FINAL

Site Inspection Report 

Decatur Army Aviation Support 

Facility #1, Illinois

Site Inspection for Perfluorooctanoic acid (PFOA), 

Perfluorooctanesulfonic acid (PFOS), Perfluorohexanesulfonic 

acid (PFHxS), Perfluorononanoic acid (PFNA), 

Hexafluoropropylene oxide dimer acid (HFPO-DA), and 

Perfluorobutanesulfonic acid (PFBS) at ARNG Installations, 

Nationwide 

July 2023

Prepared for:

Army National Guard Bureau

111 S. George Mason Drive

Arlington, VA 22204

UNCLASSIFIED
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Table of Contents

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

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

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

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

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

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

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

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

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

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

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

2.2.5 Current and Future Land Use......................................................................2-3

2.2.6 Sensitive Habitat and Threatened/ Endangered Species.............................2-3

2.3 History of PFAS Use..............................................................................................2-3

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

3.1 AOI 1 Hangar Ramp..............................................................................................3-1

3.2 Adjacent Sources ..................................................................................................3-1

3.2.1 Decatur Fire Department Station 7..............................................................3-1

3.2.2 Decatur Airport Hangars..............................................................................3-1

3.2.3 Old United Parcel Service Hangar...............................................................3-1

3.2.4 Decatur Fire Department Training Area .......................................................3-2

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

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

4.2 Information Inputs .................................................................................................4-1

4.3 Study Boundaries..................................................................................................4-1

4.4 Analytical Approach...............................................................................................4-1

4.5 Data Usability Assessment....................................................................................4-1

5. Site Inspection Activities ...............................................................................................5-1

5.1 Pre-Investigation Activities.....................................................................................5-1

5.1.1 Technical Project Planning ..........................................................................5-1

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

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

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

5.3 Temporary Well Installation and Groundwater Grab Sampling...............................5-4

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Appendix A Data Usability Assessment and Validation Reports

Appendix B Field Documentation

B1. Log of Daily Notice of Field Activities

B2. Sampling Forms

B3. Nonconformance and Corrective Action Reports

B4. Survey Data

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 Facility Location

Figure 2-2 Facility Topography

Figure 2-3 Groundwater Features

Figure 2-4 Groundwater Elevations

Figure 2-5 Surface Water Features

Figure 3-1 Area of Interest

Figure 5-1 Site Inspection Sample Locations

Figure 6-1 PFOA Detections in Soil

Figure 6-2 PFOS Detections in Soil

Figure 6-3 PFBS Detections in Soil

Figure 6-4 PFHxS Detections in Soil

Figure 6-5 PFNA Detections in Soil

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

Figure 6-7 PFHxS and PFNA Detections in Groundwater

Figure 7-1 Conceptual Site Model, AOI 1

Tables

Table ES-1 Screening Levels (Soil and Groundwater)

Table ES-2 Summary of Site Inspection Findings and Recommendations

Table 5-1 Site Inspection Samples by Medium

Table 5-2 Soil Boring Depths, Temporary Well Screen Intervals, and Groundwater 

Elevations

Table 6-1 Screening Levels (Soil and Groundwater)

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

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

Table 6-4 PFOA, PFOS, PFBS, PFNA, and PFHxS Results in Groundwater

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

% percent

°C degrees Celsius

°F degrees Fahrenheit

μg/kg micrograms per kilogram

AASF Army Aviation Support Facility

AECOM AECOM Technical Services, Inc.

AFFF aqueous film-forming foam

AOI Area of Interest

ARNG Army National Guard

bgs below ground surface 

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act 

CoC chain of custody

CSM conceptual site model

DA Department of the Army

DoD Department of Defense

DQO data quality objective

DUA data usability assessment

ELAP Environmental Laboratory Accreditation Program

EM Engineer Manual

FBO Fixed Base Operator

FedEx Federal Express

FTA Fire Training Area

GPRS Ground Penetrating Radar Systems, LLC.

HDPE high-density polyethylene 

HFPO-DA hexafluoropropylene oxide dimer acid

IDW investigation-derived waste

ILARNG Illinois Army National Guard

ISGS Illinois State Geological Survey

ISWS Illinois State Water Survey

ITRC Interstate Technology Regulatory Council

IWRA International Water Resources Association

LC/MS/MS liquid chromatography with tandem mass spectrometry

MIL-SPEC military specification

MS matrix spike

MSD matrix spike duplicates

NELAP National Environmental Laboratory Accreditation Program

ng/L nanograms per liter

OSD Office of the Secretary of Defense

PA Preliminary Assessment

PFAS per- and polyfluoroalkyl substances

PFBS perfluorobutanesulfonic acid

PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid
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PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

PID photoionization detector

PQAPP Programmatic UFP-QAPP

PVC polyvinyl chloride

QA quality assurance

QAPP Quality Assurance Project Plan

QC quality control

QSM Quality Systems Manual

SI Site Inspection

SL screening level

SOP standard operating procedure

TOC total organic carbon

TPP Technical Project Planning

UFP Uniform Federal Policy

UPS United Parcel Service

US United States

USACE United States Army Corps of Engineers

USCS Unified Soil Classification System

USEPA United States Environmental Protection Agency

USFWS United States Fish and Wildlife Service
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Army Aviation Support Facility #1, Decatur, Illinois

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Executive Summary

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

Inspections (SIs) on the current or potential historical use of per- and polyfluoroalkyl substances 

(PFAS) with a focus on the six compounds presented in the memorandum from the Office of the 

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

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

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

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

, and perfluorobutanesulfonic acid 

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

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

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

used, stored, disposed, or released historically (see Tables ES-2). The objective of the SI is to 

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

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

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

was completed at the Army Aviation Support Facility (AASF) #1 in Decatur, Illinois and determined 

further evaluation under the Comprehensive Environmental Response, Compensation, and 

Liability Act (CERCLA) is warranted for AOI 1. AASF #1 will also be referred to as the “facility” 

throughout this document. 

AASF #1 is constructed on approximately 39 acres of land in Macon County, about 5 miles east 

of Decatur, Illinois and adjacent to Decatur Regional Airport. AASF #1 supports the Illinois ARNG 

and consists of a storage hangar, repair hangar, shops, and an office area. Exterior features 

include vehicle parking areas, roads, aircraft parking and taxiways, and a 90-foot clear-span 

bridge. AASF #1 provides aviation intermediate-level and aviation unit-level aircraft maintenance 

support. 

The PA identified one AOI for investigation during the SI phase. SI sampling results from the AOI

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

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

AOI 1. 

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

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

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

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

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

individual chemical of concern in the absence of other PFAS. 
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Army Aviation Support Facility #1, Decatur, Illinois

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

Analyteb

Residential

(Soil)

(μg/kg)a 

0-2 feet bgs

Industrial/ Commercial 

Composite Worker

(Soil)

(μg/kg)a 

2-15 feet bgs

Tap Water

(Groundwater)

(ng/L)a

PFOA 19 250 6

PFOS 13 160 4 

PFBS 1,900 25,000 601 

PFHxS 130 1,600 39

PFNA 19 250 6

Notes:

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

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

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

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

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

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

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

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

AOI

Potential 

Release 

Area

Soil – 

Source Area

Groundwater – 

Source Area Future Action

1 Hangar 

Ramp Proceed to RI 

Legend:

N/A = not applicable 

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected
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1. Introduction

1.1 Project Authorization

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

(PAs) and Site Inspections (SIs) on the current or potential historical use of per- and 

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

memorandum from the Office of the Secretary of Defense (OSD) dated 6 July 2022 (Assistant 

Secretary of Defense, 2022). The six compounds listed in the OSD memorandum will be referred 

to as “relevant compounds” throughout this document and include perfluorooctanoic acid (PFOA), 

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

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

, and perfluorobutanesulfonic 

acid (PFBS) at ARNG facilities nationwide. The ARNG performed this SI at Army Aviation Support 

Facility (AASF) #1 in Decatur, Illinois. AASF #1 is also referred to as the “facility” throughout this 

document. 

The SI project elements were performed in compliance with Comprehensive Environmental 

Response, Compensation, and Liability Act (CERCLA; United States [US] Environmental 

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

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

compliance with US Department of the Army (DA) requirements and guidance for field 

investigations. 

1.2 SI Purpose

A PA was performed at AASF #1 (AECOM Technical Services, Inc. [AECOM], 2020) that identified 

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

disposed, or released historically. The objective of the SI is to identify whether there has been a 

release to the environment from the AOI identified in the PA and determine whether further 

investigation is warranted, a removal action is required to address immediate threats, or no further 

action is required based on screening levels (SLs) for the relevant compounds. 

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

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

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

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

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

individual chemical of concern in the absence of other PFAS. 
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2. Facility Background

2.1 Facility Location and Description

AASF #1 is constructed on approximately 39 acres of land in Macon County, about 5 miles east 

of Decatur, Illinois (Figure 2-1). The land is leased to the State of Illinois by the Decatur Park 

District for ARNG use. The lease was renewed in July 2021 and currently lasts for 60 months until 

June 30, 2026. AASF #1 is adjacent to Decatur Regional Airport. The facility is accessible from 

South Airport Road from the west.

AASF #1 supports the Illinois ARNG (ILARNG) and consists of a storage hangar, repair hangar, 

shops, and an office area. Exterior features include vehicle parking areas, roads, aircraft parking 

and taxiways, and a 90-foot clear-span bridge. AASF #1 provides aviation intermediate-level and 

aviation unit-level aircraft maintenance support.

2.2 Facility Environmental Setting

AASF #1 is in central Illinois, in the Till Plains Section of the Central Lowlands Province, which is 

characterized as a flat area with tabular uplands (Figure 2-2). The Till Plains region is split into 

seven sections: Rock River Hill Country, Green River Lowland, Galesburg Plain, Springfield Plain, 

Mt. Vernon Hill Country, Bloomington Ridged Plain, and Kankakee Plain. The finest sediments 

from the outwash, such as silts and clays, form bedded deposits in lakes and streams from 

dammed stream valleys created by glaciers. In low-lying areas on these till plains, water is stored

in areas where meltwaters were diked behind end moraines. The Sangamon River is the primary 

stream channel near the facility. The Sangamon River and its tributaries drain the excess water 

from the facility into Lake Decatur (Illinois State Geological Survey [ISGS], 2000).

2.2.1 Geology

AASF #1 is within the Springfield Plain, which is mostly composed of Illinoian glacial drift. This 

drift makes the surface geology of the area gently undulating, with modern shallowly entrenched 

drainage.

The surficial geology at AASF #1 consists of the Quaternary-aged Richland Loess and the 

Wedron Formation. The Richland Loess is composed primarily of silt, with sand and clay and 

ranges from about 4 to 7 feet thick. The Wedron Formation, which underlays the Richland Loess,

is a glacial till that consists of silt, sand, clay, and gravel, and it ranges from 10 to 100 feet thick 

(Bergstrom et al., 1976). Cambrian- to Pennsylvanian-aged units form the bedrock sequence 

beneath the facility. The uppermost unit is the Bond Formation, which has an average thickness 

of 200 feet and is made up of the Millersville Limestone and Shoal Creek Limestone members 

(Bergstrom et al., 1976; Reinertsen, 1991; Kolata, 2005). The Pennsylvanian bedrock layer is 

primarily made up of sandstone, siltstone, shale, limestone, coal, and underclay. This layer is 

found at AASF #1 at roughly 900 feet below ground surface (bgs). Paleozoic sedimentary strata 

in Macon County reportedly have a total thickness exceeding 7,100 feet (Reinertsen, 1991; Illinois 

State University, 2016). The geology of the facility is shown on Figure 2-3.

Based on observations made during the SI, surface and shallow subsurface soil at AASF #1 are

dominated by silt and lean clay, with minor amounts of sand and gravel observed with depth. 

These lithologic observations at AASF #1 are consistent with the understood geologic history of 

the region, which includes fine-grained, wind-blown, glacial loess underlain by unsorted glacial till

deposits. SI soil borings were completed at depths between 10 and 20 feet bgs. One boring, 

AOI01-06, was drilled to 20 feet bgs but later backfilled to approximately 10 feet bgs. Minor 

amounts of sand were observed in some of the logs in percentages that ranged from <5 percent 
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Army Aviation Support Facility #1, Decatur, Illinois

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(%) to 30%, with an approximately 4-foot layer of sand-dominated soil at the base of boring 

AOI01-06. Many of the logs also reported varying percentages (<5% to 20%) of gravel included 

in the fine-grained packages. The highest percentages of sand and gravel were observed at 

location AOI01-06; however, this boring was initially drilled to 20 feet bgs in an attempt to find 

water deeper than the very shallow perched zone, but it was later backfilled to approximately 10 

feet bgs after perched groundwater was similarly observed at other locations. Different from all 

other locations, borehole AOI01-03 was observed to be essentially dry during drilling. Soil at this 

location was composed of fines (clay and silt) for the entire 15-foot length, with trace amounts of 

gravel but no sand observed. This fines-dominated lithology may explain the lack of available 

groundwater, which was readily available after drilling at all five other locations. The lithology 

observed in the upper 10 feet of each boring appears to be relatively consistent across the facility. 

Boring logs are presented in Appendix E.

2.2.2 Hydrogeology

Groundwater at AASF #1 is encountered in continuous and discontinuous sand and gravel 

deposits less than 15 feet thick (Bergstrom et al., 1976). The general shallow groundwater flow 

direction at AASF #1 is west, toward Lake Decatur. Additionally, the Pennsylvanian-aged units 

near the facility contain groundwater resources in small quantities. In the Bond Formation, 

groundwater flows via the crevices and dissolution channels in the limestone (Bergstrom et al., 

1976). The deeper, regional aquifer is known as the Mahomet aquifer; however, it is located

approximately 8 miles north of AASF #1 and does not underlie the facility (International Water 

Resources Association [IWRA], 2003). This aquifer occupies 15 counties and is the most 

important aquifer in central and east Illinois. Within 4 miles of AASF #1, four public supply wells 

are set within the sand and gravel system aquifer and have total depths ranging from 39 to 107 

feet bgs (Illinois State Water Survey [ISWS], 2020). 

No public water supply wells are located downgradient between the facility and Lake Decatur 

(ISWS, 2020); however, multiple wells of unknown use are located downgradient of the facility. 

According to the ISGS well database, the nearest wells are located within a 0.5-miles from the 

facility boundary, and they are reportedly over 140 feet deep (ISGS, 2022). Well locations and 

groundwater flow are shown in Figure 2-3. The State of Illinois does not provide specific well type 

information (e.g., monitoring well, domestic well, industrial well, etc.). Drinking water for AASF #1

is supplied by the City of Decatur, which sources most of the drinking water from Lake Decatur 

(City of Decatur, 2018). Lake Decatur is approximately 1 mile downgradient and to the west of the 

facility (Figure 2-3). When Lake Decatur’s water level is low, a well field in DeWitt County provides 

supplemental water (City of Decatur, 2018; ISWS, 2020).

Depths to water measured in October 2021 during the SI ranged from 1.98 to 5.93 feet bgs. The 

groundwater elevation measured at AOI01-03 was not used for contouring. Unlike all other 

locations, the borehole was initially dry during drilling, and the groundwater observed after 

recharge was significantly lower than at other wells (11.45 feet bgs). Groundwater at AOI01-03 

collected in the well after approximately 40 hours of recharge time, but it is uncertain where the 

water originated from in the subsurface. Along with supporting geologic evidence, AOI01-03 is not 

believed to be representative of hydrogeologic conditions at the facility. Groundwater elevation 

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

generally to the west. In the southern-most portion of the facility, flow may be more northwesterly 

but well control in that area is limited. 

2.2.3 Hydrology

Drainage from the helicopter parking apron and hangar ramp at AASF #1 flows to the west and 

collects in a drainage ditch via overland flow and two outfalls. The drainage ditch is located outside 

of the western facility fence line, along South Airport Road. Storm sewers on the facility property 
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flow to Lake Decatur (Anderson Environmental, 2019). The hangar floor drains to an oil/water 

separator prior to discharging to the sanitary sewer that drains to the City of Decatur WWTP 

(AECOM, 2020; Anderson Environmental, 2019). Figure 2-5 shows small ponds and a stream

that appear to drain southwest to Lake Decatur and are located on the golf course to the west of 

the facility. 

Lake Decatur is the largest impoundment of the Sangamon River, with a storage capacity of 

9 billion gallons (City of Decatur, 2019). Drinking water for the City of Decatur is supplied by 

withdrawal from the lake from unknown locations (Keefer et al., 2010). The Sangamon River and 

tributaries in Macon County provide all the surface water in the county and supply about 11 billion 

gallons for industrial and municipal use annually (Reinertsen, 1991). The Sangamon River drains 

approximately 925 square miles of the watershed into Lake Decatur, with excess water 

overpassing the dam and moving farther downstream. Surface water features are presented on 

Figure 2-5. 

2.2.4 Climate 

The climate at AASF #1 is characterized by long, warm, and humid summers and freezing, windy 

winters. Cloud cover can be found all times of the year. Temperatures vary from average highs of 

64.2 degrees Fahrenheit (°F) to average lows of 43.3 °F. The average annual temperature is 

53.75 °F. Average precipitation is 40.37 inches of rain (World Climate, 2022).

2.2.5 Current and Future Land Use

AASF #1 is a controlled access facility and is adjacent to Decatur Regional Airport. The facility 

was constructed for use by the ILARNG and presently consists of a storage hangar, repair hangar, 

shops, and an office area. Exterior features include vehicle parking areas, roads, aircraft parking 

and taxiways, and a 90-foot clear-span bridge. Reasonably anticipated future land use is not 

expected to change from the current land use. 

2.2.6 Sensitive Habitat and Threatened/ Endangered Species 

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

or are listed as candidate species in Macon County, Illinois (US Fish and Wildlife Service

[USFWS], 2022). 

• Insects: Monarch butterfly, Danaus plexippus (candidate); Rusty patched bumble bee,

Bombus affinis (endangered)

• Mammals: Northern long-eared bat, Myotis septentrionalis (threatened); Indiana bat Myotis

sodalis (endangered)

• Flowering plants: Eastern prairie fringed orchid, Platanthera leucophaea (threatened)

2.3 History of PFAS Use

One AOI where AFFF may have been used or released historically was identified in the PA 

(AECOM, 2020). Tri-Max30TM extinguishers equipped with AFFF were staged at the AOI from the 

late 1990s to 2005. A description of the AOI is presented in Section 3. 
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­12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

JW

8/22/2022

8/22/2022

PROJECT Site Inspection at Decatur AASF #1, IL

8/22/2022

1:63,360

PM CM 8/22/2022 Base Map: Sources: Esri, HERE, Garmin, USGS,

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

Figure 2-1

Facility Location

Legend

Facility Boundary

0 0.5 1 2

Miles

Decatur AASF #1

^_

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­12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

JW

9/14/2022

9/14/2022

PROJECT Site Inspection at Decatur AASF #1, IL

9/14/2022

1:12,000

PM CM 9/14/2022 Base Map: USGS The National Map: National

Boundaries Dataset, 3DEP Elevation Program,

Figure 2-2

Facility Topography

Legend

Facility Boundary

0 500 1,000 2,000

Feet

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and the GIS User Community

Figure 2-3

Groundwater Features

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Figure 2-4

Groundwater Elevations

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Figure 2-5

Surface Water Features

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3. Summary of Areas of Interest

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

disposed, or released historically. Based on the PA findings, one potential release area was

identified at AASF #1 and is considered an AOI (AECOM, 2020). The potential release area is

shown on Figure 3-1. 

3.1 AOI 1 Hangar Ramp

AOI 1 is the Hangar Ramp, where four Tri-Max30TM extinguishers were staged from the late 1990s 

to 2005. The Tri-Max30TM units were stored on the hangar ramp in the paved area that surrounded 

the main hangar and led to the helicopter parking apron. The units were serviced and visually 

inspected annually by GETZ Fire Equipment Company. No AFFF was expended during 

inspections, and AFFF was never stored in bulk at the facility. In 2005, the extinguishers were 

removed and sent to Camp Lincoln, in Springfield, Illinois. Personnel interviewed during the PA 

did not recall any leaks or spills from these units (AECOM, 2020). 

3.2 Adjacent Sources

Six off-facility, potential sources, which are not associated with ARNG activities, were identified 

adjacent to AASF #1 during the PA. The adjacent potential sources are shown on Figure 3-1 and 

described in the following sections for informational purposes only. 

3.2.1 Decatur Fire Department Station 7

The Decatur Fire Department Station 7 is the primary contact for emergency response at the 

AASF. This is an active fire station containing emergency response vehicles and equipment. The 

Decatur Fire Department is located south of AASF and due to the location of the building, it was

identified as a potential adjacent source of PFAS contamination. It is suspected that the 

emergency response vehicles and equipment may possibly store AFFF, but it is unknown if they 

do or if there have been any releases. Additionally, it is unknown if nozzle testing occurred at 

Decatur Fire Department Station 7.

3.2.2 Decatur Airport Hangars 

Located to the south of the facility, there are three hangars operated by the Decatur Airport: a 

Maintenance Hangar, a Fixed Based Operator (FBO) Hangar and Corporate Hangars. There are 

also several storage hangars located at the Decatur Airport, one directly north of the maintenance 

hangar, and another directly north of the Decatur Fire Department Station 7. As it is unknown 

whether there are fire suppression systems in any of the hangars, or if AFFF has been used for 

training or as a fire suppressant at any time, the hangars have been classified as potential 

adjacent sources. 

3.2.3 Old United Parcel Service Hangar 

Approximately 1 mile southwest of the facility, adjacent to the Decatur Fire Department training 

area, there is an old United Parcel Service (UPS) Hangar. The hangar currently has four Purple 

K extinguishers stored in its vicinity. It is unknown if AFFF has been stored or released at this 

location; therefore, it is considered a potential adjacent source.
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3.2.4 Decatur Fire Department Training Area

The Decatur Fire Department Station 7 has a FTA at the airport located south of the runways in 

the ramp area adjacent to the Old UPS Hangar. It is unknown if AFFF was used during training 

events, the time period of events, how often the training events occurred, or the type and volume 

of fire suppression materials used during training events. Due to the uncertainty of activities at 

the FTA, it is considered a potential adjacent source. Additionally, it is unknown if nozzle testing 

occurs at Decatur Fire Department Station 7.
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Figure 3-1

Area of Interest

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4. Project Data Quality Objectives

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

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

whether there has been a release to the environment at the AOI identified in the PA. For each 

AOI, ARNG determines if further investigation is warranted, a removal action is required to 

address immediate threats, or whether no further action is warranted. This SI evaluated 

groundwater and soil for presence or absence of relevant compounds at each of the sampled 

AOI.

4.1 Problem Statement

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

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

SLs are presented in Section 6.1 of this report. 

4.2 Information Inputs

Primary information inputs included:

• The PA for Decatur AASF #1 (AECOM, 2020);

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

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

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

parameters measured at the time of sampling.

4.3 Study Boundaries

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

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

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

owner(s). The SI was bounded vertically by the first encountered groundwater at a given borehole.

The SI was conducted in the fall and was temporally bounded (i.e., seasonally restricted) to avoid field 

work during the winter months. 

4.4 Analytical Approach

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

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

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

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

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

4.5 Data Usability Assessment

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

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

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

methods, the assessment determines whether project execution and the resulting data have met 

installation-specific DQOs. Both sampling and analytical activities are considered to assess 
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whether the collected data are of the right type, quality, and quantity to support the decisionmaking (DoD, 2019a; DoD, 2019b; USEPA, 2017). 

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

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

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

requirements of the SI QAPP Addendum (AECOM, 2021a). 
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5. Site Inspection Activities

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

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

in accordance with the following approved documents: 

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

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

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

• Final Preliminary Assessment Report, Decatur Army Aviation Support Facility #1, Illinois

dated August 2020 (AECOM, 2020);

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

Decatur Army Aviation Support Facility #1, Illinois dated October 2021 (AECOM, 2021a);

and

• Final Site Safety and Health Plan, Decatur Army Aviation Support Facility #1, Illinois dated

October 2021 (AECOM, 2021b).

The SI field activities consisted of utility clearance, rotosonic (sonic) soil boring, soil sample 

collection, temporary monitoring well installation and subsequent abandonment, grab groundwater 

sample collection, and land surveying. Utility clearance was performed on 21 October 2021 and all 

other field activities were conducted from 25 to 28 October 2021, in accordance with the SI QAPP 

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

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

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

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

• Eleven (11) soil samples from six boring locations;

• Six grab groundwater samples from six temporary wells;

• Thirteen (13) quality assurance (QA)/quality control (QC) samples.

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

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

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

in Appendix B1. Sampling forms are provided in Appendix B2, Nonconformance and Corrective 

Action Reports are provided in Appendix B3, and land survey data are provided in Appendix 

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

5.1 Pre-Investigation Activities

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

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

water. Details for each of these activities are presented below.

5.1.1 Technical Project Planning

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

(USACE, 2016) defines four phases to project planning: 1.) defining the project phase; 2.) 

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

collection plan. The process encourages stakeholder involvement in the SI, beginning with 
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defining overall project objectives, including DQOs, and formulating a sampling approach to 

address the AOI identified in the PA. 

A combined TPP Meeting 1 and 2 was held on 15 September 2021, prior to SI field activities. The 

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

stakeholders for this SI include the ARNG, ILARNG, USACE, and Illinois Environmental 

Protection Agency. Stakeholders were provided the opportunity to make comments on the 

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

of the combined TPP Meeting 1 and 2 was memorialized in the SI QAPP Addendum (AECOM, 

2021a).

A TPP Meeting 3 will be held [date to be determined] 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, Cascade Technical Services, LLC. placed a ticket with the 

“J.U.L.I.E.” Illinois utility clearance provider to notify them of intrusive work on 12 October 2021.

However, because the AASF is a private facility, the participating “J.U.L.I.E.” locators did not clear 

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

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

utility clearance of the proposed boring locations on 21 October 2021 with input from the AECOM 

field team and Decatur AASF #1 facility staff. General locating services and ground-penetrating 

radar were used to complete the clearance. Additionally, the first 5 feet of each boring were precleared using a hand auger to verify utility clearance in the shallow subsurface where utilities 

would typically be encountered.

5.1.3 Source Water and Sampling Equipment Acceptability

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

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

potable water source (DECA-DECON-01) at Decatur AASF #1 was collected on 12 August 2021, 

prior to mobilization, and analyzed by LC/MS/MS compliant with QSM 5.3 Table B-15. The results 

of the decontamination water sample are provided in Appendix F. A discussion of the results is 

presented in the DUA in Appendix A.

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

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

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

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

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

member regarding the allowable materials within the sampling environment.

5.2 Soil Borings and Soil Sampling

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

(AECOM, 2021a). A hand auger was used to collect soil from the top 5 feet of the boring, in 

accordance with AECOM utility clearance procedures. A GeoProbe® 8140DT sonic drilling

sampling system with a 4-inch diameter core barrel, and a 6-inch diameter override casing was 

used to collect continuous soil cores to the target depth. The soil boring locations are shown on 

Figure 5-1, and depths are provided Table 5-1. 
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In general, two discrete soil samples were collected from the vadose zone for chemical analysis 

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

approximately 2 feet above the groundwater table. Due to shallow groundwater encountered less 

than 6 feet bgs at five of the six locations, only two soil samples were collected per boring, in 

accordance with the QAPP Addendum (AECOM, 2021a). One location, AOI01-03, was drilled to 

15 feet bgs but was dry during drilling; due to the shallow groundwater observed at other locations, 

the 13- to 15-foot interval was sampled, and no third sample was taken. At location AOI01-06, the 

shallow subsurface and grain size soil samples were lost during or after shipment to the laboratory 

(as discussed in Section 5.8), so only surface soil was analyzed at this location.

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

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

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

Observations and measurements were recorded on sampling forms 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. 

Based on observations made during the SI, surface and shallow subsurface soil at AASF #1 are

dominated by silt and lean clay, with lesser amounts of sand and gravel observed with depth. 

These lithologic observations at AASF #1 are consistent with the understood geologic history of 

the region, which includes fine-grained, wind-blown, glacial loess underlain by unsorted glacial till

deposits. SI soil borings were completed at depths between 10 and 20 feet bgs. 

Lesser amounts of sand were observed in some of the logs in percentages that ranged from <5% 

to 30%, with an approximately 4-foot layer of sand-dominated soil at the base of boring AOI01-06.

Many of the logs also reported varying percentages (<5% to 20%) of gravel included in the finegrained packages. The highest percentages of sand and gravel were observed at location AOI01-

06; however, this boring was initially drilled to 20 feet bgs in an attempt to find water deeper than 

the very shallow perched zone, but it was later backfilled to approximately 10 feet bgs after 

perched groundwater was similarly observed at other locations. Different from all other locations, 

borehole AOI01-03 was observed to be essentially dry during drilling. Soil at this location was 

composed of fines (clay and silt) for the entire 15-foot length, with trace amounts of gravel, but no 

sand observed. This fines-dominated lithology may explain the lack of available groundwater, 

which was readily available after drilling at all five other locations. The lithology observed in the 

upper 10 feet of each boring appears to be relatively consistent across the facility. 

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

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

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

to the laboratory and analyzed by LC/MS/MS compliant with QSM 5.3 Table B-15, total organic 

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

SI QAPP Addendum (AECOM, 2021a). 

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

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

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

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

samples, equipment rinsate blanks were collected at a rate of 5% and analyzed for the same 

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

samples were preserved at or below 6 degrees Celsius (°C) during shipment.

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

accordance with the SI QAPP Addendum (AECOM, 2021a) using bentonite chips at completion 
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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® 8140DT dual-tube sampling system. Once 

the borehole was advanced to the desired depth, wherever conditions allowed, a temporary well 

was constructed of a 5-foot section of 2-inch Schedule 40 poly-vinyl chloride (PVC) 0.01-slot sized

screen with sufficient casing to reach ground surface. New PVC pipe and screen were used to 

avoid cross contamination between locations. The screen intervals for the temporary wells are 

provided in Table 5-2.

The temporary wells were allowed to recharge after installation before collection of groundwater 

samples. Unlike all other locations, AOI01-03 was initially dry during drilling, and the groundwater 

observed after recharge was significantly lower than at other wells (11.45 feet bgs). Groundwater 

at AOI01-03 collected in the well after approximately 40 hours of recharge time, but it is uncertain 

what depth interval the groundwater originated from in the subsurface. After the recharge period, 

all 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, and oxidation-reduction potential) were measured 

using a water quality meter and recorded on the field sampling form (Appendix B2) before each 

grab sample was collected. 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. Samples were packaged on ice and 

transported via FedEx under standard CoC procedures to the laboratory and analyzed by 

LC/MS/MS compliant with QSM 5.3 Table B-15 in accordance with the SI QAPP Addendum 

(AECOM, 2021a).

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

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

same parameters as the accompanying samples. One field reagent blank was collected in 

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

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

Temporary wells were abandoned in accordance with the SI QAPP Addendum (AECOM, 2021a) 

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 Synoptic Water Level Measurements

A synoptic groundwater gauging event was performed on 27 October 2021. Groundwater 

elevation measurements were collected from temporary monitoring wells, except as discussed in 

Section 5.8. Water level measurements were taken from the northern side of the well casing. A 

groundwater flow contour map is provided in Figure 2-4. Groundwater elevation data are provided 

in Table 5-2. As discussed in Sections 2.2.2 and 5.3, the groundwater elevation measured at 

AOI01-03 was excluded from contouring, as it was much lower than at other wells and may not 

be representative of shallow groundwater at the facility.

5.5 Surveying

The northern side of each well casing was surveyed by Illinois-licensed land surveyors following 

guidelines provided in the SOPs in the SI QAPP Addendum (AECOM, 2021a). Survey data from 
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the newly installed wells on the facility were collected on 27 October 2021 in the applicable 

Universal Transverse Mercator zone projection with North American Datum 83 datum (horizontal) 

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

Appendix B4. 

5.6 Investigation-Derived Waste

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

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

accordance with the SI QAPP Addendum (AECOM, 2021a) and with the DA 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 characteristics of the associated soil 

samples collected from that source location. 

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

containerized in a properly labelled 55-gallon drum and stored in a secure location onsite 

identified by the AASF #1 Environmental Manager and ILARNG. The liquid IDW was not sampled 

and assumes the characteristics of the associated groundwater samples collected from the 

source locations. Based on laboratory results, containerized liquid IDW will be managed and 

disposed by ARNG under a separate contract for Treating Liquid Investigation-Derived Material (purge 

water, drilling water, and decontamination fluids) (EA Engineering, Science, and Technology, Inc., 

2021).

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

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

activities were disposed of at a licensed solid waste landfill.

5.7 Laboratory Analytical Methods

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

Coast in Baton Rouge, Louisiana, a DoD ELAP and NELAP certified laboratory. Soil samples 

were also analyzed for TOC using USEPA Method 9060A and pH by USEPA Method 9045D. 

5.8 Deviations from SI QAPP Addendum

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

documentation. The deviations are noted below and are documented in Nonconformance and 

Corrective Action Reports (Appendix B3): 

• Upon review of field documentation, it was discovered that the midpoint shallow

subsurface soil sample collected at AOI01-06, AOI01-06-SB-03-05, was missing from

the cooler sent to the laboratory, although it was collected and documented in the CoC.

Therefore, data are available only for the surface soil sample collected at AOI01-06.

However, DQOs for soil sampling at this location were still met, as discussed in the DUA 

(Appendix A).

• A grain size sample taken in the deep subsurface soil, AOI01-06-SB-18-19, was

mistakenly discarded by the laboratory and not analyzed. This sample was intended to

characterize fine-grained content of soil below the perched water-bearing zone. This

well was later backfilled to approximately 10 feet bgs prior to temporary well

construction.
Site Inspection Report

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 5-6

• During the last day of SI field activities, after the well survey was completed, well 

abandonment began prior to synoptic gauging completion. Temporary well AOI01-06 

was not gauged synoptically (i.e., within 24 hours) with the other five wells, as the casing 

had already been pulled. The groundwater elevation and depth to water for AOI01-06 

used in this report reflect the depth to water immediately prior to purging and sampling 

groundwater. However, all six wells were gauged within a 27-hour window. The 

groundwater elevation of AOI01-06 at the time of sampling is consistent with 

groundwater levels observed at the other locations and show a general flow direction 

to the west.
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, Decatur AASF #1, Illinois

Sample Identification

Sample

Collection 

Date/Time

Sample Depth 

(feet bgs)

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

Comments

AOI01-01-SB-00-02 10/25/2021 12:18 0-2 x

AOI01-01-SB-2.75-4.75 10/27/2021 12:20 2.75-4.75 x

AOI01-01-SB-2.75-4.75-D 10/27/2021 12:20 2.75-4.75 x Duplicate

AOI01-02-SB-00-02 10/27/2021 9:25 0-2 x

AOI01-02-SB-00-02-D 10/27/2021 9:25 0-2 x Duplicate

AOI01-02-SB-03-05 10/27/2021 9:35 3-5 x

AOI01-03-SB-00-02 10/26/2021 15:50 0-2 x x x

AOI01-03-SB-00-02-D 10/26/2021 15:50 0-2 x x x Duplicate

AOI01-03-SB-00-02-MS 10/26/2021 15:50 0-2 x x x MS

AOI01-03-SB-00-02-MSD 10/26/2021 15:50 0-3 x x x MSD

AOI01-03-SB-13-15 10/27/2021 16:00 13-15 x

AOI01-04-SB-00-02 10/26/2021 14:03 0-2 x

AOI01-04-SB-02-04 10/26/2021 14:45 2-4 x

AOI01-05-SB-00-02 10/26/2021 9:52 0-2 x

AOI01-05-SB-02-04 10/26/2021 10:04 2-4 x

AOI01-06-SB-00-02 10/25/2021 14:45 0-2 x

AOI01-06-SB-03-05* 10/25/2021 16:10 3-5 x not analyzed

AOI01-06-SB-18-19** 10/25/2021 16:20 18-19 x not analyzed

AOI01-01-GW 10/27/2021 17:21 NA x

AOI01-02-GW 10/27/2021 15:20 NA x

AOI01-03-GW 10/28/2021 8:30 NA x

AOI01-04-GW 10/27/2021 10:07 NA x

AOI01-04-GW-D 10/27/2021 10:07 NA x Duplicate

AOI01-04-GW-MS 10/27/2021 10:07 NA x MS

AOI01-04-GW-MSD 10/27/2021 10:07 NA x MSD

AOI01-05-GW 10/26/2021 15:30 NA x

AOI01-06-GW 10/26/2021 13:29 NA x

DECA-ERB-01 10/27/2021 14:45 NA x from hand auger

DECA-ERB-02 10/27/2021 14:55 NA x from sonic rig shoe

DECA-FRB-01 10/27/2021 14:25 NA x FRB

DECA-DECON-01 8/12/2021 13:00 NA x from spigot

DECA-DECON-02 10/27/2021 15:05 NA x from decon setup

Notes:

* Sample AOI01-06-SB-03-05 was not analyzed as sample was lost during transit to laboratory.

** Grain Size sample AOI01-06-SB-18-19 was not analyzed as it was mistakenly discarded by laboratory prior to analysis.

AASF = Army Aviation Support Facility

ASTM = American Society for Testing and Materials

bgs = below ground surface

ERB = equipment rinsate blank

FD = field duplicate

FRB = field reagent blank

LC/MS/MS = Liquid Chromatography Mass Spectrometry

MS/MSD = matrix spike/ matrix spike duplicate

QSM = Quality Systems Manual

TOC = total organic carbon

USEPA = United States Environmental Protection Agency

Soil Samples

Groundwater Samples

Quality Control Samples

AECOM 5-7
Site Inspection Report

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 5-8

THIS PAGE INTENTIONALLY BLANK
Table 5-2

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

Site Inspection Report, Decatur AASF #1, Illinois

Area of 

Interest

Boring 

Location

Soil Boring 

Depth 

(feet bgs)

Temporary Well 

Screen Interval1

(feet bgs)

Top of Casing 

Elevation 

(feet NAVD88)

Ground Surface 

Elevation 

(feet NAVD88)

Depth to 

Water

(feet btoc)

Dept

Wa

(feet 

AOI01-01 10 4.92 - 9.92 674.31 673.73 4.44 3.8AOI01-02 10 4.5 - 9.5 673.08 672.44 6.58 5.9AOI01-03 15 10 - 15 671.38 670.77 12.06 11AOI01-04 10 4.5 - 9.5 668.93 668.04 4.44 3.5AOI01-05 10 4 - 9 668.47 667.66 2.79 1.9AOI01-06 20 5.3 - 10.3 669.94 669.38 2.59 2.0

Notes:

1 Temporary well screen set above total depth to capture groundwater interfaceAASF = Army Aviation Support Facility

bgs = below ground surfacebtoc = below top of casingNA = not applicableNAVD88 = North American Vertical Datum 1988

1

AECOM 
Site Inspection Report

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 5-10

THIS PAGE INTENTIONALLY BLANK
?!

?!

?!

?!

?!

?!

AOI 1

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

AOI01-06

­12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

JW

9/14/2022

9/14/2022

PROJECT Site Inspection at Decatur AASF #1, IL

9/14/2022

1:2,040

PM CM 9/14/2022 Base Map: Source: Esri, Maxar, Earthstar Geographics,

and the GIS User Community

Figure 5-1

Site Inspection Sample Locations

Legend

?! Soil Boring/Temporary Monitoring Well

Area of Interest

Facility Boundary

Groundwater Flow Direction

0 85 170 340

Feet

AECOM 5-11
Site Inspection Report

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 5-12

THIS PAGE INTENTIONALLY BLANK
Site Inspection Report

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 6-1

6. Site Inspection Results

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

presented in Section 6.1. A discussion of the results is provided in Section 6.3. Table 6-2 through 

Table 6-4 present results in soil or groundwater for the relevant compounds. Tables that contain 

all results are provided in Appendix F, and the laboratory reports are provided in Appendix G. 

6.1 Screening Levels

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

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

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

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

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

The SLs established in the OSD memorandum apply to the five compounds presented on Table 

6-1 below.

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

Analyteb

Residential

(Soil)

(μg/kg)a 

0-2 feet bgs

Industrial/ 

Commercial 

Composite 

Worker

(Soil)

(μg/kg)a 

2-15 feet bgs

Tap Water

(Groundwater)

(ng/L)a

PFOA 19 250 6 

PFOS 13 160 4 

PFBS 1,900 25,000 601 

PFHxS 130 1,600 39

PFNA 19 250 6 

Notes:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 6-2

6.2 Soil Physicochemical Analyses

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

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

of the TOC and pH sampling. 

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

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

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

effects, electrostatic interactions, and interfacial behaviors. At relevant environmental pH values, 

certain PFAS are present as organic anions and are therefore relatively mobile in groundwater 

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

soil or sediment (Higgins and Luthy, 2006; Guelfo and Higgins, 2013). When sufficient organic 

carbon is present, organic carbon normalized distribution coefficients (Koc values) can help in 

evaluating transport potential, though other geochemical factors (for example, pH and presence 

of polyvalent cations) may also affect PFAS sorption to solid phases (ITRC, 2018).

6.3 AOI 1 

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

AOI 1: Hangar Ramp. The soil and groundwater results are summarized on Table 6-2 through 

Table 6-4. Soil and groundwater results are presented on Figure 6-1 through Figure 6-7. 

6.3.1 AOI 1 Soil Analytical Results

Figure 6-1 through Figure 6-5 present the ranges of detections in soil. Table 6-2 and Table 6-3

summarize the soil results. 

Soil was sampled from the surface interval (0 to 2 feet bgs) from boring locations AOI01-01 

through AOI01-06. Shallow subsurface soil (between 2 and 15 feet bgs) was sampled from boring 

locations AOI01-01 through AOI01-05. In surface soil, PFOA, PFOS, PFHxS, PFNA, and PFBS 

were detected at concentrations below their SLs as listed below. The maximum detected 

concentrations for all five compounds were observed at the southernmost location, AOI01-01. At 

the two northernmost sampling locations, AOI01-05 and AOI01-06, PFOS (at AOI01-05) was the 

only analyte detected. 

• PFOA was detected in three borings at concentrations up to 0.774 J micrograms per

kilogram (μg/kg).

• PFOS was detected in five borings at concentrations up to 2.22 μg/kg.

• PFHxS and PFNA were detected in four borings at concentrations up to 0.419 J μg/kg.

• PFBS was detected at two locations, with a maximum concentration of 0.029 J μg/kg.

In shallow subsurface soil, PFOA, PFOS, PFHxS, PFNA, and PFBS were detected below their 

SLs; concentrations ranged from 0.058 J μg/kg to 0.837 J μg/kg. All detections were observed at 

AOI01-01 and AOI01-04.

6.3.2 AOI 1 Groundwater Analytical Results 

Figure 6-6 and Figure 6-7 present the ranges of detections in groundwater. Table 6-4 

summarizes the groundwater results. 

Groundwater was sampled from temporary monitoring wells AOI01-01 through AOI01-06 with 

detections as follows:
Site Inspection Report

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 6-3

• PFOA was detected above the SL of 6 nanograms per liter (ng/L) at 19.2 ng/L in

AOI01-01 and 18.2 ng/L in AOI01-04.

• PFOS was detected above the SL of 4 ng/L in three wells (AOI01-01, AOI01-03, and

AOI01-04) at concentrations ranging from 7.03 ng/L to 86.6 ng/L.

• PFHxS at 69.6 ng/L and PFNA at 6.33 ng/L were detected above their respective SLs

of 39 ng/L and 6 ng/L at AOI01-04.

• PFBS was detected below the SL of 601 ng/L, with concentrations ranging from 0.933

J ng/L to 6.00 ng/L.

All exceedances of the SLs were observed at locations AOI01-03 and AOI01-04, which are 

situated to the west of AOI 1, and at AOI01-01, which is upgradient of AOI 1. AOI01-01 is along 

the southern boundary at the closest location to potential off-facility AFFF sources that were 

identified in the PA south of the AASF. 

6.3.3 AOI 1 Conclusions

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

below respective SLs. PFOA, PFOS, PFHxS, and PFNA were detected in groundwater, at

concentrations above their SLs. Based on the exceedances of the SLs in groundwater, further 

evaluation at AOI 1 is warranted. 
Site Inspection Report

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 6-4

THIS PAGE INTENTIONALLY BLANK
Table 6-2

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

Site Inspection Report, Decatur AASF #1

Analyte OSD Screening 

Level a

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

PFBS 1900 0.029 J ND U ND U ND U ND U 0.022 J ND U ND U

PFHxS 130 0.419 J ND UJ 0.060 J ND UJ 0.035 J 0.041 J ND U ND U

PFNA 19 0.287 J ND UJ 0.065 J ND UJ 0.050 J 0.027 J ND U ND U

PFOA 19 0.774 J ND UJ 0.098 J ND UJ 0.081 J ND U ND U ND U

PFOS 13 2.22 0.062 J 0.200 J 0.253 J 0.597 J 0.305 J 0.066 J ND U

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AASF Army Aviation Support Facility

U = The analyte was not detected at a level greater than or equal to the adjusted DL AOI Area of Interest

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

DL detection limit

ft feet

HQ hazard quotient

ID identification

LCMSMS liquid chromatography with tandem 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

μg/kg micrograms per kilogram

Area of Interest

Sample ID

Sample Date

Depth

AOI01-01-SB-00-02

10/25/2021

0-2 ft

10/26/2021

0-2 ft

AOI01-02-SB-00-02

10/27/2021

0-2 ft

AOI01-02-SB-00-02-D

10/27/2021

0-2 ft

a. Assistant Secretary of Defense, July 2022. Risk Based Screening Levels Calculated for PFOA, PFOS, PFBS, PFHxS, and PFNA in Groundwater or Soil using 

USEPA’s Regional Screening Level Calculator. HQ=0.1, May 2022. Soil screening levels based on residential scenario for incidental ingestion of contaminated soil.

AOI01

AOI01-06-SB-00-02

10/25/2021

0-2 ft

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

AOI01-04-SB-00-02

10/26/2021

0-2 ft

AOI01-05-SB-00-02

10/26/2021

0-2 ft

AOI01-03-SB-00-02

10/26/2021

0-2 ft

AOI01-03-SB-00-02-D

AECOM 6-5
Table 6-3

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

Site Inspection Report, Decatur AASF#1

Analyte OSD Screening 

Level a

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

PFBS 25000 ND U ND U ND U ND U 0.093 J ND U

PFHxS 1600 0.058 J 0.106 J ND U ND U 0.338 J ND U

PFNA 250 0.059 J 0.088 J ND U ND U ND U ND U

PFOA 250 0.101 J 0.288 J ND U ND U ND U ND U

PFOS 160 0.713 J 0.837 J ND U ND U 0.215 J ND U

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AASF Army Aviation Support Facility

U = The analyte was not detected at a level greater than or equal to the adjusted DL AOI Area of Interest

D duplicate

DL detection limit

ft feet

HQ hazard quotient

ID identification

LCMSMS liquid chromatography with tandem 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

μg/kg micrograms per kilogram

10/27/2021

3-5 ft

Area of Interest

Sample ID

Sample Date

Depth

AOI01-01-SB-02.75-04.75

10/27/2021

2.75-4.75 ft

a. Assistant Secretary of Defense, July 2022. Risk Based Screening Levels Calculated for PFOA, PFOS, PFBS, PFHxS, and PFNA in Groundwater or Soil using USEPA’s Regional

Screening Level Calculator. HQ=0.1, May 2022. Soil screening levels based on industrial/commercial composite worker scenario for incidental ingestion of contaminated soil.

AOI01

AOI01-05-SB-02-04

10/26/2021

2-4 ft

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

AOI01-03-SB-13-15

10/27/2021

13-15 ft

AOI01-04-SB-02-04

10/26/2021

2-4 ft

AOI01-01-SB-02.75-04.75-D

10/27/2021

2.75-4.75 ft

AOI01-02-SB-03-05

AECOM 6-6
Table 6-4

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

Site Inspection Report, Dectaur AASF #1

Analyte OSD Screening 

Level a

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

PFBS 601 4.72 3.01 J 4.10 6.00 5.96 0.933 J ND U

PFHxS 39 31.3 14.9 26.3 69.5 69.6 1.59 J 1.38 JPFNA 6 5.41 ND U ND U 6.15 6.33 ND U ND UPFOA 6 19.2 ND U 3.23 J 18.2 17.9 2.33 J ND UPFOS 4 51.6 1.08 J 7.03 85.0 86.6 2.19 J 2.06 J

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acidPFOA perfluorooctanoic acidPFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AASF Army Aviation Support FacilityU = The analyte was not detected at a level greater than or equal to the adjusted DL AOI Area of Interest

D duplicateDL detection limitGW groundwaterHQ hazard quotientID identificationLCMSMS liquid chromatography with tandem mLOD limit of detectionND analyte not detected above the LODOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierUSEPA United States Environmental Protecting/l nanogram per liter

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

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

AOI01-05-GW

10/26/2021

AOI01-06-GW

10/26/2021

AOI01-04-GW

10/27/2021

AOI01-04-GW-D

10/27/2021

AOI01-02-GW

10/27/2021

AOI01-03-GW

10/28/2021

Area of Interest

Sample ID

Sample Date

AOI01-01-GW

10/27/2021

AOI01

AECOM 
Site Inspection Report

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 6-8

THIS PAGE INTENTIONALLY BLANK
AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

AOI01-06

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

PROJECT

Figure 6-1

PFOA Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

Site Inspection at Decatur AASF #1, IL

8/22/2022

8/22/2022

8/22/2022

MS

EB

CM

GIS BY

CHK BY

PM

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

8/22/2022

1:3,064

Legend

Facility Boundary

0 85 170 340

Feet ­

Shallow Intermediate

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

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

PFOA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

AECOM 6-9
AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

AOI01-06

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

PROJECT

Figure 6-2

PFOS Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

Site Inspection at Decatur AASF #1, IL

8/22/2022

8/22/2022

8/22/2022

MS

EB

CM

GIS BY

CHK BY

PM

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

8/22/2022

1:3,064

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

Legend

Facility Boundary

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

0 85 170 340

Feet ­

Shallow Intermediate

PFOS Results (μg/Kg)

ND

>ND - 13

>13 - 160

>160 - 1,600

>1,600

AECOM 6-10
AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

AOI01-06

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

PROJECT

Figure 6-3

PFBS Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

Site Inspection at Decatur AASF #1, IL

8/22/2022

8/22/2022

8/22/2022

MS

EB

CM

GIS BY

CHK BY

PM

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

8/22/2022

1:3,064

Legend

Facility Boundary

0 85 170 340

Feet ­

Shallow Intermediate

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

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

PFBS Results (μg/Kg)

ND

>ND - 10

>10 - 1,900

>1,900 - 25,000

>25,000

AECOM 6-11
AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

AOI01-06

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

PROJECT

Figure 6-4

PFHxS Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

Site Inspection at Decatur AASF #1, IL

8/22/2022

8/22/2022

8/22/2022

MS

EB

CM

GIS BY

CHK BY

PM

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

8/22/2022

1:3,064

Legend

Facility Boundary

0 85 170 340

Feet ­

Shallow Intermediate

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

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

PFHxS Results (μg/Kg)

ND

>ND - 10

>10 - 130

>130 - 1,600

>1,600

AECOM 6-12
AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

AOI01-06

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

PROJECT

Figure 6-5

PFNA Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

Site Inspection at Decatur AASF #1, IL

8/22/2022

8/22/2022

8/22/2022

MS

EB

CM

GIS BY

CHK BY

PM

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

8/22/2022

1:3,064

Legend

Facility Boundary

0 85 170 340

Feet ­

Shallow Intermediate

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

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

PFNA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

AECOM 6-13
AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

AOI01-06

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

AOI01-06

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

AOI01-06

PROJECT

Figure 6-6

PFOA, PFOS, and PFBS Detections in Groundwater

12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

Site Inspection at Decatur AASF #1, IL

10/5/2022

10/5/2022

10/5/2022

MS

EB

CM

GIS BY

CHK BY

PM

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

10/5/2022

1:2,405

0 100 200 400

Feet ­ Legend

Facility Boundary

Groundwater Flow Direction

PFOA PFOS PFBS

PFOA Results (ng/L)

ND

>ND - 6

>6 - 40

>40 - 70

>70

PFOS Results (ng/L)

ND

>ND - 4

>4 - 40

>40 - 70

>70

PFBS Results (ng/L)

ND

>ND - 100

>100 - 601

>601 - 2,000

>2,000

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

AECOM 6-14
AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

AOI01-06

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI01-05

AOI01-06

PROJECT

Figure 6-7

PFHxS and PFNA Detections in Groundwater

12420 Milestone Center Drive

Germantown, MD 20876

CLIENT

REVISED

SCALE

ARNG

Site Inspection at Decatur AASF #1, IL

9/14/2022

9/14/2022

9/14/2022

MS

EB

CM

GIS BY

CHK BY

PM

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

9/14/2022

1:2,400

0 100 200 400

Feet ­ Legend

Facility Boundary

Groundwater Flow Direction

PFHxS PFNA

PFHxS Results (ng/L)

ND

>ND - 39

>39 - 100

>100 - 1,000

>1,000

PFNA Results (ng/L)

ND

>ND - 6

>6 - 100

>100 - 1,000

>1,000

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

AECOM 6-15
Site Inspection Report

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 6-16

THIS PAGE INTENTIONALLY BLANK
Site Inspection Report

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 7-1

7. Exposure Pathways

The CSM for AOI 1, revised based on the SI findings, are presented on Figure 7-1. Please note 

that while the CSM discussion assists in determining if a receptor may be impacted, the decision

to move from SI to Remedial Investigation (RI) or interim action is determined based upon 

exceedances of the SLs for the relevant compounds and whether the release is more than likely 

attributable to the DoD. A CSM presents the current understanding of the site conditions with 

respect to known and suspected sources, potential transport mechanisms and migration 

pathways, and potentially exposed human receptors. A human exposure pathway is considered 

potentially complete when the following conditions are present:

1. Contaminant source;

2. Environmental fate and transport;

3. Exposure point;

4. Exposure route; and

5. Potentially exposed populations.

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

circle symbol to represent an incomplete exposure pathway. Areas with an incomplete pathway 

generally warrant no further action. However, the pathway is considered potentially complete if the 

relevant compounds are detected, in which case the CSM figure uses a half-filled circle symbol to

represent a potentially complete exposure pathway. Additionally, a completely filled circle symbol is 

used to indicate when a potentially complete exposure pathway has detections of relevant 

compounds above the SLs. Areas with an identified potentially complete pathway that have 

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

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

recommendation for future study in an RI or no action at this time is based on the comparison of 

the SI analytical results for the relevant compounds to the SLs.

In general, the potential routes of exposure to the relevant compounds are ingestion and 

inhalation. Human exposure via the dermal contact pathway may occur, and current risk practice 

suggests it is an insignificant pathway compared to ingestion; however, exposure data for dermal 

pathways are sparse and continue to be the subject of toxicological study. The receptors 

evaluated are consistent with those listed in USEPA guidance for risk screening (USEPA, 2001). 

Receptors at the facility include site workers (e.g., facility staff and visiting soldiers), construction 

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

boundary, and recreational users outside of the facility boundary. No construction activities were 

observed to be occurring at the time of the SI field work; therefore, all pathways to present 

construction workers are considered incomplete. 

7.1 Soil Exposure Pathway

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

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

7.1.1 AOI 1 

From the late 1990s to 2005, four Tri-Max30TM extinguishers were staged on the facility.

Tri-Max30TM units were stored on the hangar ramp in the paved area surrounding the main hangar 

and leading to the helicopter parking apron. No AFFF was expended during inspections, and 

AFFF was never stored in bulk at the facility. 
Site Inspection Report

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 7-2

PFOA, PFOS, PFHxS, PFNA, and PFBS were detected in surface soil at AOI 1. Site workers, 

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

ingestion and inhalation of dust. Therefore, the exposure pathways for site workers, future 

construction workers, and trespassers are potentially complete. Additionally, PFOA, PFOS, 

PFHxS, PFNA, and PFBS were detected in the shallow subsurface soil. Future construction 

workers could contact constituents in the shallow subsurface soil via incidental ingestion; 

therefore, the exposure pathway is potentially complete. The CSM for AOI 1 is presented on 

Figure 7-1. 

7.2 Groundwater Exposure Pathway

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

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

7.2.1 AOI 1 

PFOA, PFOS, PFHxS, and/ or PFNAexceeded the SLs in three temporary monitoring wells. While 

there are no known public water supply wells downgradient of the facility, multiple wells of 

unknown use exist within 0.5 mile of the facility and are over 100 feet deep. Therefore, the 

ingestion exposure pathway to offsite residents is considered potentially complete. AASF #1 and 

the City of Decatur source most of their potable water from Lake Decatur. Therefore, the ingestion 

exposure pathway for site workers is considered incomplete. Depths to water measured in 

October 2021 during the SI ranged from 1.98 to 5.93 feet bgs. Therefore, shallow groundwater 

may be encountered during future construction activities, and the ingestion exposure pathway for 

future construction workers is considered potentially complete. Where groundwater is within 2 

feet of the surface, the incidental ingestion exposure pathway for the site worker is also potentially 

complete. Additionally, shallow groundwater may discharge to downgradient surface water 

bodies, which is further discussed in Section 7.3. The CSM for AOI 1 is presented on Figure 7-

1. 

7.3 Surface Water and Sediment Exposure Pathway

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

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

between the source and potential receptors.

7.3.1 AOI 1 

Surface water runoff from the AOI flows west and collects in a north-south drainage ditch along 

the facility’s western boundary. This drainage ditch and other surface drainages eventually flow 

toward Lake Decatur. Because PFOA, PFOS, PFHxS, PFNA, and PFBS were detected in surface 

soil, the surface water and sediment ingestion exposure pathways are potentially complete for 

site workers and future construction workers working in the ditch. Shallow groundwater may 

discharge to surface water bodies west of AASF #1, including small ponds and a stream located 

on the golf course and Lake Decatur (Figure 2-5). Because PFOA, PFOS, PFHxS, PFNA, and 

PFBS were detected in shallow groundwater at AOI 1, it is possible that those compounds may 

have migrated from groundwater to Lake Decatur and other nearby surface water bodies. 

Therefore, surface water and sediment ingestion pathway for offsite recreational users of these 

surface water bodies may be potentially complete. Drinking water at the facility and for the City of 

Decatur is sourced from Lake Decatur; therefore, the surface water ingestion exposure pathway 

for site workers and offsite residents is considered potentially complete. The CSM for AOI 1 is 

presented on Figure 7-1.
Media

SOURCE PATHWAY RECEPTOR

AOI 1 Surface Soil

Human

Activities

Precipitation/

Run-Off

Leaching/

Infiltration

Airborne Soil

particulate

Surface Soil

Surface

Water/

sediment

Subsurface

Soil

Shallow

Groundwater

Source Release

Mechanism Media Transportand Migration Media ExposureRoutes

Inhalation of

Dust

Ingestion

Ingestion

Ingestion

Ingestion

Human Receptors:

Current/ Future

Flow-Chart Continues

Partial / Possible Flow

Flow-Chart Stops

Incomplete Pathway

Potentially Complete Pathway

Potentially Complete Pathway

with Exceedance of SL

/ / / /

/ / / /

LEGEND

/ / / /

/ / /

/

Figure 7-1

Conceptual Site Model, AOI 1

Army Aviation Support Facility #1, Decatur, Illinois

Potential

Off-Facility

Source Not

under

Control of

ARNG

NOTES

1. The resident and recreational users

refer to off-facility receptors.

2. No active construction was occurring

within AOI 1 as of the date of SI field work.

Site

Worker

Construction

Worker2 Resident1

Trespasser/

Recreational

User1

Site

Worker

Construction

Worker2 Resident1 Trespasser/

Recreational

User1

/

AFFF Storage

on Hangar

Ramp Area

/ / /

AECOM 7-3
Site Inspection Report

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 7-4

THIS PAGE INTENTIONALLY BLANK
Site Inspection Report

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 8-1

8. Summary and Outcome

This section summarizes SI activities and findings. The most significant findings are summarized 

in this section and are reproduced directly or abstracted from information contained in this report. 

The outcome provides general and comparative interpretations of the findings relative to the SLs.

8.1 SI Activities

The SI field activities consisted of utility clearance, sonic soil boring, soil sample collection, 

temporary monitoring well installation and subsequent abandonment, grab groundwater sample 

collection, and land surveying. Utility clearance was performed on 21 October 2022 and all other 

field activities were conducted from 25 to 28 October 2021, in accordance with the SI QAPP 

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

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

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

Table B-15 as follows. 

• Eleven (11) soil samples from six boring locations; 

• Six grab groundwater samples from six temporary wells; 

• Thirteen (13) QA/QC samples.

An SI is conducted when the PA determines an AOI exists based on probable use, storage, and/or 

disposal of PFAS-containing materials. The SI includes multi-media sampling at the AOI to 

determine whether or not a release has occurred. The SI may conclude further investigation is 

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

required. Additionally, the CSM was refined to assess whether a potentially complete pathway 

exists between the source and potential receptors for potential exposure at the AOI, which are 

described in Section 7.

8.2 Outcome 

Based on the results of this SI, further evaluation under CERCLA is warranted in an RI for AOI 1. 

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

to drinking water receptors from AOI 1 from sources on the facility resulting from historical DoD 

activities. Sample analytical concentrations collected during the SI were compared to the project

SLs in soil and groundwater, as described in Table 6-1. A summary of the results of the SI data 

relative to the SLs is as follows:

• At AOI 1:

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

below their SLs. 

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

exceeded the SL of 6 ng/L, with a maximum concentration of 19.2 ng/L at location 

AOI01-01. PFOS exceeded the SL of 4 ng/L, with a maximum concentration of 86.6

ng/L at location AOI01-04. PFHxS exceeded the SL of 39 ng/L, with a maximum 

concentration of 69.6 ng/L at location AOI01-04. Lastly, PFNA exceeded the SL of 6 

ng/L, with a maximum concentration of 6.33 ng/L at AOI01-04 Based on the results 

of the SI, further evaluation of AOI 1 is warranted in an RI.
Site Inspection Report

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 8-2

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

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

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

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

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

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

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

Table 8-1 summarizes the SI results for soil and groundwater used to determine if an AOI should 

be considered for further investigation under CERCLA and undergo an RI. 

Table 8-1: Summary of Site Inspection Findings and Recommendations

AOI Potential 

Release Area

Soil –

Source 

Area

Groundwater – 

Source Area

Future 

Action

1 Hangar Ramp Proceed 

to RI 

Legend:

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected
Site Inspection Report

Army Aviation Support Facility #1, Decatur, Illinois

AECOM 9-1

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