16 4308.91

4 AOI04-01 25 15-25 4325.59 4326.35 18.96 19.72 4306.63

Notes:

* = Survey data was not collected for this location

bgs = below ground surface

btoc = below top of casing

NA = not applicable

NAVD88 = North American Vertical Datum 1988

3

1

AECOM 5-12
!?

!?

!?

!?

!?

!? !? !?

!?

!?

!?

"S

"S

"S

"S

"S

"S

"S

"S

"S

"S

"S

"S

"S

"S

"S

"S

"S

"S !?

!?

"S

North Platte River

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI02-01

AOI03-01

AOI03-03 AOI03-02

AOI03-04

AOI04-01

CG-01

AOI01-07

AOI01-06

AOI01-05 AOI01-08

AOI01-09

AOI01-10

AOI01-16

AOI01-11

AOI01-12

AOI01-15

AOI03-05

AOI04-02

AOI04-03

AOI01-14

AOI01-13

AOI02-04

AOI02-03

AOI02-02

AOI01-18

AOI01-19

AOI01-17

AOI 1

AOI 2

AOI 3

AOI 4

­12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

AG

3/6/2023

3/6/2023

PROJECT Site Inspection at Camp Guernsey, WY

3/6/2023

1:10,200

PM CM 3/6/2023 Base Map: Sources: Esri, HERE, Garmin, USGS,

Intermap, INCREMENT P, NRCan, Esri Japan, METI,

Figure 5-1

Site Inspection Sample Locations

Legend

!? Soil Boring/Groundwater Sampling Point

!? Soil Boring

"S Surface Soil Sample

Area of Interest

Facility Boundary

Water Body

Surface Water Flow Direction

Groundwater Flow Direction

0 425 850 1,700

Feet

AECOM 5-13
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 5-14

THIS PAGE INTENTIONALLY BLANK
Site Inspection Report

Camp Guernsey, Wyoming

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

Camp Guernsey, Wyoming

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 sampling.

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

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

Council (ITRC), several important 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 in comparison to SLs for AOI 1: Camp 

Guernsey Airfield. The soil results are summarized on Table 6-2 through Table 6-4. Soil results 

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

6.3.1 AOI 1 Soil Analytical Results

Surface soil was sampled from 0 to 2 feet bgs at boring locations AOI01-01 through AOI01-19

and CG-01. Soil was also sampled from shallow subsurface soil (4 to 15 feet bgs) at boring 

locations AOI01-1 through AOI01-03, AOI01-18, AOI01-19, and CG-01, and deep subsurface soil

intervals (25 to 40 feet bgs) at boring locations AOI01-01, AOI01-02, and CG-01. 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.

PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in surface soil at concentrations below 

the residential SLs. Detections were observed at sample locations surrounding the AOI and were 

generally highest near the paved areas and in the direction of expected surface water flow. The 

maximum detected concentration of these compounds in surface soil was PFHxS, at 13.7 

micrograms per kilogram (μg/kg) at AOI01-06.

In shallow subsurface soil, PFOS and PFHxS were detected below the industrial/commercial SLs. 

The maximum detected concentration of these compounds was PFHxS, at 0.794 J μg/kg at 

AOI01-01 (13 to 15 feet bgs). PFOA, PFBS, and PFNA were not detected in shallow subsurface 

soil.

In deep subsurface soil PFBS and PFHxS were detected. The maximum detected concentration 

was PFHxS, at 0.138 J μg/kg at AOI01-01 (38 to 40 feet bgs). PFOA, PFOS, and PFNA were not 

detected in deep subsurface soil. There are no SLs for deep subsurface soil.

6.3.2 AOI 1 Groundwater Analytical Results

Groundwater was sampled from permanent groundwater sampling point CG-01, located outside

the boundary of AOI 1, but near the base of the terrace on which AOI 1 is situated. CG-01 is 

located at the bottom of Bridger Avenue before it climbs up to Fire House #1 and the north end of 

the AOI. This location was identified to evaluate groundwater upgradient from the source areas 

based on the understanding of the CSM during SI planning. SI findings suggest conditions in 
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 6-3

groundwater at CG-01 may reflect potential unknown upgradient sources on- or off-facility, or the 

northern part of the airfield. Figure 6-6 and Figure 6-7 present the ranges of detections in 

groundwater. Table 6-5 summarizes the groundwater results. 

The following exceedances were detected in groundwater at CG-01:

• PFOA was detected above the 6 ng/L SL, at a concentration of 79.2 ng/L.

• PFHxS was detected above the 39 ng/L SL, at a concentration of 438 J ng/L. 

PFOS and PFBS were detected below the SLs at AOI 1, at concentrations of 1.13 J ng/L and 128 

ng/L. PFNA was not detected.

6.3.3 AOI 1 Conclusions

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

below the SLs. PFOA and PFHxS were detected in groundwater, above the SLs. Based on the 

exceedances of the SLs in groundwater, further evaluation at AOI 1 is warranted.

6.4 AOI 2

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

AOI 2: Current Firetruck Maintenance Areas. The results in soil and groundwater are summarized 

on Table 6-2 through Table 6-5. Soil and groundwater results are presented on Figure 6-1

through Figure 6-7.

6.4.1 AOI 2 Soil Analytical Results

Surface soil was sampled from 0 to 2 feet bgs at boring locations AOI02-01 through AOI02-04. 

Soil was also sampled from shallow subsurface soil (12.5 to 15 feet bgs) and deep subsurface 

soil intervals (25 to 27.5 feet bgs) at boring location AOI02-01. 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.

PFOA, PFOS, PFHxS, and PFNA were detected in surface soil below the residential SLs. The 

maximum detected concentration of these compounds was PFOS at 0.896 J μg/kg at AOI02-02. 

PFBS was not detected in surface soil.

PFOA, PFOS, PFBS, PFHxS, and PFNA were not detected in shallow or deep subsurface soil.

6.4.2 AOI 2 Groundwater Analytical Results

Groundwater was sampled from permanent groundwater sampling point AOI2-01. Figure 6-6 and 

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

groundwater results.

PFOA, PFOS, PFBS, and PFHxS were detected in groundwater below their SLs. PFNA was not 

detected at AOI 2. A summary of results is provided below:

• PFOA was detected below the 6 ng/L SL, at a concentration of 0.726 J ng/L. 

• PFOS was detected below the 4 ng/L SL, at a concentration of 0.517 J ng/L.

• PFBS was detected below the 601 ng/L SL, at a concentration of 18.9 ng/L.

• PFHxS was detected below the 39 ng/L SL, at a concentration of 8.55 ng/L. 
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 6-4

6.4.3 AOI 2 Conclusions

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

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

at concentrations below their SLs. Therefore, further evaluation at AOI 2 is not warranted at this 

time.

6.5 AOI 3

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

AOI 3: Historic Maintenance and Storage Areas. The results in soil and groundwater are 

presented in Table 6-2 through Table 6-5. Soil and groundwater results are presented on Figure 

6-1 through Figure 6-7.

6.5.1 AOI 3 Soil Analytical Results

Surface soil was sampled from 0 to 2 feet bgs at boring locations AOI03-01 through AOI03-05. 

Soil was also sampled from shallow subsurface soil (10 to 15 feet bgs) at boring locations AOI03-

1 through AOI03-03, and deep subsurface soil intervals (15 to 40 feet bgs) at boring locations 

AOI03-03 and AOI03-04. 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.

PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in surface soil below the residential SLs. 

The maximum detected concentration of these compounds was PFOS at 2.14 μg/kg at AOI03-

02. 

PFOA, PFOS, PFBS, PFHxS, and PFNA were not detected in shallow subsurface soil. In deep 

subsurface soil, PFOA, PFOS, PFHxS, and PFNA were detected. The maximum detected 

concentration was PFOS at 1.90 μg/kg at AOI03-04 (25 to 30 feet bgs). PFBS was not detected 

in deep subsurface soil.

6.5.2 AOI 3 Groundwater Analytical Results

Groundwater was sampled from permanent groundwater sampling points AOI03-01 through 

AOI03-04. Figure 6-6 and Figure 6-7 present the ranges of detections in groundwater. Table 6-

5 summarizes the groundwater results.

PFOA, PFOS, PFBS, and PFHxS were detected in groundwater below their SLs. PFNA was not 

detected at AOI 3. A summary of detected results is provided below:

• PFOA was detected below the 6 ng/L SL, at a maximum concentration of 0.606 J ng/L

at AOI03-04. 

• PFOS was detected below the 4 ng/L SL, at a maximum concentration of 1.34 J ng/L at 

AOI03-03. 

• PFBS was detected below the 601 ng/L, SL at a maximum concentration of 11.9 ng/L

at AOI03-01.

• PFHxS was detected below the 39 ng/L, SL at a maximum concentration of 5.24 ng/L

at AOI03-01. 

6.5.3 AOI 3 Conclusions

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

concentrations below their SLs. PFOA, PFOS, PFBS, and PFHxS were detected in groundwater,
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 6-5

at concentrations below their SLs. Therefore, further evaluation at AOI 3 is not warranted at this 

time.

6.6 AOI 4

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

4: Outdoor Wash Rack. The results in soil and groundwater are presented in Table 6-2 through 

Table 6-5. Soil and groundwater results are presented on Figure 6-1 through Figure 6-7.

6.6.1 AOI 4 Soil Analytical Results

Surface soil was sampled from 0 to 2 feet bgs at boring locations AOI04-01 through AOI04-03. 

Soil was also sampled from shallow subsurface soil (10 to 15 feet bgs) and deep subsurface soil 

intervals (15 to 20 feet bgs) at boring location AOI04-01. 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.

PFOA, PFOS, and PFHxS were detected in surface soil below the residential SLs. The maximum 

detected concentration of these compounds was PFOS, at 0.933 J μg/kg at AOI04-01. PFBS and 

PFNA were not detected in surface soil.

PFOA, PFOS, PFBS, PFHxS, and PFNA were not detected in shallow subsurface soil. In deep 

subsurface soil, only PFBS and PFHxS were detected, with a maximum detected concentration

of 0.123 J μg/kg for PFHxS at AOI04-01 (15 to 20 feet bgs).

6.6.2 AOI 4 Groundwater Analytical Results

Groundwater was sampled from permanent groundwater sampling point AOI04-01. This location 

was identified to evaluate AOI 4 based on the inferred groundwater flow direction during SI 

planning. SI findings suggest AOI04-01 may be downgradient of several potential release areas, 

including the wash rack. Therefore, groundwater results at AOI04-01 may reflect one or more 

source areas but are used here for evaluation of AOI 4 only. This data gap will be addressed 

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

6-5 summarizes the groundwater results. 

The following exceedance of the SLs was measured at AOI04-01: 

• PFOS was detected above the 4 ng/L, at a concentration of 4.21 ng/L.

PFOA, PFBS, and PFHxS were detected at concentrations below their SLs. PFNA was not 

detected at AOI 4.

6.6.3 AOI 4 Conclusions

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

PFOS was detected in groundwater at a concentration above the SL. Based on the exceedance 

of the PFOS SL in groundwater, further evaluation at AOI 4 is warranted.
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 6-6

THIS PAGE INTENTIONALLY BLANK
Table 6-2

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

Site Inspection Report, Camp Guernsey

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Resu

PFBS 1900 ND U ND U ND U ND U ND U ND U 0.021 J ND U ND PFHxS 130 0.035 J 0.034 J 0.044 J 0.175 J 0.146 J 0.123 J 13.7 0.595 J 0.120 

PFNA 19 0.048 J 0.043 J ND U ND U ND U ND U ND U 0.054 J 0.043 PFOA 19 ND U ND U ND U 0.140 J 0.177 J 0.170 J 3.00 0.454 J ND 

PFOS 13 3.03 2.68 0.096 J 0.466 J 0.235 J 0.205 J 4.00 1.30 1.17 

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 CG Camp Guernsey

UJ = The analyte was not detected at a level greater than or equal to the adjusted DL. However, the reported adjusted DL is approximate and may be inaccurate or imprecise. 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 tandem mLOD limit of detectionND analyte not detected above the LODOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierSB soil boringUSEPA United States Environmental Protectioμg/kg micrograms per kilogram

AOI01-06-SB-(0-2)

04/26/2022

0-2 ft

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

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

AOI01-07-SB-(0-2)

04/26/2022

0-2 ft

AOI0

04

AOI01-05-SB-(0-2)

0-2 ft

AOI01-04-SB-(0-2)

04/26/2022

0-2 ft

04/26/2022

0-2 ft

Area of Interest

Sample ID

Sample Date

Depth

AOI01-01-SB-(0-2)

04/29/2022

0-2 ft

AOI01

AOI01-01-SB-(0-2)-D

04/29/2022

0-2 ft

AOI01-02-SB-(0-2)

04/29/2022

0-2 ft

AOI01-03-SB-(0-2)

04/26/2022

AECOM 
Table 6-2

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

Site Inspection Report, Camp Guernsey

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Resu

PFBS 1900 ND U ND U ND U 0.044 J ND U ND U ND U ND U ND PFHxS 130 0.121 J 0.046 J 4.64 4.37 0.239 J 0.066 J 0.273 J ND U 0.166 PFNA 19 ND U ND U 0.507 J 0.096 J 0.027 J 0.052 J 0.028 J ND U ND PFOA 19 0.088 J ND U 0.707 J 0.856 J 0.270 J 0.128 J 0.293 J ND U 0.140 PFOS 13 0.459 J 0.166 J 5.09 1.78 0.965 J 1.11 2.30 0.548 J 0.096 

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 CG Camp Guernsey

UJ = The analyte was not detected at a level greater than or equal to the adjusted DL. However, the reported adjusted DL is approximate and may be inaccurate or imprecise. 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 tandem mLOD limit of detectionND analyte not detected above the LODOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierSB soil boringUSEPA United States Environmental Protectioμg/kg micrograms per kilogram

AOI01-16-SB-(0-2)

04/26/2022

0-2 ft

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

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

AOI01-17-SB-(0-2)

05/02/2022

0-2 ft

AOI0

0

AOI01-15-SB-(0-2)

0-2 ft

AOI01-14-SB-(0-2)

04/26/2022

0-2 ft

04/26/2022

0-2 ft

Area of Interest

Sample ID

Sample Date

Depth

AOI01-10-SB-(0-2)

04/26/2022

0-2 ft

AOI01

AOI01-11-SB-(0-2)

04/26/2022

0-2 ft

AOI01-12-SB-(0-2)

04/26/2022

0-2 ft

AOI01-13-SB-(0-2)

04/26/2022

AECOM 
Table 6-2

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

Site Inspection Report, Camp Guernsey

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Resu

PFBS 1900 ND U ND U ND U ND U ND U ND U ND U ND U ND PFHxS 130 0.079 J 0.167 J 0.158 J ND U 0.046 J 0.114 J 0.105 J 0.094 J 0.034 PFNA 19 0.025 J 0.023 J 0.043 J 0.038 J ND U 0.051 J 0.050 J 0.130 J ND PFOA 19 ND U 0.122 J 0.144 J ND U ND U 0.087 J ND UJ 0.149 J ND PFOS 13 0.484 J 0.270 J 0.896 J 0.231 J 0.267 J 0.806 J 0.790 J 2.14 0.113 

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluoro

References PFHxS perfluoro

PFNA perfluoroPFOA perfluoroPFOS perfluoro

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AOI Area of IU = The analyte was not detected at a level greater than or equal to the adjusted DL CG Camp G

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

DL detection 

Notes ft feet

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

ID identificaLCMSMS liquid chrLOD limit of dND analyte nOSD Office of QSM Quality SQual interpreteSB soil borinUSEPA United Sμg/kg microgra

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.

AOI0

04

AOI03-01-SB-(0-2)-D

0-2 ft

AOI03-01-SB-(0-2)

04/25/2022

0-2 ft

AOI02-03-SB-(0-2)

04/25/2022

0-2 ft

AOI02-04-SB-(0-2)

0-2 ft

AOI03

04/25/2022

0-2 ft

AOI03-02-SB-(0-2)

04/25/2022

0-2 ft

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

Area of Interest

Sample ID

Sample Date

Depth

AOI02-01-SB-(0-2)

04/25/2022

0-2 ft

AOI02

AOI02-02-SB-(0-2)

04/25/2022

0-2 ft

04/25/2022

AOI01

CG-01-SB-(0-2)

04/25/2022

AECOM 
Table 6-2

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

Site Inspection Report, Camp Guernsey

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual

PFBS 1900 0.025 J ND U ND U ND U ND UPFHxS 130 0.107 J 0.036 J 0.724 J 0.079 J 0.147 JPFNA 19 0.038 J 0.154 J ND U ND U ND UPFOA 19 0.136 J 0.254 J 0.449 J ND U 0.224 JPFOS 13 0.595 J 1.08 0.933 J 0.157 J 0.772 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 CG Camp Guernsey

UJ = The analyte was not detected at a level greater than or equal to the adjusted DL. However, the reported adjusted DL is approximate and may be inaccurate or imprecise. 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 tandem mLOD limit of detectionND analyte not detected above the LODOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierSB soil boringUSEPA United States Environmental Protectioμg/kg micrograms per kilogram

AOI04

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.

AOI04-03-SB-(0-2)

04/25/2022

0-2 ft

04/25/2022

0-2 ft

AOI04-01-SB-(0-2)

04/25/2022

0-2 ft

AOI04-02-SB-(0-2)

Area of Interest

Sample ID

Sample Date

Depth

AOI03-05-SB-(0-2)

04/25/2022

0-2 ft

AOI03-04-SB-(0-2)-D

04/25/2022

0-2 ft

AOI03

AECOM 
Table 6-3

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

Site Inspection Report, Camp Guernsey

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Re

PFBS 25000 ND U ND U ND U ND U ND U ND U ND U ND U ND PFHxS 1600 0.794 J ND U ND U ND UJ 0.041 J ND U 0.099 J ND U ND PFNA 250 ND U ND U ND U ND U ND U ND U ND U ND U ND PFOA 250 ND U ND U ND U ND U ND U ND U ND U ND U ND PFOS 160 ND U ND U ND U 0.053 J 0.077 J ND U 0.072 J 0.110 J ND 

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 CG Camp GuernseyUJ = The analyte was not detected at a level greater than or equal to the adjusted DL. However, the reported adjusted DL is approximate and may be inaccurate or imprecise. 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 tandem LOD limit of detectionND analyte not detected above the LODOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierSB soil boringUSEPA United States Environmental Protecμg/kg micrograms per kilogram

Area of Interest

Sample ID

Sample Date

Depth

AOI01-01-SB-(13-15)

04/29/2022

13-15 ft

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

AOI01-18-SB-(13-15)

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

5/4/2022

13-15 ft

AOI01-19-SB-(10-11)

5/4/2022

10-11 ft

05/02/2022

4-5 ft

AOI01-04-SB-(4-5)-D

05/02/2022

CG-01-SB-(13-15)

04/28/2022

13-15 ft

AOI01 

AOI0

4-5 ft 

AOI01-02-SB-(13-15)

04/29/2022

13-15 ft

AOI01-03-SB-(9-11)

05/02/2022

9-11 ft

AOI01-04-SB-(4-5)

AECOM 
Table 6-3

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

Site Inspection Report, Camp Guernsey

Analyte OSD Screening 

Level a

Result Qual Result Qual

Soil, LCMSMS compliantE537M

PFBS 25000 ND UJ ND U ND UPFHxS 1600 ND UJ ND U ND UPFNA 250 ND UJ ND U ND UPFOA 250 ND UJ ND U ND UPFOS 160 ND UJ ND U ND U

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluo

References PFHxS perfluo

PFNA perfluoPFOA perfluoPFOS perfluo

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AOI Area oU = The analyte was not detected at a level greater than or equal to the adjusted DL CG Camp 

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

DL detecti

Notes ft feet

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

ID identificLCMSMS liquid cLOD limit of ND analyte OSD Office oQSM Quality Qual interpreSB soil boUSEPA United μg/kg microg

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.

AOI04

AOI04-01-SB-(10-15)

04/27/2022

10-15 ft

Area of Interest

Sample ID

Sample Date

Depth 10-12.5 ft

AOI03

AOI03-02-SB-(10-12.5) AOI03-03-SB-(13-15)

04/27/2022 04/28/2022

13-15 ft

AECOM 
Table 6-4

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

Site Inspection Report, Camp Guernsey

Area of Interest

Sample ID

Sample Date

Depth

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

PFBS 0.034 J ND U ND U ND U ND U ND U ND U ND UPFHxS 0.138 J ND U ND U ND U ND U ND U ND U 0.228 JPFNA ND U ND U ND U ND U ND U ND U ND U 0.028 JPFOA ND U ND U ND U ND U ND U ND U ND U 0.078 JPFOS ND U ND U ND U ND U ND U ND U ND U 1.90

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

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

PFOA perfluorooctanoic acid

Notes PFOS perfluorooctanesulfonic acid

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

Acronyms and AbbreviationsAOI Area of InterestCG Camp GuernseyD duplicateDL detection limitft feetID identificationLCMSMS liquid chromatography with tandem LOD limit of detectionND analyte not detected above the LODQSM Quality Systems ManualQual interpreted qualifierSB soil boringμg/kg micrograms per kilogram

AOI01

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

AOI03-03-SB-(25-27)

04/28/2022

25-27 ft

AOI03-04-SB-(15-20)

04/28/2022

15-20 ft

AOI02-01-SB-(25-27.5)

04/27/2022

AOI03

AOI01-01-SB-(38-40)

04/29/2022

38-40 ft

AOI01-02-SB-(28-30)

04/29/2022

28-30 ft 25-27.5 ft

CG-01-SB-(38-40)

04/28/2022

38-40 ft

AOI02-01-SB-(25-27.5)-D

04/27/2022

25-27.5 ft

AOI02

AOI03-04-SB-(25-30)

04/28/2022

25-30 ft

AECOM 
Table 6-4

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

Site Inspection Report, Camp Guernsey

Area of Interest

Sample ID

Sample Date

Depth

Analyte Result Qual Result Qual

Soil, LCMSMS compliantE537M

PFBS 0.020 J ND UJPFHxS 0.123 J 0.106 JPFNA ND U ND UPFOA ND U ND UPFOS ND U ND U

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

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

PFOA perfluorooctanoic acid

Notes PFOS perfluorooctanesulfonic acid

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

Acronyms and AbbreviationsAOI Area of InterestCG Camp GuernseyD duplicateDL detection limitft feetID identificationLCMSMS liquid chromatography with tandem maLOD limit of detectionND analyte not detected above the LODQSM Quality Systems ManualQual interpreted qualifierSB soil boringμg/kg micrograms per kilogram

AOI04

AOI04-01-SB-(15-20)

04/27/2022

15-20 ft

AOI04-01-SB-(15-20)-D

04/27/2022

15-20 ft

AECOM 
Table 6-5

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

Site Inspection Report, Camp Guernsey

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Res

PFBS 601 128 18.9 16.5 11.9 ND U 0.969 J 1.46 J 4.24 3.95

PFHxS 39 438 J 8.55 7.78 5.24 ND U 2.49 1.15 J 28.5 25.4

PFNA 6 ND U ND U ND U ND U ND U ND U ND U ND U ND PFOA 6 79.2 0.726 J 0.666 J ND U ND U ND U 0.606 J 1.86 J 1.65 PFOS 4 1.13 J 0.517 J 0.421 J 0.618 J ND U 1.34 J 1.06 J 4.21 3.77

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluo

References PFHxS perfluo

PFNA perfluoPFOA perfluoPFOS perfluo

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AOI Area oU = The analyte was not detected at a level greater than or equal to the adjusted DL CG Camp 

D duplica

Notes DL detecti

ND = Analyte not detected above the LOD. LOD values are presented in Appendix F. GW ground

HQ hazard ID identificLCMSMS liquid cLOD limit of ND analyte OSD Office oQSM Quality Qual interpreUSEPA United ng/l nanogr

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.

AO

AOI01

CG-01-GW

05/06/2022

AOI03-04-GW

05/05/2022

AOI04-01-GW

05/05/2022

AOI03-02-GW

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

Area of Interest AOI04

Sample ID

Sample Date

AOI02-01-GW

05/05/2022

AOI02

05/05/2022

AOI03-03-GW

05/05/2022

AOI02-01-GW-D

05/05/2022

AOI03-01-GW

05/06/2022

AOI03

AECOM 
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 6-16

THIS PAGE INTENTIONALLY BLANK
AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI02-01

AOI03-01

AOI03-02

AOI03-03

AOI03-04

AOI04-01

CG-01

AOI01-07

AOI01-06

AOI01-05 AOI01-08

AOI01-09

AOI01-10

AOI01-16

AOI01-11

AOI01-12

AOI01-15

AOI03-05

AOI04-02

AOI04-03

AOI01-14

AOI01-13

AOI02-04

AOI02-03

AOI02-02

AOI01-18

AOI01-19

AOI01-17

Legend

Facility Boundary

Water Body

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI02-01

AOI03-01

AOI03-02

AOI03-03

AOI03-04

AOI04-01

CG-01

AOI01-18

AOI01-19

AOI01-01

AOI01-02

AOI02-01

AOI03-03

AOI03-04

AOI04-01

CG-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-1

PFOA Detections in Soil

3/3/2023

3/3/2023

MS 3/3/2023

AG

CM

GIS BY

CHK BY

PM

3/3/2023

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Camp Guernsey, WY

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

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

1:8,880

Shallow

Intermediate

Deep

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

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

PFOA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

0 370

­

740 1,480

Feet

AECOM 6-17
AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI02-01

AOI03-01

AOI03-02

AOI03-03

AOI03-04

AOI04-01

CG-01

AOI01-07

AOI01-06

AOI01-05 AOI01-08

AOI01-09

AOI01-10

AOI01-16

AOI01-11

AOI01-12

AOI01-15

AOI03-05

AOI04-02

AOI04-03

AOI01-14

AOI01-13

AOI02-04

AOI02-03

AOI02-02

AOI01-18

AOI01-19

AOI01-17

Legend

Facility Boundary

Water Body

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI02-01

AOI03-01

AOI03-02

AOI03-03

AOI03-04

AOI04-01

CG-01

AOI01-18

AOI01-19

AOI01-01

AOI01-02

AOI02-01

AOI03-03

AOI03-04

AOI04-01

CG-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-2

PFOS Detections in Soil

3/3/2023

3/3/2023

MS 3/3/2023

AG

CM

GIS BY

CHK BY

PM

3/3/2023

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Camp Guernsey, WY

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

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

1:8,880

Shallow

Intermediate

Deep

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

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

0 370

­

740 1,480

Feet

PFOS Results (μg/Kg)

ND

>ND - 13

>13 - 160

>160 - 1,600

>1,600

AECOM 6-18
AOI01-01 AOI01-02

AOI01-03

AOI01-04

AOI02-01

AOI03-01

AOI03-02

AOI03-03

AOI03-04

AOI04-01

CG-01

AOI01-07

AOI01-06

AOI01-05 AOI01-08

AOI01-09

AOI01-10

AOI01-16

AOI01-11

AOI01-12

AOI01-15

AOI03-05

AOI04-02

AOI04-03

AOI01-14

AOI01-13

AOI02-04

AOI02-03

AOI02-02 AOI01-18

AOI01-19

AOI01-17

Legend

Facility Boundary

Water Body

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI02-01

AOI03-01

AOI03-02

AOI03-03

AOI03-04

AOI04-01

CG-01

AOI01-18

AOI01-19

AOI01-01

AOI01-02

AOI02-01

AOI03-03

AOI03-04

AOI04-01

CG-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-3

PFBS Detections in Soil

3/3/2023

3/3/2023

MS 3/3/2023

AG

CM

GIS BY

CHK BY

PM

3/3/2023

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Camp Guernsey, WY

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

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

1:8,880

Shallow

Intermediate

Deep

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

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

0 370

­

740 1,480

Feet

PFBS Results (μg/Kg)

ND

>ND - 10

>10 - 1,900

>1,900 - 25,000

>25,000

AECOM 6-19
AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI02-01

AOI03-01

AOI03-02

AOI03-03

AOI03-04

AOI04-01

CG-01

AOI01-07

AOI01-06

AOI01-05 AOI01-08

AOI01-09

AOI01-10

AOI01-16

AOI01-11

AOI01-12

AOI01-15

AOI03-05

AOI04-02

AOI04-03

AOI01-14

AOI01-13

AOI02-04

AOI02-03

AOI02-02

AOI01-18

AOI01-19

AOI01-17

Legend

Facility Boundary

Water Body

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI02-01

AOI03-01

AOI03-02

AOI03-03

AOI03-04

AOI04-01

CG-01

AOI01-18

AOI01-19

AOI01-01

AOI01-02

AOI02-01

AOI03-03

AOI03-04

AOI04-01

CG-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-4

PFHxS Detections in Soil

3/3/2023

3/3/2023

MS 3/3/2023

AG

CM

GIS BY

CHK BY

PM

3/3/2023

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Camp Guernsey, WY

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

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

1:8,880

Shallow

Intermediate

Deep

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

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

0 370

­

740 1,480

Feet

PFHxS Results (μg/Kg)

ND

>ND - 10

>10 - 130

>130 - 1,600

>1,600

AECOM 6-20
AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI02-01

AOI03-01

AOI03-02

AOI03-03

AOI03-04

AOI04-01

CG-01

AOI01-07

AOI01-06

AOI01-05 AOI01-08

AOI01-09

AOI01-10

AOI01-16

AOI01-11

AOI01-12

AOI01-15

AOI03-05

AOI04-02

AOI04-03

AOI01-14

AOI01-13

AOI02-04

AOI02-03

AOI02-02 AOI01-18

AOI01-19

AOI01-17

Legend

Facility Boundary

Water Body

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI02-01

AOI03-01

AOI03-02

AOI03-03

AOI03-04

AOI04-01

CG-01

AOI01-18

AOI01-19

AOI01-01

AOI01-02

AOI02-01

AOI03-03

AOI03-04

AOI04-01

CG-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-5

PFNA Detections in Soil

3/3/2023

3/3/2023

MS 3/3/2023

AG

CM

GIS BY

CHK BY

PM

3/3/2023

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Camp Guernsey, WY

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

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

1:8,880

Shallow

Intermediate

Deep

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

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

0 370

­

740 1,480

Feet

PFNA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

AECOM 6-21
AOI02-01

AOI03-01

AOI03-02

AOI03-03

AOI03-04

AOI04-01

CG-01

Legend

Facility Boundary

Water Body

Groundwater Flow Direction

Inferred Groundwater Flow Direction

AOI02-01

AOI03-01

AOI03-02

AOI03-03

AOI03-04

AOI04-01

CG-01

AOI02-01

AOI03-01

AOI03-02

AOI03-03

AOI03-04

AOI04-01

CG-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-6

PFOA, PFOS, PFBS Detections

in Groundwater

3/6/2023

3/6/2023

MS 3/6/2023

AG

CM

GIS BY

CHK BY

PM

3/6/2023

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Camp Guernsey, WY

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

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

1:8,880

PFOA

PFOS

PFBS

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

0 370

­

740 1,480

Feet

AECOM 6-22
AOI02-01

AOI03-01

AOI03-02

AOI03-03

AOI03-04

AOI04-01

CG-01

Legend

Facility Boundary

Water Body

Groundwater Flow Direction

Inferred Groundwater Flow Direction

AOI02-01

AOI03-01

AOI03-02

AOI03-03

AOI03-04

AOI04-01

CG-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-7

PFHxS and PFNA Detections

in Groundwater

3/6/2023

3/6/2023

MS 3/6/2023

AG

CM

GIS BY

CHK BY

PM

3/6/2023

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Camp Guernsey, WY

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

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

1:8,880

PFHxS

PFNA

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

0 370

­

740 1,480

Feet

AECOM 6-23
Site Inspection Report Camp 

Guernsey, Wyoming 

THIS PAGE INTENTIONALLY BLANK 
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 7-1

7. Exposure Pathways

The CSMs for each AOI, revised based on the SI findings, are presented on Figure 7-1 through 

Figure 7-4. Please note that while the CSM discussion assists in determining if a receptor may 

be impacted, the decision to move from SI to RI or interim action is determined based upon 

exceedances of the SLs for the relevant compounds and whether the release is more than likely 

attributable to the DoD. A CSM presents the current understanding of the site conditions with 

respect to known and suspected sources, potential transport mechanisms and migration 

pathways, and potentially exposed human receptors. A human exposure pathway is considered 

potentially complete when the following conditions are present:

1. Contaminant source;

2. Environmental fate and transport;

3. Exposure point;

4. Exposure route; and

5. Potentially exposed populations.

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

circle symbol to represent an incomplete exposure pathway. Areas with an incomplete pathway 

generally warrant no further action. However, the pathway is considered potentially complete if the 

relevant compounds are detected, in which case the CSM figure uses a half-filled circle symbol to 

represent a potentially complete exposure pathway. Additionally, a completely filled circle symbol is 

used to indicate when a potentially complete exposure pathway has detections of relevant 

compounds above the SLs. Areas with an identified potentially complete pathway that have 

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

the CSMs indicate whether potentially complete exposure pathways may exist, the 

recommendation for future study in an RI or no action at this time is based on the comparison of 

the SI analytical results for the relevant compounds to the SLs.

In general, the potential routes of exposure to the relevant compounds are ingestion and 

inhalation. Human exposure via the dermal contact pathway may occur, and current risk practice 

suggests it is an insignificant pathway compared to ingestion; however, exposure data for dermal 

pathways are sparse and continue to be the subject of toxicological study. The receptors 

evaluated are consistent with those listed in USEPA guidance for risk screening (USEPA, 2001). 

Receptors at the facility include site workers (e.g., facility staff and visiting soldiers), construction 

workers, trespassers, residents outside the facility boundary, and recreational users outside of 

the facility boundary. 

7.1 Soil Exposure Pathway

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

between the source and potential receptors at AOI 1, AOI 2, AOI 3, and AOI 4 based on the 

aforementioned criteria. 

7.1.1 AOI 1 

AOI 1 consists of Camp Guernsey Airfield, where controlled AFFF releases through familiarization 

training have occurred every 2 years beginning as early as the 1990s until 2004. Additional fire 

training or releases of AFFF may have occurred as recently as 2013 based on WYARNG provided 

aerial imagery. Firetrucks have been stationed at Fire House #1 or at the fire station parking 

annex. Fire House #1 was constructed in 1988 and is also used for firetruck cleaning. Additionally, 
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 7-2

AFFF is stored in a warehouse next to Airfield Operations. Releases at AOI 1 may have occurred 

directly onto surface soil but may also have run off to surface soil or infiltrated to the subsurface 

soil via cracks in pavement or joints between areas that are paved with different materials. 

Relevant compounds were detected below the SLs in surface soil at AOI 1. Site workers and 

construction workers could contact these constituents in surface soil via incidental ingestion and 

inhalation of dust. No ongoing construction was observed at the facility during the SI; therefore, 

the surface soil exposure pathway for site workers and future construction workers are potentially 

complete. The incidental ingestion and inhalation of dust exposure pathways for the trespasser

receptor are considered potentially complete due to the potential for unauthorized access on 

Camp Guernsey. Residential structures are not located in the vicinity of AOI 1; therefore, the 

incidental ingestion and inhalation of dust exposure pathways for the residential receptors are 

considered incomplete. The industrial/commercial worker exposure scenario assumes excavation 

occurs at depths at or above 15 feet bgs. Relevant compounds were detected below the SLs in 

shallow subsurface soil (defined as 2 to 15 feet bgs) at AOI 1. Construction workers could contact 

constituents in shallow subsurface soil via incidental ingestion; therefore, the subsurface soil 

exposure pathway for future construction workers is potentially complete. The CSM for AOI 1 is 

presented on Figure 7-1. 

7.1.2 AOI 2 

AOI 2 comprises an area east of the runway, where firetruck maintenance is reported to occur. 

This area includes the current UTES, CSMS, and FMS #5, which were constructed in 2001. 

Firetrucks may have used the interior wash racks within the CSMS and FMS #5 buildings. It is 

unknown if AFFF were in the firetrucks during maintenance or washing, if AFFF were potentially 

released during maintenance, and if firetrucks cleaned at the wash rack had residual AFFF on the 

exterior of the trucks. Any AFFF releases would have occurred on paved/concrete areas. AFFF 

released to the pavement or concrete could have run off to surface soil or infiltrated subsurface 

soil via cracks in pavement/concrete or joints between areas that are paved with different 

materials.

Relevant compounds were detected below the SLs in surface soil at AOI 2. Site workers and

future construction workers could contact these constituents in surface soil via incidental ingestion 

and inhalation of dust. Therefore, the surface soil exposure pathway for these receptors is

potentially complete. The incidental ingestion and inhalation of dust exposure pathways for 

trespassers are considered potentially complete due to the potential for unauthorized access on 

Camp Guernsey. Residential structures are not located in the vicinity of AOI 2; therefore, the 

incidental ingestion and inhalation of dust exposure pathways for residential receptors are 

considered incomplete. Relevant compounds were not detected in shallow subsurface soil at AOI 

2. Therefore, the subsurface soil exposure pathway for future construction workers is considered

incomplete. The CSM for AOI 2 is presented on Figure 7-2.

7.1.3 AOI 3 

AOI 3 consists of five areas on the west side of the facility where firetruck maintenance and/or 

AFFF storage were known to occur from prior to 1988 to present-day. Any AFFF releases would 

have occurred on paved/concrete areas. AFFF released to the pavement or concrete could have 

run off to surface soil or infiltrated subsurface soil via cracks in pavement/concrete or joints 

between areas that are paved with different materials. 

Relevant compounds were detected below the SLs in surface soil at AOI 3. Site workers and

future construction workers could contact these constituents in surface soil via incidental ingestion 

and inhalation of dust. Therefore, the surface soil exposure pathways for site workers and future 

construction workers are potentially complete. The incidental ingestion and inhalation of dust 
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 7-3

exposure pathways for trespassers are considered potentially complete due to the potential for 

unauthorized access on Camp Guernsey. AOI 3 is located at the facility boundary near a 

residential neighborhood and school with athletic fields. Therefore, the incidental ingestion and 

inhalation of dust exposure pathways for the residential and recreational user receptors are 

considered potentially complete. Relevant compounds were not detected in shallow subsurface 

soil at AOI 3. Shallow subsurface soil was not collected from one boring (AOI03-04); however, 

relevant compounds were not detected from the mid-point soil sample (15 to 20 feet bgs) collected 

at this location. Therefore, based on the results of the three shallow subsurface soil samples, the 

subsurface soil exposure pathway for future construction workers is considered incomplete. The 

CSM for AOI 3 is presented on Figure 7-3. 

7.1.4 AOI 4 

AOI 4 comprises the outdoor wash rack west of the airfield. Firetrucks are not permitted to be 

washed in the outdoor wash rack area; however, firetrucks were observed being washed there at 

least once since 2009. Releases at AOI 1 may have occurred directly onto surface soil but may 

also have infiltrated to the subsurface soil via cracks in pavement or joints between areas that are 

paved with different materials. 

Relevant compounds were detected below the SLs in surface soil at AOI 4. Site workers and

future construction workers could contact these constituents in surface soil via incidental ingestion 

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

construction workers are potentially complete. The incidental ingestion and inhalation of dust 

exposure pathways for the trespasser is also considered potentially due to the potential for 

unauthorized access on Camp Guernsey. Residential structures are not located in the vicinity of

AOI 4; therefore, the incidental ingestion and inhalation of dust exposure pathways for the

residential receptors are considered incomplete. Relevant compounds were not detected in

shallow subsurface soil at AOI 4. Therefore, the subsurface soil exposure pathway for future 

construction workers is incomplete. The CSM for AOI 4 is presented on Figure 7-4. 

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 

Relevant compounds were detected above their SLs in groundwater sampled at CG-01. This 

location is in the observed upgradient direction of the AOI 1 footprint and may be indicative of 

potential unknown on- or off-facility sources; however, groundwater may also be affected by 

infiltration from the north end of the airfield or potentially by runoff that may convey downslope

from the airfield and AOI 1 during heavy precipitation. Therefore, detections in CG-01 are 

considered potentially attributable to AOI 1. Public, domestic, and facility drinking water is 

provided by supply wells located in the alluvial aquifer along the North Platte River, some of which 

are located within the facility boundary. PFOA was detected in a drinking water sample collected 

at Camp Guernsey. Based on the presence of the drinking water supply wells and completion 

depths within the unconfined alluvial aquifer, the direct ingestion exposure pathway for site worker,

trespasser, off-facility residential, and off-facility recreational user receptors is considered 

potentially complete. Depth to water measured at CG-01 in May 2022 during the SI was measured 

at 40.36 feet bgs. The industrial/commercial worker exposure scenario assumes excavation 

occurs at depths at or above 15 feet bgs. Based on the depth to groundwater at AOI 1, 

groundwater would likely not be encountered by construction workers, and the incidental ingestion 
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 7-4

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

is presented on Figure 7-1. 

7.2.2 AOI 2 

Relevant compounds were detected below their SLs in groundwater samples collected at AOI 2. 

The direct ingestion exposure pathway for site worker, trespasser, off-facility residential, and offfacility recreational user receptors is considered potentially complete for the same reasons 

established for AOI 1. Depth to water measured at AOI 2 in May 2022 during the SI was measured 

at 22.73 feet bgs; therefore, groundwater would likely not be encountered by construction 

workers, and the incidental ingestion exposure pathway for future construction workers is 

considered incomplete. The CSM for AOI 2 is presented on Figure 7-2. 

7.2.3 AOI 3 

Relevant compounds were detected below their SLs in groundwater samples collected at AOI 3. 

The direct ingestion exposure pathway for site worker, trespasser, off-facility residential, and offfacility recreational user receptors is considered potentially complete for the same reasons 

established for the other AOIs; therefore, the incidental ingestion exposure pathway for future 

construction workers is considered incomplete. The CSM for AOI 3 is presented on Figure 7-3. 

7.2.4 AOI 4 

PFOS was detected above the SL in groundwater AOI 4. The direct ingestion exposure pathway 

for site worker, trespasser, off-facility residential, and off-facility recreational user receptors is 

considered potentially complete for the same reasons established for the other AOIs. Depth to 

water measured at AOI 4 in May 2022 during the SI was measured at 19.72 feet bgs; therefore,

the incidental ingestion exposure pathway for future construction workers is considered 

incomplete. The CSM for AOI 4 is presented on Figure 7-4. 

7.3 Surface Water and Sediment Exposure Pathway

Surface water and sediment samples were not collected during the SI field mobilization at Camp 

Guernsey. 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 

Relevant compounds were detected in soil at AOI 1 and in soil and groundwater at nearby 

associated sample location CG-01. Several stormwater infiltration basins are located to the south 

and east of the airfield and the North Platte River is located to the south. PFAS are water soluble 

and can migrate readily from soil to surface water and sediment via leaching and run-off. It is 

possible the compounds detected in soil may have migrated to the infiltration basins or off-facility 

to the North Platte River via over land surface water flow or infiltration; therefore, the surface water 

and sediment exposure pathways via incidental ingestion for the site worker, future construction 

worker, trespasser, and off-facility recreational user receptors are considered potentially 

complete. Surface water from North Platte River is not directly used as drinking water in the 

vicinity, so the surface water ingestion exposure pathway for residents is considered incomplete.

The CSM for AOI 1 is presented on Figure 7-1. 
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 7-5

7.3.2 AOI 2 

Relevant compounds were detected in soil and groundwater at AOI 2. A stormwater infiltration 

basin is located just south of AOI 2, and drainage ditches may also channel water southeast from 

AOI 2 toward the North Platte River. Due to the water-soluble property of PFAS, it is possible the 

compounds detected in the surface soil at AOI 2 may have migrated via surface runoff or 

infiltration to the basin or the North Platte River. Therefore, the surface water and sediment 

ingestion exposure pathway for site worker, future construction worker, trespasser, or off-facility 

recreational users are considered potentially complete. The surface water exposure pathway for 

residents is considered incomplete for the same reasons established for AOI 1. The CSM for AOI 

2 is presented on Figure 7-2. 

7.3.3 AOI 3 and 4

Relevant compounds were detected in soil and groundwater at AOI 3 and AOI 4. It is possible that 

compounds detected in soil at these AOIs may have migrated via surface runoff or infiltration to 

the North Platte River, located to the south. The surface water and sediment exposure pathways 

via incidental ingestion for the site worker, future construction worker, trespasser, and off-facility 

recreational user receptors are considered potentially complete for the same reasons established 

for the other AOIs. The surface water exposure pathway for residents is considered incomplete

for the same reasons established for the other AOIs. The CSMs for AOI 3 and AOI 4 are presented 

on Figure 7-3 and Figure 7-4, respectively. 
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 7-6

THIS PAGE INTENTIONALLY BLANK
Media

SOURCE PATHWAY RECEPTOR

AOI 1

Annual Fire

Training

Activities, Fire

Truck Staging,

and AFFF

Storage

Subsurface

Soil

Human

Activities

Precipitation/

Run-Off

Leaching/

Infiltration

Airborne Soil

Particulate

Surface Soil

Surface

Water/

Sediment

Subsurface

Soil

Shallow

Groundwater

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

/ / /

LEGEND

Figure 7-1

Conceptual Site Model, AOI 1

Camp Guernsey, Guernsey, Wyoming

Potential

Off-Facility

Source Not

under

Control of

ARNG

Surface

Water

Surface

Water Flow

NOTES

1. The recreational users refer to off-site

receptors. Residential users refers to

both on-site and off-site receptors.

2. No active construction was observed

at the AOI during the SI field event.

Surface Soil

Site

Worker

Construction

Worker

Resident1Trespasser/

Recreational

User1

/ / / /

Trespasser/

Recreational

User1

Site

Worker

Construction

Worker Resident1

/ / / /

/

/ / / /

/ / / /

AECOM 

7-7
Media

SOURCE PATHWAY RECEPTOR

AOI 2

Fire Truck

Maintenance

and Cleaning

Subsurface

Soil

Human

Activities

Precipitation/

Run-Off

Leaching/

Infiltration

Airborne Soil

Particulate

Surface Soil

Surface

Water/

Sediment

Subsurface

Soil

Shallow

Groundwater

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

/ / /

LEGEND

Figure 7-2

Conceptual Site Model, AOI 2

Camp Guernsey, Guernsey, Wyoming

Potential

Off-Facility

Source Not

under

Control of

ARNG

Surface

Water

Surface

Water Flow

NOTES

1. The recreational users refer to offsite receptors. Residential users refers

to both on-site and off-site receptors.

2. No active construction was observed

at the AOI during the SI field event.

Surface Soil

Site

Worker

Construction

Worker

Resident1

/ / / /

Trespasser/

Recreational

User1

Site

Worker

Construction

Worker Resident1

/ / / /

/

/ / / /

Trespasser/

Recreational

User1

/ / / /

AECOM

7-8
Media

SOURCE PATHWAY RECEPTOR

AOI 3

Fire Truck

Maintenance,

AFFF Storage

Subsurface

Soil

Human

Activities

Precipitation/

Run-Off

Leaching/

Infiltration

Airborne Soil

Particulate

Surface Soil

Subsurface

Soil

Shallow

Groundwater

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

LEGEND

Figure 7-3

Conceptual Site Model, AOI 3

Camp Guernsey, Guernsey, Wyoming

Potential

Off-Facility

Source Not

under

Control of

ARNG

Surface

Water

Surface

Water Flow

Surface Soil

Trespasser/

Recreational

User1

Site

Worker

Construction

Worker Resident1

/ / /

/ / / /

/

/ / / /

/ / /

Site

Worker

Construction

Worker

Resident1

/ / / /

/

Surface

Water/

Sediment

NOTES

1. The recreational users refer to offsite receptors. Residential users refers

to both on-site and off-site receptors.

2. No active construction was observed

at the AOI during the SI field event.

Trespasser/

Recreational

User1

AECOM

7-9
Media

SOURCE PATHWAY RECEPTOR

AOI 4 Fire Truck

Cleaning

Subsurface

Soil

Human

Activities

Precipitation/

Run-Off

Leaching/

Infiltration

Airborne Soil

Particulate

Surface Soil

Surface

Water/

Sediment

Subsurface

Soil

Shallow

Groundwater

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

/ / /

LEGEND

Figure 7-4

Conceptual Site Model, AOI 4

Camp Guernsey, Guernsey, Wyoming

Potential

Off-Facility

Source Not

under

Control of

ARNG

Surface

Water

Surface

Water Flow

Surface Soil

Site

Worker

Construction

Worker

Resident1

/ / / /

Trespasser/

Recreational

User1

Site

Worker

Construction

Worker Resident1

/ / / /

/

NOTES

1. The recreational users refer to offsite receptors. Residential users refers

to both on-site and off-site receptors.

2. No active construction was observed

at the AOI during the SI field event.

Trespasser/

Recreational

User1

/ / / /

/ / / /

AECOM

7-10
Site Inspection Report

Camp Guernsey, Wyoming

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 9 March, 21 April to 6 May, and 3 June 2022 and 

consisted of source water sample collection, utility clearance, HSA borings, soil sample collection, 

permanent groundwater sampling point installation, low-flow groundwater sample collection, and 

land surveying. Field activities were conducted in accordance with the SI QAPP Addendum 

(AECOM, 2021), except as noted in Section 5.8. 

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

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

Table B-15 as follows. 

• Fifty-one (51) soil samples from thirty-one (31) locations;

• Seven (7) grab groundwater samples from seven (7) permanent groundwater sampling

points; and

• Twenty-seven (27) quality assurance QA/QC samples.

An SI is conducted when the PA determines an AOI exists based on probable use, storage, and/or 

disposal of PFAS-containing materials. The SI includes multi-media sampling at AOIs to 

determine whether or not a release has occurred. The SI may conclude further investigation is 

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

required. Additionally, the CSMs were refined to assess whether a potentially complete pathway 

exists between the source and potential receptors for potential exposure at the AOIs, which are 

described in Section 7. 

8.2 Outcome 

Based on the results of this SI, further evaluation under CERCLA is warranted in an RI for AOI 1

and AOI 4; no further evaluation is warranted for AOI 2 and AOI 3 at this time (see Table 8-1). 

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

exposure to site worker and residential drinking water receptors from AOI 1, AOI 2, AOI 3, and 

AOI 4 from sources on the facility resulting from historical DoD activities. Sample analytical 

concentrations collected during the SI were compared against the project SLs in soil and

groundwater, as described in Table 6-1. A summary of the results of the SI data relative to the 

SLs is as follows: 

• At AOI 1:

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

below their SLs.

• PFOA and PFHxS in groundwater exceeded their SLs. PFOA exceeded the 6 ng/L

SL, at a concentration of 79.2 ng/L at CG-01. PFHxS exceeded the 39 ng/L SL, at a

concentration of 438 J ng/L at CG-01. PFOS and PFBS were detected below their

SLs, and PFNA was not detected.
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 8-2

• Based on the results of the SI, further evaluation of AOI 1 is warranted in an RI.

• At AOI 2:

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

below their SLs. 

• In groundwater, PFOA, PFOS, PFBS, and PFHxS were detected below their SLs. 

The maximum detected concentration of the relevant compounds was PFBS at 18.9 

ng/L. PFNA was not detected in groundwater.

• Based on the results of the SI, no further evaluation of AOI 2 is warranted at this time.

• At AOI 3:

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

below their SLs. 

• In groundwater, PFOA, PFOS, PFBS and PFHxS were detected below their SLs. 

The maximum detected concentration of the relevant compounds was PFBS at 11.9

ng/L. PFNA was not detected in groundwater.

• Based on the results of the SI, no further evaluation of AOI 3 is warranted at this time.

• At AOI 4: 

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

below their SLs. 

• PFOS in groundwater exceeded the 4 ng/L SL, at a concentration of 4.21 ng/L at 

AOI04-01. PFOS, PFBS, and PFHxS were detected below their SLs. PFNA was not 

detected.

• Based on the results of the SI, further evaluation of AOI 4 is warranted in an RI.

Groundwater flow direction in the vicinity of Camp Guernsey was inferred to be predominantly 

southwest, toward the North Platte River. This inferred flow direction was used to determine SI 

sampling locations; however, the SI findings show an overall southeasterly groundwater flow 

direction throughout the Cantonment. Some uncertainty exists in the source of groundwater SL 

exceedances currently attributed to AOI 1 and AOI 4 as a result of the difference between the 

inferred and observed groundwater flow directions. The RI will address data gaps by refining the 

understood groundwater flow direction to help evaluate whether impacts observed during the SI 

may be attributable to other known or unknown release areas. 

AFFF was reportedly used during training activities exclusively at the Camp Guernsey Airfield 

(AOI 1), but the mechanism of release and specific release locations of the training activities is 

unknown. The position of AOI 1 atop a terrace, as well as the resistant cemented gravel unit

encountered during SI drilling, suggest that infiltration in the area may be limited and that releases 

at AOI 1 may transport via runoff to lower-lying areas during heavy precipitation events. This runoff 

may be the source of relevant PFAS compounds observed in groundwater at CG-01. However, 

uncertainty in the source exists due to the groundwater flow direction noted above, which 

suggests that potentially unidentified on- or off-facility sources may be another contributing factor. 

It is anticipated that the RI will address this data gap by evaluating areas upgradient from CG-01.

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 
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 8-3

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. 
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 8-4

Table 8-1: Summary of Site Inspection Findings and Recommendations

AOI Potential 

Release Area

Soil –

Source 

Area

Groundwater – 

Source Area Future Action

1 Camp Guernsey Airfield Proceed to RI 

2 Current Firetruck Maintenance 

Areas No further action

3 Historic Maintenance and 

Storage Areas No further action

4 Outdoor Wash Rack Proceed to RI

Legend:

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels
Site Inspection Report

Camp Guernsey, Wyoming

AECOM 9-1

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(PFOS) and Perfluorooctanoic Acid (PFOA) Impacted Sites ARNG Installations, Nationwide 

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

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