FINAL

Site Inspection Report

Army Aviation Support

Facility #2,

St. Cloud, Minnesota

Perfluorooctanesulfonic Acid (PFOS) and 

Perfluorooctanoic Acid (PFOA) Impacted Sites

ARNG Installations, Nationwide

March 2022 

Prepared for:

Army National Guard Bureau

111 S. George Mason Drive

Arlington, VA 22204

UNCLASSIFIED
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

THIS PAGE INTENTIONALLY BLANK
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM i

Table of Contents

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

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

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

1.2 SI Purpose .............................................................................................................. 1-1

2.0 Facility Background........................................................................................................ 2-1

2.1 Facility Location and Description ............................................................................ 2-1

2.2 Facility Environmental Setting................................................................................. 2-1

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

2.2.2 Hydrogeology ............................................................................................... 2-1

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

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

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

2.2.6 Critical Habitat and Threatened/Endangered Species.................................. 2-2

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

3.0 Summary of Area of Interest .......................................................................................... 3-1

3.1 AOI 1 – St. Cloud AASF #2..................................................................................... 3-1

4.0 Project Data Quality Objectives ..................................................................................... 4-1

4.1 Problem Statement ................................................................................................. 4-1

4.2 Goals of the Study .................................................................................................. 4-1

4.3 Information Inputs: .................................................................................................. 4-2

4.4 Study Boundaries ................................................................................................... 4-2

4.5 Analytical Approach ................................................................................................ 4-2

4.6 Data Usability Assessment ..................................................................................... 4-3

4.6.1 Precision ....................................................................................................... 4-3

4.6.2 Accuracy....................................................................................................... 4-4

4.6.3 Representativeness...................................................................................... 4-4

4.6.4 Comparability................................................................................................ 4-5

4.6.5 Completeness............................................................................................... 4-5

4.6.6 Sensitivity ..................................................................................................... 4-6

5.0 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 PFAS Sampling Equipment Acceptability ....................... 5-2

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

5.3 Temporary Well Installation and Groundwater Grab Sampling ............................... 5-3

5.4 Surface Water and Sediment Sampling.................................................................. 5-4

5.5 Investigation-Derived Waste ................................................................................... 5-4

5.6 Laboratory Analytical Methods................................................................................ 5-5

5.7 Deviations from QAPP Addendum.......................................................................... 5-5

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

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

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

6.3 AOI 1 – St. Cloud AASF #2..................................................................................... 6-2

6.3.1 Soil Analytical Results .................................................................................. 6-2
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM ii

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

6.3.3 Sediment Analytical Results ......................................................................... 6-2

6.3.4 Surface Water Analytical Results.................................................................. 6-2

6.3.5 Conclusions .................................................................................................. 6-2

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

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

7.1.1 AOI 1 – St. Cloud AASF #2 .......................................................................... 7-1

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

7.2.1 AOI 1 – St. Cloud AASF #2 .......................................................................... 7-2

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

7.3.1 AOI 1 – St. Cloud AASF #2 .......................................................................... 7-2

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

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

8.2 SI Goals Evaluation ................................................................................................ 8-1

8.3 Outcome ................................................................................................................. 8-2

9.0 References..................................................................................................................... 9-1
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM iii

Appendices

Appendix A Data Validation Reports 

Appendix B Field Documentation

B1. Log of Daily Notice of Field Activities

B2. Sampling Forms

B3. Nonconformance and Corrective Action Reports

B4. Investigation-Derived Waste Polygons

Appendix C Photographic Log

Appendix D TPP Meeting Minutes

Appendix E Boring Logs 

Appendix F Analytical Results

Appendix G Laboratory Reports

Figures

Figure 2-1 

Figure 2-2 

Figure 2-3 

Figure 2-4 

Figure 3-1 

Figure 5-1 

Figure 6-1 

Figure 6-2 

Figure 6-3 

Figure 6-4 

Figure 6-5 

Figure 7-1 

Site Location

Site Topography

Groundwater Features

Surface Water Features 

Area of Interest 

Site Inspection Sample Locations

PFOS Detections in Soil

PFOA Detection in Soil

PFAS Detections in Groundwater

PFOA and PFOS Detections in Sediment

PFOA and PFOS Detections in Surface Water

Conceptual Site Model, AOI 1

Tables

Table ES- 1 Screening Levels (Soil and Groundwater)

Table ES- 2 Summary of Site Inspection Findings

Table ES- 3 Site Inspection Recommendations

Table 5-1 Site Inspection Samples by Medium

Table 5-2 Soil Boring, Temporary Well, and Gauging Data

Table 6-1 Screening Levels (Soil and Groundwater) 

Table 6-2 PFAS Detections in Shallow Subsurface Soil

Table 6-3 PFAS Detections in Groundwater

Table 6-4 PFAS Detections in Surface Water

Table 8-1 Summary of Site Inspection Findings

Table 8-2 Site Inspection Recommendations
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM iv

Acronyms and Abbreviations

°C degrees Celsius

°F degrees Fahrenheit

μg/kg micrograms per kilogram

6:2 FTS 6:2 Fluorotelomer sulfonate acid

8:2 FTS 8:2 Fluorotelomer sulfonate acid

AASF Army Aviation Support Facility

AECOM AECOM Technical Services, Inc.

AFFF aqueous film forming foam

AOI area of interest

ARNG Army National Guard

bgs below ground surface 

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

CFR Code of Federal Regulations 

CoC chain of custody

CSM conceptual site model 

DA United States Department of the Army

DO dissolved oxygen

DoD Department of Defense

DPT direct-push technology

DQI data quality indicator

DQO data quality objective

DUA data usability assessment

DVR data validation report 

EIS extraction internal standards

ELAP Environmental Laboratory Accreditation Program 

EM Engineers Manual

ERB equipment rinsate blank

FedEx Federal Express

FRB field reagent blank

GPS global positioning system

HA Health Advisory 

HDPE high-density polyethylene

HEF high expansion foam 

IDW investigation-derived waste

ITRC Interstate Technology Regulatory Council

LC/MS/MS liquid chromatography mass spectrometry

LCS laboratory control sample

LCSD laboratory control sample duplicate

LOD limit of detection

LOQ limit of quantitation

MDL method detection limit
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM v

MDH Minnesota Department of Health 

MNARNG Minnesota Army National Guard

MNDNR Minnesota Department of Natural Resources

MS matrix spike 

MSD matrix spike duplicate

NELAP National Environmental Laboratory Accreditation Program

NEtFOSAA N-ethyl perfluorooctanesulfonamidoacetic acid

ng/L nanograms per liter

NMeFOSAA N-methyl perfluorooctanesulfonamidoacetic acid

ORP oxidation-reduction potential

OSD Office of the Secretary of Defense

PA Preliminary Assessment

PFAS per- and polyfluoroalkyl substances

PFBA perfluorobutyrate

PFBS perfluorobutanesulfonic acid

PFCs perfluorinated compounds

PFDA perfluorodecanoic acid

PFDoA perfluoroheptanoic acid

PFHpA perfluoroheptanoic acid

PFHxA perfluorohexanoic acid

PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

PFPeA perfluoropentanoic acid

PFTeDA perfluorotetradecanoic acid

PFTrDA perfluorotridecanoic acid

PFUdA perfluoroundecanoic acid

PID photoionization detector

PPE personal protective equipment

PQAPP Programmatic UFP-QAPP

PVC poly-vinyl chloride

QAPP Quality Assurance Project Plan

QC quality control

QSM Quality Systems Manual

RI Remedial Investigation

RPD relative percent differences

RSL regional screening level

SI Site Inspection

SL screening level 

SOP Standard Operating Procedure

TOC total organic carbon

TPP Technical Project Planning
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM vi

US United States

UFP Uniform Federal Policy

USACE United States Army Corps of Engineers

USCS Unified Soil Classification System

USEPA United States Environmental Protection Agency

USFWS United States Fish and Wildlife Service
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM ES-1

Executive Summary

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

Inspections (SIs) at per- and polyfluoroalkyl substances (PFAS)-impacted facilities at ARNG 

facilities nationwide. The objective of the SI at each facility is to identify whether there has been 

a release to the environment from the Areas of Interest (AOIs) identified in the PA and determine 

the presence or absence of perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), 

and perfluorobutanesulfonic acid (PFBS) at or above screening levels (SLs). This SI was 

performed at the Army Aviation Support Facility (AASF) #2 in St. Cloud, Minnesota. AASF #2 will 

be referred to as the “facility” throughout this document.

AASF #2 was constructed in 2007 on approximately 55 acres of land adjacent to the St. Cloud

Regional Airport, owned by the City of St. Cloud, and leased to the Minnesota ARNG (MNARNG). 

The lease agreement expires on 14 April 2104. AASF #2 facility includes an 80,000 square foot 

hangar for the operation, maintenance, and repair of MNARNG rotary-winged aircraft, 

administrative offices, and classrooms. The PA report (AECOM, 2019a) identified three potential 

PFAS releases areas grouped together into AOI 1. The release of Jet-X high expansion foam 

(HEF) had occurred from the fire suppression system at AASF #2 in 2009, 2011, and 2013. After 

the releases in 2009 and 2011, HEF was washed to the sanitary sewer and is, therefore, not 

suspected to have impacted AOI 1. However, after the release in June 2013, HEF was washed 

out of both sides of the hangar and plowed into the northeast and southwest detention ponds by 

the MNARNG. In addition, rotary-winged aircraft were washed on the northeast side of the hangar 

following the release, and the wash water was allowed to dissipate in the northeast detention 

pond. Furthermore, without knowledge of the precise chemical constituents of the HEF used at 

the facility, the ARNG decided to investigate AASF#2 as if the released HEF contained PFAS. 

To fulfill the project Data Quality Objectives (DQOs) set forth in the approved SI Quality Assurance 

Project Plan (QAPP) Addendum (AECOM, 2019b), samples were collected and analyzed for a 

subset of 18 PFAS by liquid chromatography with tandem mass spectrometry (LC/MS/MS) 

compliant with Quality Systems Manual (QSM) 5.1 Table B-15. The 18 PFAS analyzed as part of 

the ARNG SI program are specified in Section 5.9 of this Report. 

The Department of Defense (DoD) has adopted a policy to retain facilities in the Comprehensive 

Environmental Response, Compensation, and Liability Act (CERCLA) process based on risk-based 

SLs for soil and groundwater, as described in a memorandum from the Office of the Secretary of 

Defense (OSD) dated 15 October 2019 (Assistant Secretary of Defense, 2019). The ARNG PFAS 

SIs follow this DoD policy and, should the maximum facility concentration for sampled media exceed 

the SLs, the facility will proceed to a Remedial Investigation (RI), the next phase under CERCLA. 

The SLs apply to three compounds, PFOA, PFOS, and PFBS, for both soil and groundwater, as 

presented in Table ES-1. All other results presented in this report are considered informational in 

nature and serve as an indication as to whether soil, groundwater, sediment, and surface water 

contain or do not contain the 18 PFAS analyzed within the boundaries of the facility. 

Sample chemical analytical concentrations were compared against the project SLs as described in 

Table ES-1. A summary of the results of the SI data relative to the SLs is as follows: 

• PFOA and PFOS were detected in groundwater in AOI 1 near the facility boundary, with 

maximum detected concentrations of 2.74 J ng/L and 1.85 J ng/L, respectively. PFOA and 

PFOS detection in groundwater were below the SLs. PFBS was not detected in groundwater 

at AOI 1.

• PFOA, PFOS, and PFBS were not detected in soil at AOI 1.

Table ES-2 summarizes the SI results for soil and groundwater. Based on the conceptual site 

models (CSMs) developed and revised in light of the SI findings, there is limited potential for 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM ES-2

exposure to residential drinking water receptors caused by DoD activities at or adjacent to the 

facility. 

Table ES-3 summarizes the rationale used to determine if an AOI should be considered for further 

investigation under CERCLA and undergo an RI. Based on the results of this SI, no further action 

is recommended for AOI 1 at AASF #2 at this time.
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM ES-3

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

Analyte

Residential

(Soil)

(μg/kg)a,b

0-2 feet bgs

Industrial/ Commercial 

Composite Worker

(Soil)

(μg/kg)a,b

2-15 feet bgs

Tap Water

(Groundwater) 

(ng/L)a,b

PFOA 130 1,600 40

PFOS 130 1,600 40

PFBS 130,000 1,600,000 40,000

Notes:

a.) Assistant Secretary of Defense, 2019. Risk Based Screening Levels Calculated for PFOS, PFOA, PFBS in 

Groundwater and Soil using United States Environmental Protection Agency’s (USEPA’s) Regional Screening Level

(RSL) Calculator with Hazard Quotient (HQ)=0.1. 15 October 2019.

Table ES- 2: Summary of Site Inspection Findings

AOI Potential PFAS 

Release Area

Soil – 

Source Area

Groundwater – 

Source Area

Groundwater –

Facility 

Boundary

1 St. Cloud AASF #2

Legend:

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected

Table ES- 3: Site Inspection Recommendations

AOI Description Rationale Future Action

1 St. Cloud AASF #2 Detections in groundwater and surface water. No 

exceedances of the SLs in soil or groundwater. No further action
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM ES-4

THIS PAGE INTENTIONALLY BLANK
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 1-1

1.0 Introduction

1.1 Project Authorization

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

(PAs) and Site Inspections (SIs) for Perfluorooctanesulfonic acid (PFOS) and Perfluorooctanoic 

acid (PFOA) at impacted facilities, ARNG Installations, Nationwide. This work is supported by the 

United States (US) Army Corps of Engineers (USACE) Baltimore District and their contractor, 

AECOM Technical Services, Inc. (AECOM), under Contract Number W912DR-12-D-0014, Task 

Order W912DR17F0192, issued 11 August 2017. The ARNG performed this SI at the Army 

Aviation Support Facility (AASF) #2, in St. Cloud, Minnesota. AASF #2 will be referred to as the 

“facility” throughout this document.

The SI project elements were performed in compliance with Comprehensive Environmental 

Response, Compensation, and Liability Act (CERCLA; 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 the US 

Department of the Army requirements and guidance for field investigations including specific 

requirements for sampling for PFOA, PFOS, and perfluorobutanesulfonic acid (PFBS), and the 

group of related compounds known in the industry as per- and poly-fluoroalkyl substances 

(PFAS). The term PFAS is used throughout this report to encompass all PFAS chemicals being 

evaluated, including PFOA, PFOS, and PFBS, which are the key components of the suspected 

releases being evaluated, and the other 15 related compounds listed in the task order. 

1.2 SI Purpose

A PA was performed at AASF #2 (AECOM, 2019a) that identified three potential PFAS release 

areas which were grouped into one Area of Interest (AOI). The objective of the SI is to identify 

whether there has been a release to the environment from the AOIs and determine the presence 

or absence of PFOA, PFOS, and PFBS at or above screening levels (SLs). 

As stated in the Federal Facilities Remedial Site Inspection Summary Guide (USEPA, 2005), an 

SI has five goals: 

1. Develop information to potentially eliminate a release from further consideration because 

it is determined that it poses no significant threat to human health or the environment;

2. Determine the potential need for a removal action;

3. Collect or develop data to evaluate potential release;

4. Collect data to better characterize the release for more effective and rapid initiation of a 

Remedial Investigation (RI), if determined necessary; and

5. Collect data to determine whether the release is more than likely the result of activities 

associated with the Department of Defense (DoD).

In addition to the USEPA-identified goals of an SI, the ARNG SI also identifies whether there are 

potential off-facility PFAS sources. 

 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 1-2

THIS PAGE INTENTIONALLY BLANK
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 2-1

2.0 Facility Background

2.1 Facility Location and Description 

AASF #2 is along US Highway 10, in Haven Township, Sherburne County, Minnesota (Figure 

2-1), approximately 4 miles southeast of St. Cloud, Minnesota, and 60 miles northwest of 

Minneapolis-St. Paul.

AASF #2 was constructed in 2007 on approximately 55 acres of land adjacent to the St. Cloud 

Regional Airport, owned by the City of St. Cloud, and leased to the Minnesota ARNG (MNARNG). 

The lease agreement expires on 14 April 2104. AASF #2 facility includes an 80,000 square foot 

hangar for the operation, maintenance, and repair of MNARNG rotary-winged aircraft, 

administrative offices, and classrooms

2.2 Facility Environmental Setting

AASF #2 lies within the Upper Mississippi River Basin, which encompasses several land 

tributaries to the Mississippi River. The area is relatively flat, with small variations in elevation. 

The elevation of the facility is approximately 1,030 feet above mean sea level. The surrounding 

area is covered by cropland, wooded area, and wetlands. 

2.2.1 Geology

AASF #2 is situated in the Anoka Sand Plain Subsection of the Eastern Broadleaf Forest Province 

as defined by the Minnesota Department of Natural Resources (MNDNR) Ecological 

Classification System (Sherburne County Planning & Zoning Department, 2011). The Anoka Sand 

Plain is a sandy lake plain formed from runoff and repeated incursions of the sea (Cummins and 

Grigal, 1981). Bedrock in the area consists of gently dipping layers of sandstone, shale, and 

carbonate rocks that range in thickness from 50 feet to greater than 200 feet (MNDNR, 2017). 

The bedrock ranges in age from Archean granites to Upper Mesozoic Cretaceous sediments 

(Cummins and Grigal, 1981). The bedrock is underlain by sedimentary rock formed by volcanism 

from the Precambrian Age to the Ordovician Age, including the Hinckley Sandstone and Fond du 

Lac Formation (MNDNR, 2017). Granite plutons from the East-Central Batholith are abundant in 

the region and are quarried for buildings and monuments (Cummins and Grigal, 1981). At the 

surface, the area is aggregate and defined by remnants of glaciation including moraine, drumlins, 

eskers, kames, and outwash plains with deposited deep layers of glacial till. Glacier-formed 

depressions have formed wetlands and many of the state's modern lakes and rivers. 

2.2.2 Hydrogeology

AASF #2 is within the Central Groundwater Province as defined by the MNDNR (Sherburne 

County Planning & Zoning Department, 2011) and drained on the northeast side by the Town of 

Parent-Elk Watershed and on the southwest side by the County Ditch Number Three Watershed. 

Groundwater is drawn from sand and gravel aquifers and from deeper fractured and weathered 

bedrock or sedimentary rock. Depth to groundwater in the area ranges from 7 to 28 feet below 

ground surface (bgs), although wells that are closer to lakes, streams, rivers, and wetlands are 

shallower (Sherburne County Planning & Zoning Department, 2011). Groundwater flow is 

generally to the south and laterally toward larger creeks and rivers (Figure 2-3). Aquifer recharge 

is predominantly through infiltration of precipitation, although some recharge occurs from open 

water sources (MNDNR, 2017). 

No potable water wells are located within the boundary of AASF #2; however, several domestic 

and irrigation wells are located within 4 miles downgradient of the facility (Figure 2-3). These 

wells also include private and residential wells observed during the visual site inspection. The 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 2-2

majority of groundwater use in the area is for irrigation (MNDNR 2017). Drinking water for AASF

#2 is supplied by the City of St. Cloud, which uses the Mississippi River as its drinking water 

source (City of St. Cloud, 2011). 

2.2.3 Hydrology

Sherburne County has 125 lakes, most of which are less than 20 feet deep and 493 miles of rivers 

and streams (Sherburne County Planning & Zoning Department, 2011). The largest lake near 

AASF #2 is Donovan Lake, approximately 2 miles to the north, and the largest river is the 

Mississippi River, located approximately 5 miles west of AASF #2 (Figure 2-4). 

AASF #2 has detention ponds on both the northeastern and southwestern sides of the ramps that 

are flanked by wetlands and collect runoff from AASF #2. The detention ponds are approximately 

3 feet deep and seeded with vegetation. Swales in both detention ponds carry intermittent surface 

water to storm sewers and the Elk River. The Elk River runs parallel to the Mississippi River before 

converging at the city of Elk River. Other regional surface water features include small lakes, 

tributaries, and wetlands.

2.2.4 Climate

The climate of St. Cloud consists of hot, humid summers, and cold winters with moderate to heavy 

snowfall. Seasonally, temperatures vary from summer highs of 82 degrees Fahrenheit (°F) to 

winter lows of 2°F (World Climate, 2018). The average temperature is 42.85°F. Average 

precipitation is 27.72 inches of rain and 47 inches of snow (World Climate, 2018). The area is 

subject to severe storms and occasional tornadoes. The prevailing wind varies from north to 

south, averaging 8 to 12 miles per hour.

2.2.5 Current and Future Land Use

AASF #2 is a controlled access facility with public roads and is adjacent to the St. Cloud Regional 

Airport. The St. Cloud Regional Airport is owned and operated by the City of St. Cloud and 

provides private, commercial, corporate, cargo, and military air service. Future infrastructure 

improvements, land acquisitions, and land use controls are anticipated in the area, as significant 

urban development along the Interstate-94/Highway 10 corridor continues due to the migration of 

businesses and residents from the Twin Cities (MnDot, 2006).

2.2.6 Critical Habitat and Threatened/Endangered Species 

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

species in Sherburne County, Minnesota (US Fish and Wildlife Service [USFWS], 2019): 

• Insects: Rusty patch bumble bee, Bombus affinis (endangered), and 

• Mammal: Northern Long-Eared bat, Myotis septentrionalis (threatened). 

No critical habitats were identified within the boundary of the facility. 

2.3 History of PFAS Use 

Releases of Jet-X high expansion foam (HEF) have occurred from the fire suppression system at 

AASF #2 in 2009, 2011, and 2013. After the releases in 2009 and 2011, HEF was washed to the 

sanitary sewer and is, therefore, not suspected to have impacted AOI 1. However, after the 

release in June 2013, HEF was washed out of both sides of the hangar and plowed into the 

northeast and southwest detention ponds by the MNARNG. In addition, rotary-winged aircraft 

were washed on the northeast side of the hangar following the release, and the wash water was 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 2-3

allowed to dissipate in the northeast detention pond. Photographs provided by the MNARNG 

show HEF on the ground surface throughout the entire facility boundary and on the AASF #2

building following the June 2013 release. 

Drinking water for the facility is supplied by the City of St. Cloud; however, domestic water supply 

wells and private, residential wells are present to the southwest and northeast of the facility. 

Groundwater flow at AASF #2 is predominantly to the south-southwest. A description of the AOI 

is presented in Section 3. 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 2-4

THIS PAGE INTENTIONALLY BLANK
CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

JZ

5/27/2021

5/27/2021

NOTES Site Inspection for PFAS at St. Cloud AASF #2, MN

1:63,360

5/27/2021 ­ Figure 2-1

PM CM 5/27/2021

12420 Milestone Center Drive

Germantown, MD 20876

Facility Location

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

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

C:\Users\stankevichm\OneDrive - AECOM Directory\ARNG_PFAS_GIS_60552172\MXDs\MN\StCloud_Figures\StCloud_SI_Figures\SI_Report\Fig_2-1_StCloud_Facility_Location.mxd

Legend

Facility Boundary

0 0.5 1 2

Miles

St. Cloud AASF

^_

AECOM 2-5
CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

JP

5/27/2021

5/27/2021

NOTES Site Inspection for PFAS at St. Cloud AASF #2, MN

1:31,680

5/27/2021 ­ Figure 2-2

PM CM 5/27/2021

12420 Milestone Center Drive

Germantown, MD 20876

Site Topography

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

increment P Corp., GEBCO, USGS, FAO, NPS, NRCAN,

Q:\Projects\ENV\GEARS\GEO\ARNG PFAS\900-CAD-GIS\920-GIS or Graphics\MXD\MN\StCloud_SI_Figures\

Legend

Facility Boundary

0 0.25 0.5 1

Miles

AECOM 2-6
!5

!5

!P

!P

!P

!P

!P

!P

A!

!P

!P

!P

A!

!5

!P

!P

!P 

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

A!

!5

!5

!P

!P

!P

!P

!P

!P

!P

!P

!5

!P

!P

!P

!5

A!

!P

!P

!P

!P

!P

!P

!5

!5

!P

!P

A!

!P

!P

!P

!P

!P

!P

!P

!5

A!

!5

!5

!5

!P

!P

!P

!5

!P !5

!P

!5

!5

!5

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!5

!P

!P

A!

!5

!P

!P

!P

!5

!5

!P

!P

!P

A!

!5

!5

!P

!P!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!5

!P

!P

!P

!P

A!

!P

!5

!P

!P

!5

A!

A! A!

!P

!5

!P

!P

!5

!P

!P

!P

!5

!P

!5

!P

!5

!P

!P !P

!P

!P !P

!P

!P

!P

!P

!P

!P

!P

!P

!5

!5

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!5

!5

!P

!5

!P !P

!5

!P

!5

!P

!P

!5

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!5

!P

!5

!P

!P

!P

!P

!P

!P

!P

!5

!5

!P

!P

!5

!P

!5

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P

!P !P

!5

!5

!P

!P

!P

A!

!P

A!

!P

!P

!P

A!

!P

!5

!P

!5

!P

!P

Elk Ri v er

County Ditch Number Three

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

JZ

5/27/2021

5/27/2021

NOTES Site Inspection for PFAS at St. Cloud AASF #2, MN

1:31,680

5/27/2021 ­ Figure 2-3

PM CM 5/27/2021

12420 Milestone Center Drive

Germantown, MD 20876

Groundwater Features

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

Geographics, CNES/Airbus DS, USDA, USGS,

Q:\Projects\ENV\GEARS\GEO\ARNG PFAS\900-CAD-GIS\920-GIS or Graphics\MXD\MN\StCloud_SI_Figures\

Legend

Facility Boundary

Water Body

Wetland

River/Stream

Canal/Ditch

Inferred Groundwater

Flow Direction

Wells

!P Domestic

!P Commercial

!5 Industrial

!5 Irrigation

A! Monitoring/Observation

A! Other

Geology

Granite

Gray granodiorite to

granite intrusions

0 0.25 0.5 1

Miles

AECOM 2-7
Elk River

County Ditch Number Three

Fish

Creek-Mississippi

River Watershed

County Ditch

Number Three

Watershed

Town of Parent-Elk

River Watershed

Rice Creek

Watershed

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

JP

5/27/2021

5/27/2021

NOTES Site Inspection for PFAS at St. Cloud AASF #2, MN

1:31,680

5/27/2021 ­ Figure 2-4

PM CM 5/27/2021

12420 Milestone Center Drive

Germantown, MD 20876

Surface Water Features

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

Geographics, CNES/Airbus DS, USDA, USGS,

Q:\Projects\ENV\GEARS\GEO\ARNG PFAS\900-CAD-GIS\920-GIS or Graphics\MXD\MN\StCloud_SI_Figures\

Legend

Facility Boundary

Water Body

Wetland

River/Stream

Canal/Ditch

Surface Water Flow

Direction

0 0.25 0.5 1

Miles

AECOM 2-8
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 3-1

3.0 Summary of Area of Interest 

This section presents a summary of each potential PFAS release area by AOI. Based on the PA 

findings, one AOI was identified at the facility. AOI 1 encompasses the entire area within the AASF

#2 boundary (Figure 3-1). A summary of the AOI is presented below.

3.1 AOI 1 – St. Cloud AASF #2 

AOI 1 encompasses the entire area within the AASF #2 property boundary. Releases of HEF 

occurred from the fire suppression system at AASF #2 in 2009, 2011, and 2013. The HEF from 

the 2009 and 2011 releases was washed to the sanitary sewer and is not suspected to have 

impacted AASF #2. The sanitary sewer flows to the St. Cloud Wastewater Treatment Facility in 

St. Cloud, Minnesota. However, after the release in June 2013, HEF was washed out of both 

sides of the hangar and plowed into the northeast and southwest detention ponds by the 

MNARNG. In addition, rotary-winged aircraft were washed on the northeast side of the hangar 

following the release, and the wash water was allowed to dissipate in the northeast detention 

pond. There was a low probability of the HEF containing PFAS, however, absent knowledge of 

the precise chemical constituents of the HEF used at the facility, the ARNG decided to investigate 

St Cloud AASF#2 as if aqueous film forming foam (AFFF) containing PFAS had been used and 

released. Photographs provided by the MNARNG show HEF on the ground surface throughout 

the entire facility boundary and on the AASF #2 building following the June 2013 release. No 

remediation activities have occurred at this location (AECOM, 2019a). 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 3-2

THIS PAGE INTENTIONALLY BLANK
!P

!P

!P

!P

!P

!P

!5

!P

!5

!5

!P !P

!P

!P

!P

!P

!P

!P 

!P

!P

!P

!P

!5

!P

!P

!P

!P

!P

!P

!P !P

!P 

!P

!P

!P

!P

!P 

A!

A!

!P

A!

Northeastern

Detention Pond

Southwestern

Detention Pond

City of St. Cloud

Station 4

Elk River

County Ditch

Number Three

Watershed

Town of Parent-Elk

River Watershed

Hangar Release

City of St. Cloud FTA

AOI 1

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

JZ

5/27/2021

5/27/2021

NOTES Site Inspection for PFAS at St. Cloud AASF #2, MN

1:14,400

5/27/2021 ­ Figure 3-1

PM CM 5/27/2021

12420 Milestone Center Drive

Germantown, MD 20876

Area of Interest

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

Geographics, CNES/Airbus DS, USDA, USGS,

Q:\Projects\ENV\GEARS\GEO\ARNG PFAS\900-CAD-GIS\920-GIS or Graphics\MXD\MN\StCloud_SI_Figures\

Legend

Area of Interest

Potential PFAS Release

Facility Boundary

Water Body

River/Stream

Canal/Ditch

Surface Water Flow Direction

Inferred Groundwater Flow Direction

!P Domestic

!5 Irrigation

A! Monitoring/Observation

A! Other

0 600 1,200 2,400

Feet

A!

City of St. Cloud

 Station 4

County Ditch

Number Three

Watershed

City of St.

Cloud FTA

AECOM 3-3
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 3-4

THIS PAGE INTENTIONALLY BLANK
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 4-1

4.0 Project Data Quality Objectives

Project Data Quality Objectives (DQOs) are qualitative and quantitative statements that specify 

the quality of data and define the level of certainty required to support the project decision-making

process. The specific DQOs established for this facility are described below. These DQOs were 

developed in accordance with the USEPA’s seven-step iterative process (USEPA, 2006). 

4.1 Problem Statement

The following problem statement was developed during project planning:

The presence of PFAS, which may pose a risk to human health or the environment, in environmental 

media at the facility is currently unknown. PFAS are classified as emerging environmental 

contaminants that are garnering increasing regulatory interest due to their potential risks to human

health and the environment. The regulatory framework for managing PFAS at both the federal and 

state level continues to evolve. As such, without knowledge of the precise chemical constituents of 

the HEF used at the facility, the ARNG decided to investigate AASF#2 as if the released HEF 

contained PFAS. 

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 Office of the Secretary of 

Defense (OSD) dated 15 October 2019 (Assistant Secretary of Defense, 2019). The ARNG 

program under which this SI was performed follows this DoD policy. Should the maximum facility 

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 three compounds: PFOS, PFOA, and PFBS. The SLs are presented in Section 6.1 of 

this Report. 

The following quotes from the US Department of the Army (DA) policy documents form the basis 

for this project (DA, 2016; DA, 2018): 

• “The Army will research and identify locations where PFOS- and/or PFOA-containing 

products, such as AFFF, are known or suspected to have been used. Installations shall 

coordinate with installation/facility fire response or training offices to identify AFFF use or 

storage locations. The Army will consider fire training areas, AFFF storage locations, 

hangars/buildings with AFFF suppression systems, fire equipment maintenance areas, and 

areas where emergency response operations required AFFF use as possible source areas. 

In addition, metal plating operations, which used certain PFOS-containing mist 

suppressants, shall be considered possible source areas.” 

• “Based on a review of facility records...determine whether a CERCLA PA is appropriate for 

identifying PFOS/PFOA release sites. If the PA determines a PFOS/PFOA release may 

have occurred, a CERCLA SI shall be conducted to determine presence/absence of 

contamination.” 

• “Identify sites where perfluorinated compounds (PFCs) are known or suspected to have 

been released, with the priority being those sites within 20 miles of the public systems that 

tested above USEPA HA levels” (USEPA, 2016a; USEPA, 2016b). 

4.2 Goals of the Study

The following goals were established for this SI:

1. Determine the presence or absence of PFOA, PFOS, and PFBS at or above SLs.
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 4-2

2. Develop information to potentially eliminate a release from further consideration because 

it is determined that it poses no significant threat to human health or the environment.

3. Determine the potential need for a removal action. 

4. Collect data to better characterize the release areas for more effective and rapid initiation 

of a RI.

5. Identify within 4 miles of the installation other potential PFAS sources (fire stations, major 

manufacturers, other DoD facilities) and receptors, including both groundwater and 

surface water receptors, to determine whether the ARNG is the likely source of PFAS, or 

whether there is an off-facility source of PFAS responsible for installation detections of 

PFAS (USEPA, 2005).

6. Determine whether a potentially complete pathway exists between the source and 

potential receptors and whether ARNG is the likely source of the contamination. 

4.3 Information Inputs:

Primary information inputs for the SI include the following: 

• The PA for AASF #2 (AECOM, 2019a); 

• Analytical data from groundwater, soil, surface water, and sediment samples collected as 

part of this SI in accordance with the site-specific Uniform Federal Policy (UFP)-Quality 

Assurance Project Plan (QAPP) Addendum (AECOM, 2019b); and

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

parameters measured at the time of sampling. 

4.4 Study Boundaries

The scope of the SI was bounded by the property limits of the facility (Figure 2-2). Off-site sampling 

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

will be notified, and necessary rights of entry will be obtained by ARNG with property owner(s). 

4.5 Analytical Approach

Samples were analyzed by Pace Gulf Coast, accredited under the 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 and decision rules as defined in the SI QAPP Addendum (AECOM, 2019b). 

Decision rules were developed for groundwater and soil, and then applied to all data collected. 

These rules governed response actions based on the results of the SI sampling effort.

The decision rules described in the Worksheet #11 of the QAPP Addendum identify actions based 

on the following:

Groundwater:

• Is there a human receptor within 4 miles of the facility? 

• What is the concentration of PFOA, PFOS, and PFBS at the potential release areas?

• What is the concentration of PFOA, PFOS, and PFBS at the facility boundary upgradient 

and downgradient of the potential release areas?
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 4-3

• What does the conceptual site model (CSM) suggest in terms of source, pathway, and 

receptor? 

Soil:

• What is the concentration of PFOA, PFOS, and PFBS in shallow surface soil (0 to 2 feet 

bgs)?

• What is the concentration of PFOA, PFOS, and PFBS in deep soil (i.e., capillary fringe)?

• What does the CSM suggest in terms of source, pathway, and receptor? 

Soil, groundwater, surface water, and sediment samples were collected from the potential PFAS 

release areas within AOI 1. Depth to groundwater was observed to range from 3.45 to 13.22 feet 

bgs. 

4.6 Data Usability Assessment

The Data Usability Assessment (DUA) is an evaluation at the conclusion of data collection 

activities that uses the results of both data verification and validation in the context of the overall 

project decisions or objectives. Using both quantitative and qualitative methods, the assessment 

determines whether project execution and the resulting data have met installation-specific DQOs. 

Both sampling and analytical activities are considered to assess whether the collected data are 

of the right type, quality, and quantity to support the decision-making.

Data Quality Indicators (DQIs) (Precision, Accuracy, Representativeness, Comparability, 

Completeness and Sensitivity) are important components in assessing data usability. These DQIs 

were evaluated in the subsequent sections and demonstrate that the data presented in this SI 

report are of high quality. Although the SI data are considered reliable, some degree of uncertainty 

can be associated with the data collected. Specific factors that may contribute to the uncertainty 

of the data evaluation are described below. The Data Validation Report (DVR) (Appendix A) 

presents explanations for all qualified data in greater detail.

4.6.1 Precision

Precision is the degree of agreement among repeated measurements of the same characteristic 

on the same sample or on separate samples collected as close as possible in time and place. 

Field sampling precision is measured with the field duplicate relative percent differences (RPD); 

laboratory precision is measured with calibration verification, internal standard recoveries, 

laboratory control spike (LCS) and matrix spike (MS) duplicate RPD.

Extraction internal standards (EIS) were added by the laboratory during sample extraction to 

measure relative responses of target analytes and used to correct for bias associated with matrix 

interferences and sample preparation efficiencies, injection volume variances, mass spectrometry 

ionization efficiencies, and other associated preparation and analytical anomalies. Several field 

samples displayed EIS area counts less than the QC limit of 50%. The positive field sample results 

associated with EIS area counts less than the QC limit were qualified “J+”, while non-detects were 

qualified “UJ”. The qualified results should be considered usable as estimated values with a 

positive bias. The results associated with EIS recoveries less than 20% were included in the data 

set because the PFAS compounds are quantitated based on a normalized internal standard 

recovery, and in the site matrix spike pairs with low area counts the target compounds were shown 

to display acceptable recoveries. The qualified field sample results associated with EIS area 

counts less than 20% were not applied to compounds PFOA, PFOS, and PFBS in any media and 

were treated in the data set as true negatives.
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 4-4

Calibration verifications were performed routinely to ensure that instrument responses for all 

calibrated analytes were within established QC criteria. All calibration verifications were within the 

project established precision limits presented in the QAPP Addendum (AECOM, 2019b). 

Laboratory control spike/laboratory control spike duplicate (LCS/LCSD) pairs were prepared by 

addition of known concentrations of each analyte in a matrix-free media known to be free of target 

analytes. LCS/LCSD pairs were analyzed for every analytical batch to demonstrate the ability of 

the laboratory to detect similar concentrations of a known quantity in matrix-free media. The 

LCS/LCSD samples were within the project established precision limits presented in the QAPP 

Addendum (AECOM, 2019b). 

Matrix spike/matrix spike duplicate (MS/MSD) samples were prepared, analyzed, and reported 

for all preparation batches. MS/MSD samples demonstrated that the analytical system was in 

control for the matrix being tested. MS/MSD samples were submitted to the laboratory for analysis 

at a rate of 5%. The MS/MSD performed on parent sample AOI1-SB05 displayed a RPD greater 

than the upper QC limit of 30% for PFTrDA. The parent sample result associated with this positive 

bias was non-detect, therefore, no data qualifying action was required.

Field duplicate samples were collected at a rate of 10% to assess the overall sampling and 

measurement precision for this sampling effort. The field duplicate samples were analyzed for 

PFAS and general chemistry parameters. The field duplicate samples were within the project 

established precision limits presented in the QAPP Addendum (AECOM, 2019b). 

4.6.2 Accuracy

Accuracy is a measure of confidence in a measurement. The smaller the difference between the 

measurement of a parameter and its "true" or expected value, the more accurate the 

measurement. The more precise or reproducible the result, the more reliable or accurate the 

result. Accuracy is measured through percent recoveries in the LCS/LCSD, MS/MSD, and 

surrogates.

LCS/LCSD samples were prepared by addition of known concentrations of each analyte in a 

matrix free media known to be free of target analytes. LCS/LCSD samples were analyzed for 

every analytical batch and demonstrated that the analytical system was in control during sample 

preparation and analysis, with one exception. The LCS/LCSD pairs prepared in batch 669971 

displayed a percent recovery greater than the upper QC limit of 130% for NEtFOSAA and PFTrDA. 

The associated field sample results were non-detect, therefore, no data qualifying action was 

required. 

MS/MSD samples were prepared, analyzed, and reported at a rate of 5%. MS/MSD samples 

demonstrated that the analytical system was in control for the matrix being tested, with a limited 

number of exceptions. The MS/MSD performed on field sample AOI1-SB05 displayed percent 

recoveries greater than the upper QC limit of 130% for PFTrDA. The associated field sample 

results were non-detect, therefore, no data qualifying action was required. 

4.6.3 Representativeness

Representativeness qualitatively expresses the degree to which data accurately reflect site 

conditions. Factors that affect the representativeness of analytical data include appropriate 

sample population definitions, proper sample collection and preservation techniques, analytical 

holding times, use of standard analytical methods, and determination of matrix or analyte 

interferences. 

Relating to the use of standard analytical methods, the laboratory followed the method as 

established in PFAS by LC/MS/MS Compliant with QSM 5.1 Table B-15, including the specific 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 4-5

preparation requirements (i.e. ENVI-Carb or equivalent used), mass calibration, spectra, all the 

ion transitions identified in Table B-15 were monitored, standards that contained both branched

and linear isomers when available were used, and isotopically labeled standards were used for 

quantitation.

Field QC samples were collected to assess the representativeness of the data collected. Field 

duplicates were collected at a rate of 10% for all field samples, while MS/MSD samples were 

collected at a rate of 5%. All preservation techniques were followed by the field staff, and all 

technical and analytical holding times were met by the laboratory. The laboratory used approved 

standard methods in accordance with the QAPP Addendum (AECOM, 2018e) for all analyses.

Instrument blanks and method blanks were prepared by the laboratory in each batch as a negative 

control. A limited number of PFAS instrument blanks and method blanks displayed detections 

greater than the detection limit for multiple target analytes. In total, one field sample result for 

PFOS was qualified “U” during data validation due to a detection in the associated method blank. 

The reported field sample result value was adjusted to be equal to the limit of detection (LOD). 

The result is usable as qualified but should be considered a false positive and treated as nondetect.

Field blanks and equipment blanks were also collected for groundwater and soil samples. All 

equipment blanks and field blanks were non-detect for all target analytes.

A sample of the water used for decontamination of the drill rig was collected in advance of the 

field effort. The decontamination sample, “POTABLE WATER”, displayed a detection for PFBA 

greater than the detection limit at 4.27 ng/L. The positive associated field sample results that 

displayed concentrations less than five times the detection found in the decontamination sample 

were qualified “U.” The results are usable as qualified but should be considered false positives 

and treated as non-detect.

Overall, the data are usable for evaluating the presence or absence of PFAS at the Site. Sufficient 

usable data were obtained to meet the objectives of the SI.

4.6.4 Comparability

Comparability is the extent to which data from one study can be compared directly to either past 

data from the current project or data from another study. Using standardized sampling and 

analytical methods, units of reporting, and site selection procedures help ensure comparability. 

Standard field sampling and typical laboratory protocols were used during the SI and are 

considered comparable to ongoing investigations.

4.6.5 Completeness

Completeness is a measure of the amount of valid data obtained from a measurement system 

compared to the amount of data expected under normal conditions. The laboratory provided data 

meeting system QC acceptance criteria for all samples tested. Project completeness was 

determined by evaluating the planned versus actual quantities of data. Percent completeness per 

parameter is as follows:

• PFAS in groundwater by USEPA Method 537 Modified at 100%

• PFAS in soil by USEPA Method 537 Modified at 100%

• PFAS in surface water by USEPA Method 537 Modified at 100%

• PFAS in sediment by USEPA Method 537 Modified at 100%
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 4-6

• pH in soil by USEPA Method 9045D at 100%

• Total Organic Carbon (TOC) by USEPA Method 9060 at 100%

4.6.6 Sensitivity

Sensitivity is the capability of a test method or instrument to discriminate between measurement 

responses representing different levels (e.g., concentrations) of a variable of interest. Examples 

of QC measures for determining sensitivity include laboratory fortified blanks, a method detection 

limit (MDL) study, and calibration standards at the limit of quantitation (LOQ). In order to meet the 

needs of the data users, project data must meet the measurement performance criteria for 

sensitivity and project LOQs specified in the QAPP Addendum (AECOM, 2018e). The laboratory 

provided the requested MDL studies and provided applicable calibration standards at the LOQ. In 

order to achieve the DQOs for sensitivity outlined in the QAPP Addendum (AECOM, 2018e), the 

laboratory reported all field sample results at the lowest possible dilution. Additionally, any 

analytes detected below the LOQ and above the DL were reported and qualified “J” as estimated 

values by the laboratory.
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 5-1

5.0 Site Inspection Activities

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

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

implemented in accordance with the following approved documents: 

• Final Preliminary Assessment Report, Army Aviation Support Facility, St. Cloud,

Minnesota dated April 2019 (AECOM, 2019a);

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

dated October 2019 (AECOM, 2018a);

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

Army Aviation Support Facility, St. Cloud, Minnesota dated July 2019 (AECOM, 2019b);

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

• Final Site Safety and Health Plan, Army Aviation Support Facility, St. Cloud, Minnesota

dated October 2019 (AECOM, 2019c).

The SI field activities were conducted from 15-17 October 2019 and 11-12 May 2020 and

consisted of direct push boring and soil sample collection, temporary monitoring well installation, 

grab groundwater sample collection, and surface water and sediment sample collection. Field 

activities were conducted in accordance with the QAPP Addendum (AECOM, 2019b), except as 

noted in Section 5.7. 

The following samples were collected during the SI and analyzed for PFAS via LC/MS/MS 

compliant with QSM 5.1 Table B-15 to fulfill the project DQOs:

• Eighteen (18) soil samples from six locations;

• Six grab groundwater samples from six temporary well locations;

• Five sediment samples; and

• Four surface water samples, which were co-located with sediment 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, which is provided in Appendix B1, was completed throughout the 

SI field activities. Sampling Forms are provided in Appendix B2, Nonconformance and Corrective 

Action Reports are provided in Appendix B3, and Investigation-Derived Waste (IDW) Polygons 

are provided as Appendix B4. Additionally, a photographic log of field activities is provided in 

Appendix C. 

5.1 Pre-Investigation Activities

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

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

water. Details of these activities are presented below.

5.1.1 Technical Project Planning

The USACE TPP Process, (Engineers Manual [EM] 200-1-2 (USACE, 2016) defines four phases 

to project planning: 1) defining the project phase; 2) determining data needs; 3) developing data 

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

stakeholder involvement in the SI, beginning with defining overall project objectives, including 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 5-2

quantitative and qualitative DQOs, and formulating a sampling approach to address the AOIs 

identified in the PA. 

A combined TPP Meeting 1 and 2 was held on 2 October 2019, 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 ARNG, MNARNG, USACE, St. Cloud AASF #2 personnel, 

Minnesota Department of Health (MDH), the Minnesota Pollution Control Agency, representatives

familiar with the facility, the regulations, and the community. 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, 2019b). 

A TPP Meeting 3 was held on 17 August 2021 after the field event 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

AECOM’s drilling subcontractor, Dakota Technical Services, contacted “Gopher State” one-call 

utility clearance to notify them of intrusive work. Additionally, the first 5 feet of each boring were 

advanced using hand auguring methods to verify utility clearance in shallow subsurface where 

utilities would typically be encountered. 

5.1.3 Source Water and PFAS Sampling Equipment Acceptability

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

PFAS-free prior to the start of field activities. The results of the potable well sample are provided 

in Appendix F. A discussion of the results is presented in Section 4.6.3. 

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

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

environment was provided in the Standard Operating Procedures (SOPs) appendix to the

Programmatic UFP-QAPP (PQAPP) (AECOM, 2018a). Prior to the start of field work each day, a

PFAS 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 direct-push technology (DPT) in accordance with Standard 

Operating Procedure 3-17 Direct Push Sampling Techniques. A GeoProbe® 6610DT dual-tube 

sampling system was used to collect continuous soil cores to the target depth. Three discrete soil 

samples were collected for chemical analysis from each soil boring. A hand auger was used to 

collect samples from 0 to 2 feet bgs to be compliant with utility clearance procedures. One 

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

soil sample at the mid-point between the surface and the groundwater table were collected at 

each boring using DPT. 

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

boring locations were selected based on the AOI information as agreed on through TPP and 

QAPP Addendum review. 

The soil cores were continuously logged for lithological descriptions by a field geologist using the 

Unified Soil Classification System (USCS). A photoionization detector (PID) was used to screen 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 5-3

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 non-treated 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. 

Each sample was collected into laboratory-supplied PFAS-free high-density polyethylene (HDPE) 

bottles and labeled using a PFAS-free marker or pen. Samples were packaged on ice and 

transported via Federal Express (FedEx) under standard chain of custody (CoC) procedures to 

the laboratory and analyzed for PFAS by LC/MS/MS Compliant with QSM 5.1 Table B-15, TOC 

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

Addendum (AECOM, 2019b). 

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

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

same parameters as the accompanying samples. In instances when non-dedicated sampling 

equipment was used, such as a hand auger for the shallow soil samples, ERBs 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 4 degrees Celsius (°C) 

during shipment.

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

accordance with the QAPP Addendum (AECOM, 2019b) using bentonite chips at completion of 

sampling activities. Borings were installed in grass areas to avoid disturbing concrete or asphalt 

surfaces. 

5.3 Temporary Well Installation and Groundwater Grab Sampling 

Temporary wells were installed using a GeoProbe® 6610DT dual-tube sampling system. 

Temporary wells were installed at all six boring locations. Once the borehole was advanced to the 

desired depth, a temporary well was constructed of 5- or 10-feet sections of 1-inch Schedule 40 

poly-vinyl chloride (PVC) screen with sufficient casing to reach ground surface. New PVC pipe 

and screen were used at each location to avoid cross contamination between locations. The 

screen intervals for the temporary wells are provided on Table 5-2. 

The temporary wells were allowed to recharge for a minimum of 24 hours after installation before 

collection of groundwater samples. After the recharge period, groundwater samples were 

collected using a peristaltic pump with PFAS-free HDPE tubing. Each sample was collected into 

laboratory-supplied PFAS-free HDPE bottles and labeled using a PFAS-free marker or pen. The 

temporary wells were purged at a rate determined in the field to reduce turbidity and draw down 

prior to sampling. Water quality parameters (e.g., temperature, specific conductance, pH, 

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

quality meter and recorded on the field sampling form (Appendix B2) after each grab sample was 

collected. 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 for PFAS by LC/MS/MS Compliant with 

QSM 5.1 Table B-15 in accordance with the QAPP Addendum (AECOM, 2019b).

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

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

same parameters as the accompanying samples. One FRB was collected in accordance with the 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 5-4

PQAPP (AECOM, 2018a). A temperature blank was placed in each cooler to ensure that samples 

were preserved at or below 4°C during shipment.

Temporary wells were abandoned in accordance with the QAPP Addendum (AECOM, 2019b) by 

removing the PVC and backfilling the hole with bentonite chips. Temporary wells were installed in 

grass areas to avoid disturbing concrete or asphalt. 

5.4 Surface Water and Sediment Sampling

Sediment samples were co-located with surface water, and sediment samples were collected 

from stormwater drains on AASF #2 boundary that discharge to the Elk River. The Elk River runs 

parallel to the Mississippi River before converging at the city of Elk River, Minnesota. 

Surface water samples were collected from a single point in the waterbody by dipping the 

laboratory-supplied bottle into the water, approximately two-thirds up from the bottom of the water 

body. For the co-located surface water and sediment samples, the surface water sample was 

collected before the co-located sediment sample. Sampling was performed deliberately and 

methodically to minimize disturbance of bottom sediments and as quickly as possible to ensure a 

representative sample was collected. Additionally, a subsample of each surface water sample 

was collected in a separate container, and a shaker test was completed to identify if there were 

any foaming. No foaming was noted on any of the surface water samples.

After collection of the surface water sample, a sediment coring device (hand auger) was used to 

collect the sediment sample from the first 1 foot of sediment. The sediment was transferred to a 

Ziploc bag, where the sample was homogenized, and stones in excess of 1 centimeter were 

removed. The surface water and sediment sample locations are shown on Figure 5-1, and sample 

depths are provided in Table 5-1. 

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 for analysis of PFAS (USEPA Method 537 Compliant 

with QSM 5.1 Table B-15). Sediment samples were also analyzed for TOC (USEPA Method 

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

2019b). 

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

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

same parameters as the accompanying samples. In instances when non-dedicated sampling 

equipment was used, ERB samples 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 4°C during shipment.

5.5 Investigation-Derived Waste

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

generated during the SI is considered non-hazardous waste and was managed in accordance 

with the QAPP Addendum (AECOM, 2019b) and with the Army Guidance for Addressing Releases 

of PFAS, Q18 (DA, 2018). 

Soil IDW (i.e., soil cuttings) generated during the SI activities were left in place at the point of the 

source. The soil cuttings were distributed on the ground surface on the downgradient side of the 

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

soil samples collected from that source location. 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 5-5

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

decontamination fluids) was discharged directly to the ground surface slightly downgradient of the 

source. The liquid IDW was not sampled and assumes the PFAS 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 B5. 

Other solids such as spent personal protective equipment (PPE), plastic sheeting, tubing, rope, 

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

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

5.6 Laboratory Analytical Methods

Samples were analyzed for PFAS by LC/MS/MS compliant with QSM 5.1 Table B-15 at Pace Gulf 

Coast in Baton Rouge, Louisiana, a DoD ELAP and NELAP-certified laboratory. The 18 PFAS 

compounds analyzed as part of the ARNG SI program include the following: 

• 6:2 fluorotelomer sulfonic acid (6:2 

FTS)

• 8:2 fluorotelomer sulfonic acid (8:2 

FTS)

• N-ethyl 

perfluorooctanesulfonamidoacetic acid 

(NEtFOSAA) 

• N-methyl 

perfluorooctanesulfonamidoacetic acid 

(NMeFOSAA) 

• Perfluorobutyrate (PFBA) 

• Perfluorobutanesulfonic acid (PFBS)

• Perfluorodecanoic acid (PFDA)

• Perfluorododecanoic acid (PFDoA) 

• Perfluoroheptanoic acid (PFHpA)

• Perfluorohexanoic acid (PFHxA)

• Perfluorohexanesulfonic acid (PFHxS)

• Perfluorononanoic acid (PFNA)

• Perfluorooctanoic acid (PFOA)

• Perfluorooctanesulfonic acid (PFOS)

• Perfluoropentanoic acid (PFPeA)

• Perfluorotetradecanoic acid (PFTeDA)

• Perfluorotridecanoic acid (PFTrDA)

• Perfluoroundecanoic acid (PFUdA)

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

USEPA Method 9045D. 

5.7 Deviations from QAPP Addendum

Deviations from the QAPP Addendum occurred based on field conditions and discussion between 

AECOM, ARNG, MNARNG, and USACE. One deviation from the QAPP Addendum is noted 

below and is documented in the Nonconformance and Corrective Action Report (Appendix B.3): 

• The QAPP Addendum stated that five surface water and five sediment samples were to 

be collected soil samples; however, surface water at SD/SW05 was not present at the time 

of the investigation. Although, surface water was not present, a sediment sample was 

collected and analyzed from SD/SW05. 

• The QAPP stated all samples were to be collected within the facility boundary. Soil and 

groundwater samples from AOI1-SB04 and surface water and sediment samples 

SW/SD03 were not collected in the proper locations. An additional mobilization to the Site 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 5-6

was conducted to collect the above samples from the correct locations. Information 

presented in this report was collected in accordance with the approved UFP QAPP. 
Table 5-1

Samples by Medium

Site Inspection Report, St. Cloud AASF #2

Sample Identification

Sample

Collection

Date

Sample Depth

(feet bgs)

PFAS(USEPA Method 537 Modified)TOC(USEPA Method 9060A)pH(USEPA Method 9045D)

Comments

AOI 1-SB01 10/16/2019 0.5 - 1 x x x

AOI 1-SB01 DUP 10/16/2019 0.5 - 1 x x x Field Duplicate

AOI 1-SB01 MS 10/16/2019 0.5 - 1 x MS/MSD

AOI 1-SB01 MSD 10/16/2019 0.5 - 1 x MS/MSD

AOI 1-SB01 10/16/2019 2.5 - 5 x x x

AOI 1-SB01 10/16/2019 5 - 7.5 x x x

AOI 1-SB02 10/15/2019 0.5 - 1 x x x

AOI 1-SB02 DUP 10/15/2019 0.5 - 1 x x x Field Duplicate

AOI 1-SB02 10/15/2019 5 - 10 x x x

AOI 1-SB02 10/15/2019 12.5 - 15 x x x

AOI 1-SB03 10/15/2019 0.5 - 1 x x x

AOI 1-SB03 10/15/2019 5 - 7.5 x x x

AOI 1-SB03 10/15/2019 7.5 - 10 x x x

AOI 1-SB04 5/11/2020 0.5 - 1.5 x

AOI 1-SB04 DUP 5/11/2020 0.5 - 1.5 x Field Duplicate

AOI 1-SB04 MS 5/11/2020 0.5 - 1.5 x MS/MSD

AOI 1-SB04 MSD 5/11/2020 0.5 - 1.5 x MS/MSD

AOI 1-SB04 5/11/2020 5 - 7.5 x

AOI 1-SB04 5/11/2020 10 - 12.5 x x x

AOI 1-SB05 10/15/2019 0.5 - 1 x x x

AOI 1-SB05 10/15/2019 5 - 7.5 x x x

AOI 1-SB05 10/15/2019 10 - 12.5 x x x

AOI 1-SB06 10/15/2019 0.5 - 1 x x x

AOI 1-SB06 10/15/2019 2.5 - 5 x x x

AOI 1-SB06 10/15/2019 5 - 7.5 x x x

SD01 10/15/2019 0 - 1 x x x

SD02 10/15/2019 0 - 1 x x x

SD03 5/12/2020 0 - 1 x x x

SD04 10/15/2019 0 - 1 x x x

SD05 10/16/2019 0 - 1 x x x

AOI 1-SB01 10/17/2019 10 - 15 x

AOI 1-SB02 10/16/2019 10 - 15 x

Sediment Samples

Soil Samples

Groundwater Samples

AECOM 5-7
Table 5-1

Samples by Medium

Site Inspection Report, St. Cloud AASF #2

Sample Identification

Sample

Collection

Date

Sample Depth

(feet bgs)

PFAS(USEPA Method 537 Modified)TOC(USEPA Method 9060A)pH(USEPA Method 9045D)

Comments

AOI 1-SB03 10/16/2019 10 - 15 x

AOI 1-SB03 DUP 10/16/2019 10 - 15 x Field Duplicate

AOI 1-SB04 5/12/2020 10 - 15 x MS/MSD

AOI 1-SB04 DUP 5/12/2020 10 - 15 x Field Duplicate

AOI 1-SB05 10/17/2019 10 - 15 x

AOI 1-SB06 10/17/2019 10 - 15 x

SW01 10/15/2019 0 - 1 x

SW02 10/15/2019 0 - 1 x

SW03 5/12/2020 0 - 1 x

SW04 10/15/2019 0 - 1 x

EB-101719-GW 10/17/2019 --- x Equipment Blank

ERB-01 5/12/2020 --- x Equipment Blank

FRB-01 5/12/2020 --- x Field Blank

Notes:

ft = feet

MS/MSD = matrix spike/ matrix spike duplicate

PFAS = per- and polyfluoroalkyl substances

pH = potential for hydrogen

TOC =total organic carbon

USEPA = United States Environmental Protection Agency

Blank Samples

Surface Water Samples

AECOM 5-8
Table 5-2

Soil Boring, Temporary Well, and Gauging Data

Site Inspection Report, St. Cloud AASF #2

Area of

Interest Soil Boring ID Soil Boring Depth(ft bgs)

Temporary

Well Screen

Interval

(ft bgs)

Depth to

Water

(ft btoc)

AOI 1-SB01 15 10 - 15 3.45

AOI 1-SB02 22.5 10 - 20 11.10

AOI 1-SB03 15 10 - 15 4.45

AOI 1-SB04 25 15 - 25 13.22

AOI 1-SB05 20 10 - 15 11.05

AOI 1-SB06 20 10 - 15 4.20

Notes:

btoc = below top of casing

bgs = below ground surface

ft = feet

AOI 1

AECOM 5-9
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 5-10

THIS PAGE INTENTIONALLY BLANK 
"J

!?

"J

"J

!?

!?

"J "J

!?

!?

!?

Northeastern

Detention Pond

Southwestern

Detention Pond

AOI 1

SD/SW01

AOI1-SB03

SD/SW02

SD/SW03

AOI1-SB04

AOI1-SB05

SD/SW04

SD/SW05

AOI1-SB06

AOI1-SB01

AOI1-SB02

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

SI

5/27/2021

5/27/2021

NOTES Site Inspection for PFAS at St. Cloud AASF #2, MN

1:4,800

5/27/2021 ­ Figure 5-1

PM CM 5/27/2021

12420 Milestone Center Drive

Germantown, MD 20876

Site Inspection 

Sampling Locations

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

Geographics, CNES/Airbus DS, USDA, USGS,

Q:\Projects\ENV\GEARS\GEO\ARNG PFAS\900-CAD-GIS\920-GIS or Graphics\MXD\MN\StCloud_SI_Figures\

Legend

!? 30 ft DPT Boring/Temp

Well Location

"J Surfacewater/Sedmient

Sample Location

Area of Interest

Facility Boundary

Water Body

Canal/Ditch

0 180 360 720

Feet

AECOM 5-11
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 5-12

THIS PAGE INTENTIONALLY BLANK
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 6-1

6.0 Site Inspection Results 

This section presents the analytical results of the SI for AOI 1. The SLs used in this evaluation 

are presented in Section 6.1. A discussion of the results for AOI 1 is provided in Section 6.3. 

Table 6-2 through Table 6-4 present PFAS results for samples with detections in soil, 

groundwater, and surface water; only constituents detected in one or more samples are included. 

No constituents were detected in sediment; therefore, a table of detections is not presented in 

this section. 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 15 October 

2019 (Assistant Secretary of Defense, 2019). The ARNG program under which this SI was 

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

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

CERCLA. The SLs apply to three compounds, PFOA, PFOS, and PFBS, for both soil and 

groundwater, as presented in Table 6-1. 

All other results presented in this report are considered informational in nature and serve as an 

indication as to whether soil, groundwater, sediment, and surface water contain or do not contain 

PFAS within the boundaries of the facility. 

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

Analyte

Residential

(Soil)

(μg/kg)a,b

0-2 feet bgs

Industrial/ Commercial 

Composite Worker

(Soil)

(μg/kg)a,b

2-15 feet bgs

Tap Water

(Groundwater) 

(ng/L)a,b

PFOA 130 1,600 40

PFOS 130 1,600 40

PFBS 130,000 1,600,000 40,000

Notes:

a.) Assistant Secretary of Defense, 2019. Risk Based Screening Levels Calculated for PFOS, PFOA, PFBS in 

Groundwater and Soil using United States Environmental Protection Agency’s (USEPA’s) Regional Screening 

Level Calculator. HQ=0.1. 15 October 2019.

6.2 Soil Physicochemical Analyses

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

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

of the TOC and pH sampling. 

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

appropriate, to assess fate and transport of PFAS contaminants. According to the Interstate 

Technology Regulatory Council (ITRC), several important PFAS-partitioning mechanisms include 

hydrophobic and lipophobic effects, electrostatic interactions, and interfacial behaviors. At 

relevant environmental pH values, certain PFAS are present as organic anions and are therefore 

relatively mobile in groundwater (Xiao et al., 2015) but tend to associate with the organic carbon 

fraction that may be present in soil or sediment (Higgins and Luthy 2006; Guelfo and Higgins, 

2013). When sufficient organic carbon is present, organic carbon normalized distribution 

coefficients (Koc values) can help in evaluating transport potential, though other geochemical 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 6-2

factors (for example, pH and presence of polyvalent cations) may also affect PFAS sorption to 

solid phases (ITRC, 2018).

6.3 AOI 1 – St. Cloud AASF #2

This section presents the analytical results for soil, groundwater, surface water, and sediment for 

AOI 1. The detected compounds are summarized in Table 6-2 through Table 6-4 and on Figures 

6-1 through Figure 6-5. 

6.3.1 Soil Analytical Results

Soil samples were collected within the source area and perimeter of AOI 1 from the surface, 

shallow subsurface, and capillary fringe. PFOA, PFOS, and PFBS were not detected in the soil 

samples. Figure 6-1 presents analytical results in soil for PFOS, and Figure 6-2 presents the 

analytical results in soil for PFOA. The detected compounds from the soil sampling are 

summarized in Table 6-2.

6.3.2 Groundwater Analytical Results

PFOA and PFOS were detected in four of the eight groundwater samples collected from 

temporary wells. PFBS was not detected in groundwater. PFOA was detected in AOI1-SB03, 

AOI1-SB03 duplicate sample (DUP #1), and AOI1-SB06 at concentrations of 2.74 J ng/L, 1.80 J 

ng/L, and 1.76 J ng/L, respectively. 

PFOS was detected in one of the eight groundwater samples collected from temporary wells. 

PFOS was detected at a concentration of 1.85 J ng/L in the duplicate sample collected from AOI1-

SB04 (AOI01-04-GW-D). 

PFBS was not detected in groundwater and the detected PFOA and PFOS concentrations of did 

not exceed the SLs. Figure 6-3 presents analytical results for PFAS in groundwater. The detected 

compounds from groundwater sampling are summarized in Table 6-3. 

6.3.3 Sediment Analytical Results

Sediment samples were collected from stormwater drains that flow east into the Elk River. The 

Elk River runs parallel to the Mississippi River before converging at the city of Elk River. PFOA, 

PFOS, and PFBS were not detected in sediment samples at the facility. 

6.3.4 Surface Water Analytical Results

Surface water samples were collected from stormwater drains that flow east into the Elk River, 

downgradient of AOI 1. PFOA, PFOS, and PFBS were detected in the surface water sample 

collected at SW01 at concentrations of 2.58 J ng/L, 3.67 J ng/L, and 1.51 J ng/L, respectively. 

PFOS was detected at a concentration of 4.34 J ng/L in the surface water sample collected at 

AOI01-03-SW. 

Figure 6-5 presents analytical results for surface water for PFOS and PFOA. Table 6-4 

summarizes the detected compounds in surface water and presents the ranges of detections for 

PFOS, PFOA, and PFBS in surface water.

6.3.5 Conclusions

Based on the results of the SI, PFOA and PFOS were detected in groundwater at concentrations 

below the SLs at AOI 1. PFBS was not detected in groundwater. PFOA, PFOS, and PFBS were
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 6-3

detected in surface water at AOI 1 but were not detected in soil or sediment. There are no 

established SLs for sediment and surface water; therefore, these results are presented for 

informational purposes only.
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 6-4

THIS PAGE INTENTIONALLY BLANK
Table 6-2

PFAS Detections in Shallow Subsurface Soil

Site Inspection Report, St. Cloud AASF #2

Analyte OSD Screening

Level a

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

PFBA - ND ND ND ND ND ND 0.200 J ND ND ND

References Chemical Abbreviations

PFBA perfluorobutanoic acid

Acronyms and Abbreviations

AOI Area of Interest

D/DUP Duplicate

ft feet

HQ Hazard quotient

Interpreted Qualifiers LCMSMS Liquid Chromatography Mass Spectrometry

J = Estimated concentration LOD Limit of Detection

ND Analyte not detected above the LOD

OSD Office of the Secretary of Defense

QSM Quality Systems Manual

Qual Interpreted Qualifier

SB Soil boring

USEPA United States Environmental Protection Agency

ug/Kg micrograms per Kilogram

- Not applicable

Area of Interest

Sample ID

Sample Date

Depth

AOI1-SB01 (2.5-5)

10/16/2019

2.5 - 5 ft 5 - 7.5 ft

AOI1

AOI1-SB02 (12.5-15)

10/15/2019

12.5 - 15 ft

AOI1-SB03 (5-7.5)

10/15/2019

5 - 7.5 ft

AOI1-SB01 (5-7.5)

10/16/2019

5 - 7.5 ft

AOI1-SB02 (5-10)

10/15/2019

5 - 10 ft

a. Assistant Secretary of Defense, 2019. Risk Based Screening Levels Calculated for PFOS, PFOA, PFBS in Groundwater or Soil using USEPA’s Regional

Screening Level Calculator. HQ=0.1. 15 October 2019. Soil screening levels based on industrial/commercial composite worker scenario for incidental

ingestion of contaminated soil.

AOI1-SB05 (10-12.5)

10/15/2019

10 - 12.5 ft

Soil, PFAS by LCMSMS Compliant with QSM 5.1 Table B-15 (ug/Kg)

AOI01-04-SB-10-12.5

05/11/2020

10 - 12.5 ft

AOI1-SB05 (5-7.5)

10/15/2019

5 - 7.5 ft

AOI1-SB03 (7.5-10)

10/15/2019

7.5 - 10 ft

AOI01-04-SB-5-7.5

05/11/2020

AECOM 6-5
Table 6-3

PFAS Detections in Groundwater

Site Inspection Report, St. Cloud AASF #2

Analyte OSD Screening

Level a

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

Water, PFAS via PFAS by LCMSMS Compliant with QSM 5.1 Table B-15 (ng/L)

6:2 FTS - ND ND ND ND ND 2.19 J ND ND

PFHpA - ND ND ND ND ND ND ND 1.85 J

PFHxA - ND ND ND 1.73 J ND ND ND 3.19 J

PFOA 40 ND ND 2.74 J 1.80 J ND ND ND 1.76 J

PFOS 40 ND ND ND ND ND 1.85 J ND ND

PFPeA - ND ND ND ND ND ND ND 2.79 J

PFTeDA - ND ND ND ND ND ND ND 2.56 J+

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

6:2 FTS 6:2 fluorotelomer sulfonate

PFHpA perfluoroheptanoic acid

PFHxA perfluorohexanoic acid

References PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

PFPeA perfluoropentanoic acid

PFTeDA perfluorotetradecanoic acid

Acronyms and Abbreviations

AOI Area of Interest

D/DUP Duplicate

Interpreted Qualifiers ft feet

J = Estimated concentration HQ Hazard quotient

J+ = Estimated concentration, biased high LC/MS/MS Liquid Chromatography Mass Spectrometry

LOD Limit of Detection

ND Analyte not detected above the LOD

OSD Office of the Secretary of Defense

QSM Quality Systems Manual

Qual Interpreted Qualifier

SB Soil boring

USEPA United States Environmental Protection Agency

ug/Kg micrograms per Kilogram

- Not applicable

a. Assistant Secretary of Defense, 2019. Risk Based Screening Levels Calculated for PFOS, PFOA, PFBS in Groundwater or

Soil using USEPA’s Regional Screening Level Calculator. HQ=0.1. 15 October 2019. Groundwater screening levels based on

residential scenario for direct ingestion of groundwater.

AOI1-SB05 AOI1-SB06

10/17/2019 10/17/2019

Area of Interest

Sample ID

Sample Date

AOI1-SB01

10/17/2019

AOI1

AOI01-04-GW

05/12/2020

AOI01-04-GW-D

05/12/2020

DUP #1-20191016

10/16/2019

AOI1-SB03

10/16/2019

AOI1-SB02

10/16/2019

AECOM 6-6
Table 6-4

PFAS Detections in Surface Water

Site Inspection Report, St. Cloud AASF #2

Area of Interest

Sample ID

Sample Date

Analyte Result Qual Result Qual Result Qual Result Qual

Water, PFAS via PFAS by LCMSMS Compliant with QSM 5.1 Table B-15 (ng/L)

6:2 FTS 111 ND 44.3 ND

PFBA ND ND 11.9 ND

PFBS 1.51 J ND ND ND

PFHpA 8.11 J ND 5.10 J ND

PFHxA 36.9 ND 18.9 ND

PFHxS 3.75 J ND 2.92 J ND

PFOA 2.58 J ND ND ND

PFOS 3.67 J ND 4.34 J ND

PFPeA 67.3 ND 37.3 ND

Interpreted Qualifiers Chemical Abbreviations

J = Estimated concentration 6:2 FTS 6:2 fluorotelomer sulfonate

PFBA perfluorobutanoic acid

PFBS perfluorobutanesulfonic acid

PFHpA perfluoroheptanoic acid

PFHxA perfluorohexanoic acid

PFHxS perfluorohexanesulfonic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

PFPeA perfluoropentanoic acid

Acronyms and Abbreviations

AOI Area of Interest

LC/MS/MS Liquid Chromatography Mass Spectrometry

LOD Limit of Detection

ND Analyte not detected above the LOD

QSM Quality Systems Manual

Qual Interpreted Qualifier

SW Surface water

ng/L nanogram per liter

SW01

10/15/2019

AOI1

SW04

10/15/2019

SW02

10/15/2019

AOI01-03-SW

05/12/2020

AECOM 6-7
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 6-8

THIS PAGE INTENTIONALLY BLANK
Northeastern

Detention Pond

Southwestern

Detention Pond

AOI 1

AOI1-SB03

AOI1-SB04

AOI1-SB05

AOI1-SB06

AOI1-SB01

Northeastern

Detention Pond

Southwestern

Detention Pond

AOI 1

AOI1-SB03

AOI1-SB04

AOI1-SB05

AOI1-SB06

AOI1-SB01

AOI1-SB02

Q:\Projects\ENV\GEARS\GEO\ARNG PFAS\900-CAD-GIS\920-GIS or Graphics\MXD\MN\StCloud_SI_Figures\

Northeastern

Detention Pond

Southwestern

Detention Pond

AOI 1

AOI1-SB03

AOI1-SB04

AOI1-SB05

AOI1-SB06

AOI1-SB01

AOI1-SB02

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-1

PFOS Detections in Soil

5/27/2021

5/27/2021

MS 5/27/2021

JP

CM

GIS BY

CHK BY

PM

5/27/2021

1:5,040

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection for PFAS at St. Cloud AASF #2, MN

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

Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN,

0 210 420 840

Feet

Shallow

Intermediate

Deep

Area of Interest

Facility Boundary

PFOS Results (μg/Kg)

ND

>ND - 10

>10 - 130

>130 - 1,600

>1,600

AECOM 6-9
Northeastern

Detention Pond

Southwestern

Detention Pond

AOI 1

AOI1-SB03

AOI1-SB04

AOI1-SB05

AOI1-SB06

AOI1-SB01

Northeastern

Detention Pond

Southwestern

Detention Pond

AOI 1

AOI1-SB03

AOI1-SB04

AOI1-SB05

AOI1-SB06

AOI1-SB01

AOI1-SB02

C:\Users\stankevichm\OneDrive - AECOM Directory\ARNG_PFAS_GIS_60552172\MXDs\MN\StCloud_Figures\StCloud_SI_Figures\SI_Report\Fig_6-2_StCloud_PFOA_Soil_Results.mxd

Northeastern

Detention Pond

Southwestern

Detention Pond

AOI 1

AOI1-SB03

AOI1-SB04

AOI1-SB05

AOI1-SB06

AOI1-SB01

AOI1-SB02

AOI1-SB02

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-2

PFOA Detections in Soil

5/27/2021

5/27/2021

MS 5/27/2021

JP

CM

GIS BY

CHK BY

PM

5/27/2021

1:5,040

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection for PFAS at St. Cloud AASF #2, MN

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

Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN,

0 210 420 840

Feet

Shallow

Intermediate

Deep

Area of Interest

Facility Boundary

PFOA Results (μg/Kg)

ND

>ND - 10

>10 - 130

>130 - 1,600

>1,600

AECOM 6-10
Northeastern

Detention Pond

Southwestern

Detention Pond

AOI 1

AOI1-SB03

AOI1-SB04

AOI1-SB05

AOI1-SB06

AOI1-SB01

AOI1-SB02

Northeastern

Detention Pond

Southwestern

Detention Pond

AOI 1

AOI1-SB03

AOI1-SB04

AOI1-SB05

AOI1-SB06

AOI1-SB01

AOI1-SB02

Q:\Projects\ENV\GEARS\GEO\ARNG PFAS\900-CAD-GIS\920-GIS or Graphics\MXD\MN\StCloud_SI_Figures\

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-3

PFOA & PFOS Detections 

in Groundwater

5/27/2021

5/27/2021

MS 5/27/2021

JP

CM

GIS BY

CHK BY

PM

5/27/2021

1:4,200

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection for PFAS at St. Cloud AASF #2, MN

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

Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN,

0 175 350 700

Feet

PFOA

PFOS

Area of Interest

Facility Boundary

PFOA Results (ng/L)

ND

>ND - 10

>10 - 40

>40 - 70

>70 - 400

>400

PFOS Results (ng/L)

ND

>ND - 10

>10 - 40

>40 - 70

>70 - 400

>400

AECOM 6-11
Northeastern

Detention Pond

Southwestern

Detention Pond

AOI 1

SD/SW01

SD/SW02

SD/SW03

SD/SW04

Northeastern

Detention Pond

Southwestern

Detention Pond

AOI 1

SD/SW01

SD/SW02

SD/SW03

SD/SW04

Q:\Projects\ENV\GEARS\GEO\ARNG PFAS\900-CAD-GIS\920-GIS or Graphics\MXD\MN\StCloud_SI_Figures\

Figure 6-4

PFOA and PFOS Detections in Surface Water

12420 Milestone Center Drive ­ Germantown, MD 20876

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection for PFAS at St. Cloud AASF #2, MN

5/27/2021

5/27/2021

5/27/2021

MS

JP

CM

GIS BY

CHK BY

PM

Base Map: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS,

USDA, USGS, AeroGRID, IGN, and the GIS User Community

5/27/2021

1:4,560

0 190 380 760

Feet

PFOA PFOS

Area of Interest

Facility Boundary

PFOA Results (ng/L)

ND

>ND - 10

>10 - 100

>100 - 1,000

>1,000

PFOS Results (ng/L)

ND

>ND - 10

>10 - 100

>100 - 1,000

>1,000

AECOM 6-12
Northeastern

Detention Pond

Southwestern

Detention Pond

AOI 1

SD/SW01

SD/SW02

SD/SW03

SD/SW04 SD/SW05

Northeastern

Detention Pond

Southwestern

Detention Pond

AOI 1

SD/SW01

SD/SW02

SD/SW03

SD/SW04 SD/SW05

Q:\Projects\ENV\GEARS\GEO\ARNG PFAS\900-CAD-GIS\920-GIS or Graphics\MXD\MN\StCloud_SI_Figures\

Figure 6-5

PFOA and PFOS Detections in Sediment

12420 Milestone Center Drive ­ Germantown, MD 20876

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection for PFAS at St. Cloud AASF #2, MN

5/27/2021

5/27/2021

5/27/2021

MS

JP

CM

GIS BY

CHK BY

PM

Base Map: Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS,

USDA, USGS, AeroGRID, IGN, and the GIS User Community

5/27/2021

1:4,560

0 190 380 760

Feet

PFOA PFOS

Area of Interest

Facility Boundary

PFOA Results (μg/Kg)

ND

>ND - 10

>10 - 100

>100 - 1,000

>1,000

PFOS Results (μg/Kg)

ND

>ND - 10

>10 - 100

>100 - 1,000

>1,000

AECOM 6-13
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 6-14

THIS PAGE INTENTIONALLY BLANK 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 7-1

7.0 Exposure Pathways

The CSM for AOI 1, revised based on the SI findings, is presented on Figure 7-1. A CSM presents 

the current understanding of the facility 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 

PFOA, PFOS, or PFBS 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 PFOA, PFOS, 

or PFBS above the SLs. Areas with an identified potentially complete pathway may warrant further 

investigation.

In general, the potential PFAS exposure pathways 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 PFAS toxicological study. The receptors evaluated are consistent with 

those listed in USEPA guidance for risk screening (USEPA, 2001). Receptors at the facility include 

facility workers, construction workers, trespassers, and nearby off-facility residents. 

7.1 Soil Exposure Pathway

The SI results for PFOA, PFOS, and PFBS in soil were used to determine whether a potentially 

complete pathway exists between the source and potential receptors at AOI 1 based on the 

aforementioned criteria. 

7.1.1 AOI 1 – St. Cloud AASF #2

Releases of HEF occurred from the HEF fire suppression system at AASF #2 in 2009, 2011, and 

2013. After the releases in 2009 and 2011, HEF was washed to the sanitary sewer and is, 

therefore, not suspected to have impacted AOI 1. However, after the release in June 2013, HEF

was washed out of both sides of the hangar and plowed into the northeast and southwest 

detention ponds by the MNARNG. In addition, rotary-winged aircraft were washed on the 

northeast side of the hangar following the release, and the wash water could have dissipated in 

the northeast detention pond. Photographs provided by the MNARNG show HEF on the ground 

surface throughout the entire facility boundary and on the AASF #2 building following the June 

2013 release.

PFOA, PFOS, and PFBS were not detected in soil at the facility. Based on the results of the SI, 

the exposure pathways via inhalation of dust and ingestion of soil are considered incomplete. The

CSM is presented in Figure 7-1. 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 7-2

7.2 Groundwater Exposure Pathway

The SI results for PFOA, PFOS, and PFBS in groundwater were used to determine whether a 

potentially complete pathway exists between the source and potential receptors at AOI 1 based 

on the aforementioned criteria. 

7.2.1 AOI 1 – St. Cloud AASF #2 

PFOA and PFOS were detected in groundwater from temporary monitoring wells at low levels in

the source area and at the facility boundary; however, the detections did not exceed the SLs. 

PFBS was not detected in groundwater at the facility. Drinking water for AASF #2 is supplied by 

the City of St. Cloud, which uses the Mississippi River as its drinking water source (City of St. 

Cloud, 2011). Therefore, the ingestion exposure pathway is considered incomplete for facility 

workers, and trespassers. Domestic wells exist within 4 miles of the facility, and private, residential 

wells were observed in the area during the visual site inspection. Therefore, the ingestion 

exposure pathway is considered potentially complete for downgradient, off-facility residents. 

Additionally, the ingestion exposure pathway for future construction workers is considered 

potentially complete due to the detection of PFOA and PFOS. No current construction is occurring 

at AOI 1. The CSM is presented on Figure 7-1. 

7.3 Surface Water and Sediment Exposure Pathways 

The SI results for PFOA, PFOS, and PFBS in surface water and sediment were used to determine 

whether a potentially complete pathway exists between the source and potential receptors at 

AOI 1 based on the aforementioned criteria.

7.3.1 AOI 1 – St. Cloud AASF #2 

AASF #2 has detention ponds on both the northeastern and southwestern sides of the ramps that 

are flanked by wetlands that collect runoff from AASF #2. The detention ponds are approximately 

3 feet deep and seeded with vegetation. Swales in both detention ponds carry intermittent surface 

water to storm sewers and the Elk River. The Elk River runs parallel to the Mississippi River before 

converging at the city of Elk River. Other regional surface water features include small lakes, 

tributaries, and wetlands.

PFOA, PFOS, and PFBS were detected in surface water samples collected from northeastern 

and southwestern detention ponds. These compounds were not detected in sediment at the 

facility. Based on the SI results, the ingestion pathway for surface water is considered potentially 

complete for facility workers, future construction workers, trespassers, and recreation users. The

CSM is presented in Figure 7-1. 
SOURCE PATHWAY RECEPTOR

AOI 1

Fire Suppression

System Releases

PFAS in

Surface Soil

Source

Release

Mechanism

Media Transport

and Migration

Media Exposure

Routes

Human Receptors:

Current / Future

Flow-Chart Continues

Partial / Possible Flow

Flow-Chart Stops

Incomplete Pathway

Potentially Complete Pathway

Potentially Complete Pathway

with Exceedance of SL

Site

Worker

Construction

Worker

Resident

Trespasser/

Recreational

User

Site

Worker

Construction

Worker

Resident

Trespasser/

Recreational

User

LEGEND

Figure 7-1

Conceptual Site Model

AOI 1 St. Cloud AASF #2

Potential

Off-Facility

Source Not

Under

Control of

ARNG

Human

Activities

Leaching/

Infiltration

Precipitation/

Run-Off

Subsurface

Soil

Surface

Water/

Sediment

Surface Soil

at AOI

Shallow

Groundwater

Airborne Soil

Particulate

Inhalation of

Dust

Ingestion

Ingestion

Ingestion

Ingestion

Notes:

1. The resident and recreational user

receptors refer to an off-site

resident or recreational user.

2. Dermal contact exposure pathway

is incomplete for PFAS. 7-3
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 7-4

THIS PAGE INTENTIONALLY BLANK 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 8-1

8.0 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 Summary

The SI field activities at AASF #2 were conducted from 15-17 October 2019 and 11-12 May 2020. 

The SI field activities included soil, groundwater, surface water, and sediment sampling. Field 

activities were conducted in accordance with the QAPP Addendum (AECOM, 2019b), except as 

previously noted in Section 5.7. 

To fulfill the project DQOs set forth in the approved SI QAPP Addendum (AECOM, 2019b), 

samples were collected and analyzed for a subset of PFAS by LC/MS/MS QSM 5.1 Table B-15

as follows. The 18 PFAS analyzed as part of the ARNG SI program are specified in Section 5.7

of this Report.

• Eighteen (18) soil samples from six locations;

• Six grab groundwater samples from the six temporary well locations; 

• Five sediment samples; and

• Four surface water samples, which were co-located with sediment samples. 

This information gathered during this investigation was used to determine if PFOA, PFOS, and/or 

PFBS were present at or above SLs. Additionally, the preliminary CSM was refined to assess 

whether a potentially complete pathway exists between the source and potential receptors for 

potential exposure to PFOA, PFOS, and PFBS at AOI 1, which are described in Section 7.0. 

8.2 SI Goals Evaluation

As described in Section 4.2, the SI activities were designed to achieve six main goals or DQOs. 

This section describes the SI goals and the conclusions that can be made for each based on the 

data collected during this investigation. 

1. Determine the presence or absence of PFOA, PFOS, and PFBS at or above SLs. 

PFAS contamination was confirmed to be present at the facility groundwater and surface 

water. PFAS were detected in the potential PFAS release areas, as well as near the facility 

boundary between source areas and potential drinking water receptors. However,

detections in groundwater did not exceed the SLs for PFOA, PFOS, or PFBS. 

2. Develop information to potentially eliminate a release from further consideration because 

it is determined that it poses no significant threat to human health or the environment.

The AOI 1 PFAS release area was removed from further consideration based on the 

groundwater data collected during this SI. PFOA, PFOS, and PFBS were not detected in 

groundwater or soil above the SLs; therefore, AOI 1 poses no significant threat to human 

health or the environment.

3. Determine the potential need for a removal action. 

Based on the data collected during this SI, no need for a removal action was identified. 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 8-2

4. Collect data to better characterize the release areas for more effective and rapid initiation 

of a RI, if determined necessary.

The geological data collected as part of the SI indicate an environment with variable 

permeability and conductivity. Soils range from poorly graded sand with gravel (high 

conductivity) to sandy clays (low conductivity). Sand-dominated beds range up to 20 feet 

in thickness, whereas soils with lower conductivity are deposited in thicknesses ranging 

up to 12 feet. 

Based on the data collected during this SI, no further action is recommended for AOI 1 at 

this time. 

5. Identify within 4 miles of the installation other potential PFAS sources (fire stations, major 

manufacturers, other DoD facilities) and receptors, including both groundwater and 

surface water receptors, to determine whether the ARNG is the likely source of PFAS, or 

whether there is an off-facility source of PFAS responsible for installation detections of 

PFAS (USEPA, 2005).

Based upon the evaluation of groundwater and soil results in comparison to SLs, in 

combination with the qualitative, shallow groundwater flow direction determination to the 

south, the source of PFAS contamination at the facility may or may not be the result of 

historical DoD activities. Potential adjacent sources of PFAS include the St. Cloud 

Regional Airport. According to the PA (AECOM, 2019a), semiannual nozzle testing for the 

St. Cloud firetrucks is conducted at the airport, north of the airport’s Aircraft Rescue and 

Fire Fighting Facility between the building and the ramp. During the nozzle testing, 

approximately 5 gallons of HEF mixture are released to the ground. No information was 

available on the type or concentration of foam used or stored at the facility, and no 

remediation activities are known to have occurred at this location. Additionally, the lack of 

monitoring wells between the St. Cloud Regional Airport and the AASF #2 make it difficult 

to determine the Airport as a potential upgradient source based on the perceived 

groundwater flow direction. 

6. Determine whether a potentially complete pathway exists between the source and 

potential receptors and whether ARNG is the likely source of the contamination. 

Detections of PFOA, PFOS, and PFBS in groundwater and surface water at source areas 

and near the facility boundary indicate there are potentially complete pathways for site 

workers, future construction workers, trespassers, and recreational users. 

8.3 Outcome 

Based on the preliminary CSM that was developed and revised based on the SI findings, there 

may be potential for exposure to residential drinking water receptors from sources at AASF #2

that resulted from historical DoD activities. Sample chemical analytical concentrations collected 

during this SI were compared against the SLs for PFOA and PFOS in groundwater and OSD 

screening levels for PFOS, PFOA, and PFBS in soil and groundwater. The results of the SI relative 

to the SLs are as follows: 

• PFOA and PFOS were detected in groundwater in AOI 1 near the facility boundary with 

maximum detected concentrations of 2.74 J ng/L and 1.85 J ng/L, respectively. PFOA and 

PFOS detection in groundwater were below the SLs. PFBS was not detected in groundwater 

at AOI 1.

• PFOA, PFOS, and PFBS were not detected in soil at AOI 1. 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 8-3

Table 8-1 summarizes the SI results for soil and groundwater. Based on the CSMs developed and 

revised in light of the SI findings, there is limited potential for exposure to residential drinking water 

receptors caused by DoD activities at or adjacent to the facility. 

Table 8-2 summarizes the rationale used to determine if an AOI should be considered for further 

investigation under CERCLA and undergo an RI. Based on the results of this SI, no further action 

is recommended for AOI 1 at the AASF #2 at this time. 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 8-4

THIS PAGE INTENTIONALLY BLANK
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 8-5

Table 8-1: Summary of Site Inspection Findings

AOI Potential PFAS 

Release Area

Soil – 

Source Area

Groundwater – 

Source Area

Groundwater –

Facility 

Boundary 

1 St. Cloud AASF #2

Legend:

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected

Table 8-2: Site Inspection Recommendations

AOI Description Rationale Future Action

1 St. Cloud AASF #2 Detections in groundwater and surface water. No 

exceedances of the SLs in soil or groundwater. No further action
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 8-6

THIS PAGE INTENTIONALLY BLANK
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 9-1

9.0 References

AECOM. 2018a. Final Site Inspection Programmatic Uniform Federal Policy-Quality Assurance 

Project Plan, Perfluorooctanesulfonic Acid (PFOS) and Perfluorooctanoic Acid (PFOA) 

Impacted Sites ARNG Installations, Nationwide. Contract No. W912DR-12-D0014/W912DR17F0192. 9 March.

AECOM. 2018b. Final Programmatic Accident Prevention Plan, Perfluorooctanesulfonic Acid 

(PFOS) and Perfluorooctanoic Acid (PFOA) Impacted Sites ARNG Installations, Nationwide.

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

AECOM. 2019a. Final Preliminary Assessment Report, Army Aviation Support Facility, St. Cloud, 

Minnesota, Perfluorooctanesulfonic Acid (PFOS) and Perfluorooctanoic Acid (PFOA) 

Impacted Sites ARNG Installations, Nationwide. Contract No. W912DR-12-D0014/W912DR17F0192. April. 

 AECOM. 2019b. Final Site Inspection Uniform Federal Policy-Quality Assurance Project Plan 

Addendum, Army Aviation Support Facility, St. Cloud, Minnesota, Perfluorooctanesulfonic 

Acid (PFOS) and Perfluorooctanoic Acid (PFOA) Impacted Sites ARNG Installations, 

Nationwide. Contract No. W912DR-12-D-0014/W912DR17F0192. April. 

AECOM. 2019c. Final Site Safety and Health Plan, Army Aviation Support Facility, St. Cloud, 

Minnesota, Perfluorooctanesulfonic Acid (PFOS) and Perfluorooctanoic Acid (PFOA) 

Impacted Sites ARNG Installations, Nationwide. Contract No. W912DR-12-D0014/W912DR17F0192. April. 

Assistant Secretary of Defense. 2019. Investigation Per- and Polyfluoroalkyl Substances within 

the Department of Defense Cleanup Program. United States Department of Defense. 

October.

City of St. Cloud, Minnesota. 2011. Stormwater Management Plan. December.

Cummins, J.F. and Grigal, D.F. 1981. Legend to Map Soil and Land Surface of Minnesota 1980.

Department of Soil Science, University of Minnesota. Soil Series No. 110, Miscellaneous 

Publication 11.

DA. 2016. Army Guidance to Address Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoic 

Acid (PFOA) Contamination. August.

DA. 2018. Army Guidance for Addressing Releases of Per- and Polyfluoroalkyl Substances. 4 

September.

DoD. 2018. Department of Defense (DoD) Department of Energy (DOE) Consolidated Quality 

Systems Manual (QSM) for Environmental Laboratories, Version 5.1.1. September.

DoD. 2019. General Data Validation Guidelines. Environmental Data Quality Workgroup. 4 

November. 

Guelfo, J.L. and Higgins, C.P., 2013. Subsurface transport potential of perfluoroalkyl acids ad 

aqueous film-forming foam (AFFF)-impacted sites. Environmental Science and Technology 

47(9): 4164-71.

Higgins, C. P., and R. G. Luthy, 2006. Sorption of perfluorinated surfactants on 

sediments. Environmental Science and Technology 40 (23): 7251-7256.

ITRC. 2018. Environmental Fate ant Transport for Per- and Polyfluoroalkyl Substances. March. 
Site Inspection Report

St. Cloud AASF #2, St. Cloud, Minnesota

AECOM 9-2

MNDNR. 2017. Geologic Atlas of Sherburne County, Minnesota. County Atlas Series C-32, Part 

B, Hydrogeology.

MnDot. 2006. St. Cloud Regional Airport Master Plan. 

Sherburne County Planning & Zoning Department. 2011. Comprehensive Land Use Plan 2010-

2030. September.

USACE. 2016. Technical Project Planning Process, EM-200-1-2. 26 February.

USEPA. 1980. Comprehensive Environmental Response, Compensation, and Liability Act 

(CERCLA). 

USEPA. 1994. National Oil and Hazardous Substances Pollution Contingency Plan (Final Rule). 

40 CFR Part 300; 59 Federal Register 47384. September.

USEPA. 2001. Risk Assessment Guidance for Superfund, Volume I: Human Health Evaluation 

Manual (Part D, Standardized Planning, Reporting, and Review of Superfund Risk 

Assessments). December.

USEPA. 2005. Federal Facilities Remedial Site Inspection Summary Guide. 

USEPA. 2006. Guidance on Systematic Planning using the Data Quality Objectives Process. 

February.

USEPA. 2016a. Drinking Water Health Advisory for Perfluorooctanoic Acid (PFOA). Office of 

Water (4304T). Health and Ecological Criteria Division, Washington, DC 20460. US USEPA 

Document Number: 822-R-16-005. May 2016.

USEPA. 2016b. Drinking Water Health Advisory for Perfluorooctane Sulfonate Acid (PFOS). 

Office of Water (4304T). Health and Ecological Criteria Division, Washington, DC 20460. US 

USEPA Document Number: 822-R-16-004. May.

USEPA. 2017. National Functional Guidelines for Organic Superfund Data Review. OLEM 

9355.0-136, EPA-540-R-2017-002. Office of Superfund Remediation and Technology 

Innovation. January. 

USFWS. 2019. Species by County Report, County: Sherburne County, Minnesota. Environmental 

Conservation Online System. Accessed 17 March 2020 at 

https://ecos.fws.gov/ecp0/reports/species-by-current-range-county?fips=27141

World Climate. 2018. Average Weather Data for Saint Cloud, Minnesota. Accessed 12 October 

2018 at http://www.worldclimate.com/climate/us/minnesota/saint-cloud

Xiao, F., M. F. Simcik, T. R. Halbach, and J. S. Gulliver. 2015, Perfluorooctane sulfonate (PFOS) 

and perfluorooctanoate (PFOA) in soils and groundwater of a U.S. metropolitan area: 

Migration and implications for human exposure. Water Research 72: 64-74.