Final

Site Inspection Report

Duncan Readiness Center and Army Aviation Support 

Facility 

New Castle, Delaware

Per- and Polyfluoroalkyl Substances Impacted Sites

ARNG Installations, Nationwide

March 2022

Prepared for

Army National Guard Headquarters 

111 S. George Mason Drive 

Arlington, VA 22204

UNCLASSIFIED 

Contract No. W912DR-19-D-0005
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EA Project No. 634250383 i 

TABLE OF CONTENTS

APPENDICES .............................................................................................................................. iii

LIST OF FIGURES ..................................................................................................................... iv

LIST OF TABLES ....................................................................................................................... iv

LIST OF ACRONYMS AND ABBREVIATIONS .................................................................... v

EXECUTIVE SUMMARY .......................................................................................................... 1

1. INTRODUCTION.......................................................................................................... 1-1

1.1 PROJECT AUTHORIZATION ........................................................................... 1-1

1.2 SI PURPOSE ....................................................................................................... 1-1

2. SITE BACKGROUND .................................................................................................. 2-1

2.1 FACILITY LOCATION AND DESCRIPTION ................................................. 2-1

2.2 FACILITY ENVIRONMENTAL SETTING ...................................................... 2-1

2.2.1 Soils...........................................................................................................2-1

2.2.2 Geology .................................................................................................... 2-1

2.2.3 Hydrogeology .......................................................................................... 2-2

2.2.4 Hydrology ................................................................................................ 2-3

2.2.5 Climate ..................................................................................................... 2-4

2.2.6 Current and Future Land Use ................................................................... 2-4

2.2.7 Critical Habitat and Threatened/Endangered Species .............................. 2-4

2.3 HISTORY OF AQUEOUS FILM FORMING FOAM USE ............................... 2-5

3. SUMMARY OF AREAS OF INTEREST ................................................................... 3-1

3.1 AOI 1 ................................................................................................................... 3-1

3.1.1 Helicopter Crash Site ............................................................................... 3-1

3.2 AOI 2 ................................................................................................................... 3-1

3.2.1 Hangar ...................................................................................................... 3-1

3.3 ADJACENT SOURCES ...................................................................................... 3-2

3.3.1 Delaware Auto Salvage Fire .................................................................... 3-2

3.3.2 Delaware State Fire School ...................................................................... 3-2

3.3.3 Aircraft Crash Site ................................................................................... 3-2

3.3.4 DANG Fire Training Area ....................................................................... 3-2

3.3.5 Airplane Crash Site .................................................................................. 3-2

3.3.6 New Castle Air National Guard Base ...................................................... 3-3

4. PROJECT DATA QUALITY OBJECTIVES............................................................. 4-1

4.1 PROBLEM STATEMENT .................................................................................. 4-1

4.2 GOALS OF THE STUDY ................................................................................... 4-2

4.3 INFORMATION INPUTS ................................................................................... 4-2

4.4 STUDY BOUNDARIES ..................................................................................... 4-3
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4.5 ANALYTICAL APPROACH ............................................................................. 4-3

4.6 DATA USABILITY ASSESSMENT .................................................................. 4-4

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

4.6.2 Accuracy .................................................................................................. 4-5

4.6.3 Representativeness ................................................................................... 4-6

4.6.4 Comparability .......................................................................................... 4-6

4.6.5 Completeness ........................................................................................... 4-7

4.6.6 Sensitivity ................................................................................................ 4-7

4.6.7 Data Usability Summary .......................................................................... 4-7

5. SITE INSPECTION ACTIVITIES .............................................................................. 5-1

5.1 PRE-INVESTIGATION ACTIVITIES ............................................................... 5-2

5.1.1 Technical Project Planning ...................................................................... 5-2

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

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

5.2 SOIL BORINGS AND SOIL SAMPLING ......................................................... 5-2

5.3 TEMPORARY WELL INSTALLATION AND GROUNDWATER GRAB 

SAMPLING ......................................................................................................... 5-4

5.4 EXISTING MONITORING WELL GROUNDWATER GRAB SAMPLING .. 5-4

5.5 SYNOPTIC WATER LEVEL MEASUREMENTS ........................................... 5-4

5.6 SURVEYING ...................................................................................................... 5-5

5.7 INVESTIGATION-DERIVED WASTE ............................................................. 5-5

5.8 LABORATORY ANALYTICAL METHODS ................................................... 5-5

5.9 DEVIATIONS FROM UFP-QAPP ADDENDUM ............................................. 5-6

6. SITE INSPECTION RESULTS ................................................................................... 6-1

6.1 SCREENING LEVELS ....................................................................................... 6-1

6.2 SOIL PHYSICOCHEMICAL ANALYSES ........................................................ 6-1

6.3 AOI 1 – HELICOPTER CRASH SITE ............................................................... 6-2

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

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

6.3.3 Conclusions .............................................................................................. 6-3

6.4 AOI 2 – HANGAR .............................................................................................. 6-3

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

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

6.4.3 Conclusions .............................................................................................. 6-4

6.5 BOUNDARY SAMPLE LOCATIONS .............................................................. 6-4

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

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

6.5.3 Conclusions .............................................................................................. 6-5

7. EXPOSURE PATHWAYS ............................................................................................ 7-1

7.1 SOIL EXPOSURE PATHWAY .......................................................................... 7-1

7.1.1 AOI 1 – Helicopter Crash Site ................................................................. 7-1
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7.1.2 AOI 2 – Hangar ........................................................................................ 7-2

7.2 GROUNDWATER EXPOSURE PATHWAY.................................................... 7-2

7.2.1 AOI 1 – Helicopter Crash Site ................................................................. 7-2

7.2.2 AOI 2 – Hangar ........................................................................................ 7-2

7.3 SURFACE WATER AND SEDIMENT EXPOSURE PATHWAY ................... 7-3

8. SUMMARY AND OUTCOME .................................................................................... 8-1

8.1 SI ACTIVITIES SUMMARY ............................................................................. 8-1

8.2 SI GOALS EVALUATION ................................................................................. 8-1

8.3 OUTCOME .......................................................................................................... 8-2

9. REFERENCES ............................................................................................................... 9-1

APPENDICES

Appendix A Data Validation Reports

Appendix B Field Documentation

B1. Log of Daily Notice of Field Activities

B2. Sampling Forms 

B3. Survey Data 

Appendix C Photographic Log 

Appendix D TPP Meeting Minutes

Appendix E Boring Logs and Well Construction Diagrams 

Appendix F Analytical Results

Appendix G Laboratory Reports
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LIST OF FIGURES

Number Title

2-1 Facility Location

2-2 Facility Topography 

2-3 Groundwater Features

2-4 Surface Water Features

2-5 Groundwater Elevations 

3-1 Areas of Interest

5-1 Site Inspection Sample Locations

6-1 PFOS Detections in Soil (AOI 1 and AOI 2)

6-2 PFOA Detections in Soil (AOI 1 and AOI 2)

6-3 PFBS Detections in Soil (AOI 1 and AOI 2) 

6-4 PFOS, PFOA, and PFBS Detections in Groundwater (AOI 1 and AOI 2)

7-1 Conceptual Site Model, AOI 1 

7-2 Conceptual Site Model, AOI 2

LIST OF TABLES

Number Title

ES-1 Screening Levels (Soil and Groundwater) 

ES-2 Summary of Site Inspection Findings 

ES-3 Site Inspection Recommendations 

5-1 Samples by Medium, Duncan RC and AASF, New Castle, Delaware, Site 

Inspection Report 

5-2 Soil Boring Depths and Temporary Well Screen Intervals, Duncan RC and AASF, 

New Castle, Delaware, Site Inspection Report 

5-3 Groundwater Elevation, Duncan RC and AASF, New Castle, Delaware, Site 

Inspection Report 

6-1 Screening Levels (Soil and Groundwater) 

6-2 PFAS Detections in Surface Soil, Site Inspection Report, Duncan RC and AASF 

6-3 PFAS Detections in Shallow Subsurface Soil, Site Inspection Report, Duncan RC 

and AASF

6-4 PFAS Detections in Groundwater, Site Inspection Report, Duncan RC and AASF 

8-1 Summary of Site Inspection Findings 

8-2 Site Inspection Recommendations 
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LIST OF ACRONYMS AND ABBREVIATIONS

°C Degrees Celsius

% Percent

μg/kg Microgram(s) per kilogram

μg/L Microgram(s) per liter

AASF Army Aviation Support Facility 

AECOM AECOM Technical Services, Inc. 

AFFF Aqueous Film Forming Foam

amsl Above mean sea level

ANG Air National Guard

AOI Area of Interest

ARNG Army National Guard

bgs Below ground surface

bmsl Below mean sea level

btoc Below top of casing

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

CSM Conceptual site model

DA Department of the Army

DANG Delaware Air National Guard

DNREC Delaware Department of Natural Resources and Environmental Control

DEARNG Delaware Army National Guard 

DoD Department of Defense

DPT Direct-push technology

DQI Data Quality Indicator

DQO Data Quality Objectives

EA EA Engineering, Science, and Technology, Inc., PBC

EIS Extraction internal standards

ELAP Environmental Laboratory Accreditation Program

EM Engineer Manual

EB Equipment Blank 

FB Field blank

ft Foot (feet)

HA Health Advisory

HDPE High-density polyethylene

HQ Hazard Quotient

IDW Investigation-derived waste

ITRC Interstate Technology Regulatory Council
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LC/MS/MS Liquid Chromatography Tandem Mass Spectrometry

LCS Laboratory control sample 

LCSD Laboratory control sample duplicate

LOQ Limit of quantification

MS Matrix spike

MSD Matrix spike duplicate

NCANGB New Castle Air National Guard Base

NELAP National Environmental Laboratory Accreditation Program 

NEtFOSAA N-ethylperfluorooctane sulfonamidoacetic acid 

ng/L Nanogram(s) per liter

NMeFOSAA N-methylperfluorooctane sulfonamidoacetic acid

No. Number

OSD Office of the Secretary of Defense

PA Preliminary Assessment

PFAS Per- and polyfluoroalkyl substances

PFBS Perfluorobutanesulfonic acid

PFOA Perfluorooctanoic acid

PFOS Perfluorooctanesulfonic acid

PVC Polyvinyl chloride

QAPP Quality Assurance Project Plan

QC Quality Control

QSM Quality Systems Manual

RI Remedial Investigation 

RPD Relative percent difference

SI Site Inspection

SL Screening level

TCRA Time Critical Removal Action

TOC Total organic carbon

TPP Technical Project Planning

UCMR3 Unregulated Contaminant Monitoring Rule 3

UFP Uniform Federal Policy 

USACE U.S. Army Corps of Engineers

USEPA U.S. Environmental Protection Agency
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EXECUTIVE SUMMARY

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

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

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

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

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

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

completed at the Duncan Readiness Center (RC) and Army Aviation Support Facility (AASF). 

The Duncan RC and AASF is also referred to as the “facility” throughout this document. 

The facility, operated by the Delaware ARNG (DEARNG), encompasses approximately 

17.3 acres in New Castle, Delaware. The facility is located adjacent to the New Castle Airport, 

approximately 5.6 miles southwest of the City of Wilmington. Delaware’s Air National Guard 

base is located across airport taxiways to the northeast. The Duncan RC and AASF lies within 

the Coastal Plain region of Delaware, which is composed of variegated silts and clays. DEARNG 

leased the property from the New Castle Airport in 1973 for a 50-year term and has been used as 

an active military facility since. The Duncan RC and AASF is currently, and has been 

historically, used for aircraft maintenance and administrative purposes. The facility includes an 

aircraft hangar, administrative offices, and helicopter landing pads. 

The PA Report (AECOM Technical Services, Inc. 2020) identified one potential PFAS release 

area at the facility, the 1970s Helicopter Crash Site. Additionally, during SI scoping meetings 

with the ARNG, the Hangar was determined to be a potential PFAS release area. The release 

areas were grouped into two AOIs: AOI 1, which includes the Helicopter Crash Site, and AOI 2, 

which includes the Hangar. The SI field activities were conducted from 2 to 3 June 2021 and 

included the collection of soil and groundwater samples. 

To fulfill the project Data Quality Objectives set forth in the approved installation-specific

Uniform Federal Policy – Quality Assurance Project Plan Addendum (EA 2021b), samples were 

collected and analyzed for a subset of 24 PFAS via liquid chromatography with tandem mass 

spectrometry (LC/MS/MS) compliant with Quality Systems Manual Version 5.3 Table B-15. 

The 24 PFAS analyzed as part of the ARNG SI program are specified in Section 5.8 of this SI 

Report. 

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

Environmental Response, Compensation, and Liability Act (CERCLA) process based on riskbased SLs for soil and groundwater, as described in a memorandum from the Office of the 

Secretary of Defense dated 15 September 2021 (Deputy Assistant Secretary of Defense 2021). 

The ARNG PFAS SIs follow this DoD policy and, should the maximum site concentration for 

sampled media exceeds the SLs established in the OSD memorandum, the AOI will proceed to 

the next phase under CERCLA. The SLs apply to three compounds, PFOA, PFOS, and PFBS, 

for both soil and groundwater, as presented in Table ES-1. All other results presented in this 

report are considered informational in nature and serve as an indication as to whether soil and

groundwater within the boundaries of the facility may be impacted with other PFAS analytes.
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Chemical concentrations from samples were compared against the project SLs as described in 

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

• AOI 1 − PFOS or PFOA were detected in groundwater at concentrations exceeding the 

individual SLs of 40 nanograms per liter (ng/L) in all temporary well locations associated 

with AOI 1, with maximum concentrations of PFOS at 150 ng/L and PFOA at 120 ng/L

at locations AOI01-02 and AOI01-01, respectively. PFBS was detected in groundwater at 

AOI 1, but did not exceed the SL.

• AOI 2 − PFOA, PFOS, and PFBS were detected in groundwater at AOI 2. PFOA 

exceeded the SL in groundwater with a concentration of 230 ng/L at AOI02-01. PFOS

and PFBS did not exceed the SLs. 

• AOI 1 and 2 − PFOA and PFOS were detected in soil at both AOI 1 and 2 at low 

concentrations, several orders of magnitude below the SLs. There were no detections of 

PFBS at either AOI. 

• Upgradient Boundary Samples − PFOA, PFOS, and PFBS were detected in groundwater 

upgradient of AOI 1 and AOI 2 in samples taken from locations DAASF-01 and DAASF02. The sample taken from location DAASF-02 exceeded the PFOA SL with a 

concentration of 150 ng/L, but there were no exceedances in the sample taken from 

location DAASF-01. The sample taken from location DAASF-03, located along the 

northeastern facility boundary, also exceeded the SL for PFOA with a concentration of 

280 ng/L.

• Downgradient Boundary Samples - PFOA was detected in groundwater at downgradient 

location MW-15 with a concentration of 100 ng/L, exceeding the SL. PFBS and PFOS 

were detected at this location below their respective SLs. 

• Recommendations − Based on the results of the SI, further evaluation of AOIs 1 and 2

are warranted in a Remedial Investigation.

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

models which were updated with the SI findings, there is potential for exposure to residential 

drinking water receptors caused by potential DoD activities at the facility as well as potential and 

known off-facility adjacent sources.

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

further investigation under CERCLA and undergo an RI. Based on the results of this SI, further 

evaluation is warranted in the RI for AOI 1: Helicopter Crash Site and AOI 2: Hangar.
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Table ES-1 Screening Levels (Soil and Groundwater)

Analyte

Residential

(Soil)

(μg/kg) 1

Industrial / Commercial

Composite Worker

(Soil)

(μg/kg) 1

Tap Water

(Groundwater)

(ng/L) 1

PFOA 130 1,600 40

PFOS 130 1,600 40

PFBS 1,900 25,000 600

Notes:

1. Deputy Assistant Secretary of Defense. 2021. Risk Based Screening Levels Calculated for 

PFOS, PFOA, PFBS in Groundwater and Soil using United States Environmental Protection 

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

15 September 2021. 

μg/kg = Microgram(s) per kilogram.

ng/L = Nanograms(s) per liter.

Table ES-2 Summary of Site Inspection Findings

AOI Potential PFAS Release Area

Soil –

Source Area

Groundwater –

Source Area

Groundwater –

Facility Boundary

1 Helicopter Crash Site

2 Hangar

Legend:

 = Detected; exceedance of screening levels.

 = Detected; no exceedance of screening levels.

 = Not detected.

Table ES-3. Site Inspection Recommendations

AOI Description Rationale Future Action

1 Helicopter Crash Site Exceedances of the SLs in 

groundwater at source area. No 

exceedances of SLs in soil.

Proceed to RI

2 Hangar Exceedances of SLs in groundwater 

at source area. No exceedances of 

SLs in soil.

Proceed to RI
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1. INTRODUCTION

1.1 PROJECT AUTHORIZATION

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

Assessments (PAs) and Site Inspections (SIs) for Per- and Polyfluoroalkyl Substances (PFAS)-

impacted sites at ARNG facilities nationwide. This work is supported by the U.S. Army Corps of 

Engineers (USACE) Baltimore District and their contractor, EA Engineering, Science, and 

Technology, Inc., PBC, (EA) under Contract Number (No.) W912DR-19-D-0005, Task Order 

No. W912DR20F0383. The ARNG performed this SI at the Duncan Readiness Center (RC) and 

Army Aviation Support Facility (AASF) (also referred to as the “facility”) in Delaware. 

The SI project elements were performed by EA in accordance with the Comprehensive

Environmental Response, Compensation, and Liability Act (CERCLA) (U.S. 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 Army requirements and guidance for field investigations, including specific

requirements for sampling for perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid 

(PFOS), perfluorobutanesulfonic acid (PFBS), and the group of related compounds known in the 

industry as PFAS. The term PFAS will be used throughout this plan to encompass all PFAS 

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

the suspected releases being evaluated, along with the other 21 related compounds listed in the 

task order. 

1.2 SI PURPOSE

A PA was performed at the facility (AECOM Technical Services, Inc. [AECOM] 2020) that 

identified a single potential PFAS release area, which was grouped into one Area of Interest 

(AOI). The SI was performed as the next step in the CERCLA process. During the SI scoping 

process a second AOI was identified. The objective of the SI was to identify whether there has 

been a release to the environment from the AOIs and determine the presence or absence of 

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

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

SI has five goals:

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

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

2) Determine the potential need for a removal action (i.e., Time Critical Removal Action

[TCRA]; applies to drinking water only).

3) Collect or develop data to evaluate the release.

4) Collect additional data to develop the conceptual site model (CSM) in preparation for an

effective remedial investigation (RI).
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5) Collect data to determine whether the release is more than likely the result of activities 

associated with the Department of Defense (DoD).

In addition to the USEPA identified goals of an SI, the ARNG SI effort also identifies whether 

there are any impacts from potential off-facility PFAS sources. 
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2. SITE BACKGROUND

2.1 FACILITY LOCATION AND DESCRIPTION

The facility occupies 17.3 acres in New Castle, Delaware, adjacent to the New Castle Airport. 

Wilmington, Delaware, located 5.6 miles from the facility, is the nearest metropolitan area. 

Delaware’s Air National Guard (DANG) base is located across the airport taxiways to the 

northeast. The surrounding properties are primarily zoned for single-family homes and 

businesses. 

The facility property and the present day Wilmington Airport was an active duty Air Force Base 

in the 1940s. In 1949, the War Department started parceling the property. In 1973, the State of 

Delaware issued the DEARNG a certificate of title for the portion of the property containing the 

AASF and Duncan RC, and has since been used as an active military facility. The facility is 

comprised of an aircraft hangar to house machinery, several administrative offices, and 

helicopter landing pads. The AASF houses the maintenance hangar and the Duncan RC houses 

the administrative offices. Airport runways and taxiways are located directly adjacent to the 

facility, which is protected by a guarded gate (AECOM 2020). The facility location and layout 

are shown on Figure 2-1. 

2.2 FACILITY ENVIRONMENTAL SETTING

Located in northern New Castle County, Delaware, southwest of Wilmington, Delaware, the 

facility is approximately 64 feet (ft) above mean sea level (amsl). The Christina River, located 

north of the facility, is part of the Christina River Basin reaching into Pennsylvania and 

Maryland and flows generally northeast into the Delaware River. The Delaware River, located 

east of the facility, flows south until it merges into the Delaware Bay. Ground surface within the 

facility is predominantly covered by buildings, asphalt, and concrete; however, green space 

exists around the parking lot and on the southwestern corner of the property, surrounding the 

stormwater detention basin. The facility lies within the Coastal Plain region of Delaware, which 

is composed of variegated silts and clays and is a predominantly low, flat area about 100 ft amsl

(AECOM 2020).

The following sections include information on geology, hydrogeology, hydrology, climate, and 

current and future land use. The facility topography at Duncan RC and AASF are shown on 

Figure 2-2. The regional geology and groundwater features are shown on Figure 2-3. The 

regional surface water features and drainage basins are shown on Figure 2-4. Groundwater 

elevations and contours are presented on Figure 2-5. 

2.2.1 Geology 

The facility lies within the northern edge of the Atlantic Coastal Plain Province, which consists 

of semi- and unconsolidated fluvial deposited sediments. The Columbia Formation, middle 

Pliestocene in age, overlies the older Cretaceous Potomac Formation at the facility, dipping to 

the east. These formations were deposited in non-marine, fluvial environments (EA 2019). 
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The Columbia formation is characterized by fine to coarse, feldspathic quartz sand with varying 

amounts of gravel and scattered beds of tan to reddish-gray clayey silt. The Columbia Formation 

in New Castle County ranges in thickness from less than 10 ft to over 130 ft, where it occurs in 

channel deposits. 

Eroded surfaces within the underlying Potomac Formation are filled by sediments of the 

Columbia Formation, forming paleo-channels that trend northeast to southwest with a thickness 

of approximately 70 ft. A paleo-channel is located adjacent to the New Castle Airport to the east. 

The Potomac Formation consists of interbedded dark-red, gray, pink, and white silty clay to 

clayey silt and fine to medium sand. Underlying the Potomac Formation is the Lower Paleozoic 

Wilmington Complex, consisting of felsic and mafic gneiss and minor schist, as well as the 

Brandywine Blue Gneiss, consisting of granulite facies felsic gneisses (EA 2019). 

Soils encountered during the SI consisted mainly of silts, sands, some gravel, and minor clay 

lenses. Bedrock was not encountered during drilling.

2.2.2 Hydrogeology

New Castle County, Delaware, has two aquifers: the Columbia and Potomac. The Columbia is

the surficial aquifer in this area and can either be perched or act as a hydrologic unit with the

Potomac aquifer. A previous investigation was conducted by the ANG approximately 1 mile

from the facility. At the time of the PA, it was inferred that the geologic information provided in 

this investigation was similar to that at the facility due to its proximity. The study indicated that

the Columbia Formation in this area is predominantly dry, with perched water tables present. The 

Potomac aquifer consists of two independent (Upper and Middle), laterally continuous sand 

bodies within the water-bearing zones of the Potomac Formation. The water table under normal 

conditions sits at an elevation of approximately 20 to 30 ft amsl (AECOM 2020). During the SI, 

depth to water ranged from 25.88 to 32.89 ft (Figure 2-5). 

The Upper Potomac aquifer lies in both the shallow and intermediate groundwater-bearing

zones. The shallow zone extends from 0 to 30 ft amsl, and there is no clear distinction between

the surficial Columbia aquifer and the Upper Potomac aquifer. Separated from the shallow zone

by a semi-confining layer of clay, the intermediate groundwater-bearing zone ranges from 1 to

20 ft thick, extends approximately 50 ft below mean sea level (bmsl), and is considered to be

part of the Upper Potomac aquifer. Results of groundwater elevation data from a previous

investigation at the adjacent ANG facility suggest that the shallow and intermediate zones are

interconnected, as they show similar trends in groundwater levels and flow directions (Amec

Foster Wheeler 2019). Groundwater elevations calculated using depth to groundwater 

measurements and survey data collected during the SI indicated groundwater within the shallow 

and intermediate aquifer underlying the southern and western portions of the facility flows 

primarily to the north/northeast and to the northwest in the eastern portion of the facility.

The Middle Potomac aquifer is considered the deep groundwater-bearing zone and is separated

from the Upper Potomac aquifer by a layer of clay 60 to 80 ft thick; it does not vertically

transmit water. Below the clay layer, the aquifer’s water-bearing sands extend from 120 to 130 ft 

bmsl. Groundwater levels are about 5 to 10 ft bmsl, suggesting that the groundwater is
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confined, and there is little transmission of water vertically between the Upper and Middle 

Potomac aquifers. Groundwater in the Middle Potomac aquifer flows to the south-southeast

(AECOM 2020).

In New Castle County, south of the Chesapeake and Delaware Canal, approximately 10 miles

south of the facility, nearly all drinking water is from groundwater provided by public and

private wells. However, north of the canal in northern New Castle County, where the facility is

located, groundwater supplies only 30 percent (%) of drinking water (AECOM 2020).

Based on the USEPA Unregulated Contaminant Monitoring Rule 3 (UCMR3) data, it was

indicated during the PA that PFAS were detected in a public water system above the Health 

Advisory (HA) within 20 miles of the facility between 2013 and 2015. In May 2016, USEPA 

replaced provisional HAs with a more conservative HA of 70 parts per trillion for PFOS and 

PFOA, individually or combined. PFAS analyses performed prior to 2016 had method detection 

limits that were higher than currently achievable. Thus, it is possible that low concentrations of 

PFAS were not detected during the UCMR3 but might be detected if analyzed today. The 

Delaware Department of Natural Resources and Environmental Control (DNREC) reported that 

Artesian Water Company, a primary drinking water provider in the area, and the City of New 

Castle Municipal Services Commission detected PFAS in public water supply wells within the 

area of the facility. The area of investigation is approximately 7 square miles and is bounded to 

the north by Interstate 295, the Delaware River to the east, Route 273 to the south, and Route 13 

and New Castle Airport to the west. This area of PFAS contamination includes New Castle 

County Airport, the facility property, and surrounding residential areas. The public water supply 

is treated for PFAS contamination prior to distribution (AECOM 2020). 

EDRTM conducted a well search for a 1-mile radius surrounding the facility and it was noted that 

there are eight private domestic groundwater supply wells within 1 mile of the facility. In 

November 2016, in response to the previously described lowering of the HA levels, USEPA 

collected samples from one of these private wells located approximately 1 mile northwest of 

Duncan RC and AASF. While PFOS was not detected in any collected samples, PFOA was 

detected in exceedance of the HA. Attempts were made by DNREC and USEPA to further 

investigate the well, however, the owner did not respond (USEPA 2018a). 

Using additional online resources, such as state and local geographic information system

databases, wells were researched to a 4-mile radius of the facility. According to data from the 

state of Delaware, the majority of wells to the southeast of the facility, deep groundwater’s 

downgradient direction, are monitoring wells. A 2019 USEPA report figure shows four Artesian 

public water supply wells located 3 miles south of the facility. However, according to interviews 

with DNREC, there are additional Artesian and City of New Castle Municipal Service 

Commission public wells located within 3 miles of the facility to the northeast, east, and 

southeast. North of the facility, shallow groundwater’s downgradient direction to the Christina 

River, there are a combination of monitoring and domestic groundwater wells (AECOM 2020).

2.2.3 Hydrology

North of the facility is the Christina River, a part of the Christina River Basin that extends from

Pennsylvania through New Castle County, Delaware. The Christina River Basin is characterized
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by dendritic interconnected rivers, streams, and wetlands, with outflow to the Delaware River.

The Christina River is in the southernmost area of the basin and flows northeast, into the

Delaware River. Surface water accounts for 70% of New Castle County’s water supply, the

majority of which comes from the Christina River Basin, which provides 60% of New Castle

County’s water overall. The majority of the Christina River is in New Castle County, with

headwaters in Maryland. The Christina River is tidal from just south of the town of Christiana to

its convergence with the Delaware River. This section of the Christina lies approximately 1 mile

west of the facility and tidal freshwater wetlands occur throughout the area (AECOM 2020).

The facility sits on the Lower Christina River Watershed, at the edge of the Christina Basin, with

wetlands lying north of the facility. On facility grounds, runoff flows away from the paved areas

and structures into a detention basin on the southern end of the property, where runoff will

infiltrate or evaporate. However, surrounding the facility, general surface water flow is north into

the Christina River and Nonesuch Creek, which converge downstream and continue northeast to

the Delaware River (AECOM 2020).

The facility is closest to the 68-mile marker of the Delaware River. A presentation from the

Delaware River Basin Commission provides 2009 PFAS concentration data for media tested

along the Delaware River. PFAS were detected in surface water in the section closest to the

facility, between river miles 68 and 70. The 2009 PFOA concentration at river mile 68.1 was

0.0277 micrograms per liter (μg/L), and the PFOS concentration was 0.00575 μg/L (AECOM

2020).

2.2.4 Climate

The climate at the facility is humid continental. The Delaware Bay and Atlantic Ocean to the east

and south, and the Chesapeake Bay to the west moderate temperature extremes in the winter and

summer months. Although the extremes are lessened, the climate at the facility is still continental

with hot summers, cold winters, and precipitation throughout the year. Mean annual temperature

in New Castle is 54 degrees Fahrenheit (°F). Average annual high temperature for Wilmington,

Delaware, in New Castle County, is 64.1 °F and average annual low temperature is 45.8 °F.

Annual precipitation for Wilmington is approximately 43 inches of rain and 19 inches of

snowfall (AECOM 2020).

2.2.5 Current and Future Land Use

The facility currently resides on a portion of land leased from the New Castle Airport under the

terms of a 50-year lease. It has been an active military facility since the signing of the lease in

December 1973. The facility is currently used for aircraft maintenance and administrative

activities. Future land use is not anticipated to change (AECOM 2020).

2.2.6 Critical Habitat and Threatened/Endangered Species

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

species in New Castle, Delaware (U.S. Fish and Wildlife Service 2021):

• Birds: Eastern Black Rail, Laterallus jamaicensis ssp. jamaicensis (Threatened)
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• Reptiles: Bog Turtle, Clemmys muhlenbergii (Threatened)

• Flowering Plants: Small Whorled Pogonia, Isotria medeoloides (Threatened); and Swamp 

Pink, Helonias bullata (Threatened)

• Mammals: Northern Long-eared Bat, Myotis septentrionalis (Threatened).

2.3 HISTORY OF AQUEOUS FILM FORMING FOAM USE

Aqueous film forming foam (AFFF), a firefighting agent, was commonly used by the U.S.

military to extinguish petroleum fires, for firefighting training, and for the suppression of fires in 

uncontained areas. Military use of AFFF began in the 1970s and was most widely used at DoD 

installations with airfields. Two Potential PFAS release areas were identified at the Duncan RC 

and AASF. The first AOI was identified where AFFF-containing firefighting foam may have 

been released onsite at the Duncan RC and AASF by the municipal fire department when they 

responded to a helicopter crash that occurred at the site boundary in the 1970s. Interviews and 

records obtained during the PA indicate that the facility’s hangar fire suppression system has 

contained JET-X since a 2011 retrofitting. This synthetic foam concentrate is intended for 

firefighting applications but it is unknown if it is PFAS-containing. There is also uncertainty as 

to what type of foam was contained in the fire suppression system prior to the 2011 retrofitting. 

As such, the SI included the hangar as a potential AOI for investigation. A more detailed 

description of each AOI is presented in Chapter 3. 
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3. SUMMARY OF AREAS OF INTEREST

Based on the PA findings, one AOI was identified at the Duncan RC and AASF: AOI 1 

Helicopter Crash Site. A second AOI was identified at the facility during scoping for the SI: 

AOI 2 Hangar. Additionally, several adjacent potential sources of PFAS have been identified 

(Figure 3-1). A summary of the AOIs and the adjacent potential sources is presented below. 

3.1 AOI 1 

3.1.1 Helicopter Crash Site

The ARNG Helicopter Crash Site is located on the southeastern boundary between the facility 

and the New Castle Airport properties. The crash occurred sometime in the 1970s. Historical 

knowledge suggests the municipal fire department responded to the scene using a foam fire 

suppressant; however, it is unknown if the foam contained AFFF. The municipal fire department 

is known to use AFFF to extinguish fires. The released foam likely followed onsite surface water 

pathways towards the southwestern portion of the facility, where runoff collects in a detention 

basin until it evaporates or infiltrates to the subsurface. The facility layout has been reconstructed 

since the time of the crash, and the suspected crash area is now mostly covered by an impervious 

concrete surface (AECOM 2020). 

3.2 AOI 2 

3.2.1 Hangar

The hangar has been an active military facility since the signing of the property lease in 

December 1973. Based on a review of historical aerial photographs, the site was initially 

developed to include a hangar; however, no information regarding the previous fire suppression 

system associated with the original hangar was found. According to interviewees, at the 

completion of renovations of the hangar and administrative wing in 2011, the existing fire 

suppression system in the hangar was retrofitted with a Jet-X 2% high expansion foam 

concentrate system. During retrofitting, the previous system was discharged with an aqueous 

soap and water solution to test functionality before Jet-X was placed in the system. Prior to the 

installation of the Jet-X deluge system, the fire suppression system was equipped with foam 

which was suspected to be non-PFAS containing. However, interviewees could not confirm the 

foam type. The storage tank for the current deluge system is located inside the fire suppression 

equipment room, which is accessible from outside of the building. The foam deluge system, 

automatic sprinkler system, and dry pipe sprinkler system are all checked on a quarterly basis by 

Allegiant Fire Protection. A release in the hangar would follow surface water drainage pathways 

to the north, subsequently infiltrating in the surrounding grass. It is unknown if Jet X is PFAScontaining. However, there is uncertainty as to what type of foam was contained in the fire 

suppression system prior to the 2011 retrofitting. As a result, the ARNG conservatively operated 

under the potential for the historic (prior to 2011) fire suppression foam to be PFAS-containing.
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3.3 ADJACENT SOURCES

Six potential off-facility sources of PFAS are adjacent to the facility and are not under the 

control of the Delaware ARNG (DEARNG). A description of each off-facility source is 

presented below and shown on Figure 3-1. 

3.3.1 Delaware Auto Salvage Fire

A fire started in July 2018 at the Delaware Auto Savage, approximately 1.3 miles from the 

Duncan RC and AASF. An estimated 400 vehicles ignited, but it is unknown how the fire began. 

Emergency response units came from the surrounding cities in order to control the fire using 

only water, as reported by the local news agencies. There is no suspected PFAS release at this 

location attributable to the use of AFFF (AECOM 2020). The Delaware Auto Salvage Fire 

occurred downgradient and is unlikely to impact the facility. 

3.3.2 Delaware State Fire School

Firefighting training exercises are conducted approximately 0.5 mile north of the Duncan RC and 

AASF at the Delaware State Fire School New Castle. It is unknown if the foam used during these 

trainings contains AFFF. The Delaware Fire School has been identified as a potential off-facility 

source of PFAS (AECOM 2020). The Delaware State Fire School is located downgradient and is 

unlikely to impact the facility. 

3.3.3 Aircraft Crash Site

While on a test flight, a military aircraft touched the ground and ignited a small fire in 1991. The 

Delaware Air National Guard (DANG) fire department responded to this event, but it is 

unknown whether AFFF was used to extinguish the fire. Based on the prevalent use of AFFF by 

the DANG, the crash site has been identified as a potential off-facility source of PFAS (AECOM 

2020). The Aircraft Crash Site is located upgradient and has the potential to impact the facility. 

3.3.4 DANG Fire Training Area

The DANG’s current operational Fire Training Area is located approximately 80 ft southwest of 

the southwestern corner of the Duncan RC and AASF property. Training with foam has been 

reported to occur at this location, but it is unknown if the foam is AFFF-containing. The DANG 

Fire Training Area has been identified as a potential off-facility source of PFAS (AECOM 

2020). The DANG Fire Training Area is located up- and cross-gradient and has the potential to 

impact the facility.

3.3.5 Airplane Crash Site

An aircraft crashed due to malfunctioning landing gear at the adjacent ANG base in November 

of 2018. There was no fire associated with the crash, and no emergency action was taken. The 

Airplane Crash Site has no suspected PFAS release (AECOM 2020).
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3.3.6 New Castle Air National Guard Base 

In 2017, an SI was conducted at the New Castle Air National Guard Base (NCANGB), which is 

located less than a mile east and cross-gradient of Duncan RC and AASF. 

During the investigation, sampling (soil, surface water, and groundwater) was conducted to 

determine the presence/absence of PFAS at eight potential release locations and the facility 

boundary (AMEC Foster Wheeler 2019). The results of the surface and subsurface soil analysis 

indicated that PFAS was detected above the laboratory reporting limit; however, no compounds 

exceeded the screening criteria in any soil samples. Analytical results from the groundwater 

samples indicated that two compounds (PFOA and PFOS) exceeded groundwater screening 

criteria.
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4. PROJECT DATA QUALITY OBJECTIVES

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

the quality of data and define the level of certainty required to support the project decisionmaking process. The specific DQOs established for the Duncan RC and AASF are described 

below. These DQOs were developed in accordance with the USEPA’s seven-step iterative 

process (USEPA 2006). 

4.1 PROBLEM STATEMENT

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

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

environmental contaminants that are garnering increasing regulatory interest due to their 

potential risks to human health and the environment. The regulatory framework for managing 

PFAS at both the federal and state level continues to evolve. 

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

of risk-based SLs for soil and groundwater, as described in a memorandum from the Office of 

the Secretary of Defense (OSD) dated 15 September 2021 (Deputy Assistant Secretary of 

Defense 2021). The ARNG program under which this SI was performed allows/follows this DoD 

policy. Should the maximum site concentration for sampled media exceed the SLs established in 

the OSD memorandum, the site will proceed to the next phase under CERCLA. The SLs 

established in the OSD memorandum apply to three compounds: PFOS, PFOA, and PFBS. 

Additionally, USEPA issued drinking water lifetime HAs for PFOA and PFOS in May 2016 

(USEPA 2016a, 2016b). The USEPA lifetime HAs may also be used as SLs for groundwater 

samples collected at the facility boundary where off-facility drinking water wells are present 

downgradient. This determination will be based on localized groundwater flow direction 

established during the SI. The SLs are presented in Section 6.1 of this SI Report.

The following quotes from the U.S. Department of the Army (DA) policy documents form the 

basis for this project (DA 2016b, 2018): 

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

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

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

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

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

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

areas. In additions, metal plating operations, which used certain PFOS-containing mist 

suppressants, shall be considered possible source areas.”

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

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

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

contamination.”
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• “Identify sites where perfluorinated compounds are known or suspected to have been 

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

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

4.2 GOALS OF THE STUDY

The goals of the SI include the following:

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

• Develop information to potentially eliminate a release from further consideration because 

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

• Determine the potential need for a TCRA (applies to drinking water only). The primary 

actions that will be considered include provision of alternative water supplies or wellhead 

treatment. 

• Collect or develop data to evaluate the release. 

• Collect data to better characterize the release for more effective and rapid initiation of an 

RI. 

• If PFOA, PFOS, and PFBS are determined to be present, aim to evaluate whether the 

concentrations can be attributed to on-facility or off-facility sources that were identified 

within 4 miles of the installation as part of the PA (e.g., fire stations, major 

manufacturers, other DoD facilities).

4.3 INFORMATION INPUTS

Primary information inputs for the SI include the following:

• The PA Report for the Duncan RC and AASF;

• Analytical data collected during other environmental sampling efforts at the Duncan RC 

and AASF;

• Groundwater, surface water, soil and/or sediment sample data collected in accordance 

with the Uniform Federal Policy (UFP) − Quality Assurance Project Plan (QAPP)

Addendum (EA 2021b); and

• Field data collected including groundwater elevation and water quality parameters 

measured using a multi-parameter water quality meter.
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4.4 STUDY BOUNDARIES

The scope of the SI was bounded horizontally by the property limits of the facility (Figure 2-1). 

Off-facility sampling was not included in the scope of this SI. If future offsite sampling is 

required, the proper stakeholders will be notified, and necessary rights of entry will be obtained 

by ARNG with property owner(s). The scope of the SI was vertically bounded as follows: 

groundwater (25−40 ft bgs), soil from hand auger borings (0−2 ft bgs) and soil from direct-push 

technology (DPT) borings (30−40 ft bgs). 

4.5 ANALYTICAL APPROACH

Samples were analyzed by Eurofins Lancaster Laboratories Env, LLC, accredited under the DoD 

Environmental Laboratory Accreditation Program (DoD ELAP; Accreditation No. 1.01) and 

approved by the Hazardous Substances Cleanup Act Program, per DNREC requirement. PFAS 

data underwent 100% Stage 2B validation in accordance with the DoD General Data Validation 

Guidelines (2019) and DoD Data Validation Guidelines Module 3: Data Validation Procedure of 

Per- and Polyfluoroalkyl Substances Analysis by Quality Systems Manual (QSM) Table B-15 

(2020).

PFAS data were compared to applicable SLs and decision rules as defined in the UFP-QAPP 

addendum (EA 2021b). Decision rules were developed for groundwater and soil. These rules 

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

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

based on the following:

Groundwater:

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

2. What are the concentrations of PFOA, PFOS, and PFBS constituents at the potential 

source area?

3. What is the concentration of PFOA, PFOS, and PFBS constituents at the boundary?

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

Soil:

1. What is the concentration of PFOA, PFOS, and PFBS constituents in shallow surface soil 

(0−2 ft bgs)?

2. What is the concentration of PFOA, PFOS, and PFBS constituents in soil (i.e., capillary 

fringe and bedrock interface) (2−39 ft bgs)?

3. What does the CSM suggest in terms of source, pathway, and receptor?
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4.6 DATA USABILITY ASSESSMENT

The Data Usability Assessment is an evaluation at the conclusion of data collection activities that 

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

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

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

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

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

Data Quality Indicators (DQIs) (precision, accuracy, representativeness, comparability, 

completeness, and sensitivity) are important components in assessing data usability. These DQIs 

are evaluated in the subsequent sections. The results of the evaluation demonstrate that the data 

presented in this SI report are of high quality overall. Although most of the SI data are 

considered reliable, a subset of the data was qualified to indicate increased uncertainty due to 

quality issues. Specific factors that contribute to uncertainty in the dataset are described below. 

The Data Validation Report (Appendix A) presents explanations for all qualified data in greater 

detail. 

4.6.1 Precision 

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

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

sampling precision is measured with the field duplicate relative percent differences (RPDs), and 

laboratory precision is measured with RPDs for laboratory duplicates, such as laboratory control 

sample (LCS) and laboratory control sample duplicate (LCSD) pairs and matrix spike (MS) and 

matrix spike duplicate (MSD) pairs. 

LCS/LCSD pairs were prepared by addition of known concentrations of each analyte to a matrixfree media known to be free of target analytes. Results for LCS/LCSD pairs met the criterion of 

RPD≤30%, as specified in the QAPP Addendum (EA 2021b), demonstrating that the analytical 

system was in control during sample preparation and analysis. 

MS/MSD pairs were prepared, analyzed, and reported for each preparation batch at a rate of 5%.

MS/MSD results for PFAS met the criterion of RPD≤30%, as specified in the QAPP Addendum 

(EA 2021b), demonstrating good analytical precision for the matrix being tested. The MS/MSD 

pairs analyzed for TOC and laboratory duplicate analyzed for pH had RPDs of 4-5%.

Field duplicate samples were collected at a rate of 10% and analyzed for PFAS to assess the 

overall sampling and measurement precision for this sampling effort. The field duplicate samples 

were within the project established precision limits presented in the UFP-QAPP Addendum 

(50% for solid samples, 30% for water samples) (EA 2021b) or differences were less than the 

average limit of quantitation (LOQ), indicating acceptable sampling and analytical precision. 

No data were qualified due to issues with precision.
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4.6.2 Accuracy

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

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

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

result. Accuracy is measured through percent recoveries in calibration verification samples, 

LCS/LCSD, and MS/MSD, and through extraction internal standards (EIS). 

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

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

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

preparation and analysis, with the following exceptions. Perfluorooctanesulfonamide (PFOSA) 

recoveries were high at 190% and 187% in the LCS and LCSD, respectively. Because the 

LCS/LCSD indicated positive bias and PFOSA was not detected in the 12 associated samples, no 

data qualifying action was required. 

MS/MSDs were performed on soil samples AOI01-HA-04-1 (PFAS), DAASF-03-SB-14-15 

(PFAS and TOC), A0101-01-SB-13.5-14 (TOC), and groundwater sample MW15-GW (PFAS). 

Analyte recoveries in MS/MSD samples demonstrated that the analytical system was in control 

for both soil and water. Three analytes were outside acceptance limits in the MS and/or MSD 

performed on sample MW15-GW; however, the concentrations of these analytes detected in the 

parent sample were greater than four times the spike concentration, and therefore no data 

qualifying action was required. 

EIS for PFAS were added by the laboratory during sample extraction to measure relative 

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

sample preparation efficiencies, injection volume variances, mass spectrometry ionization 

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

displayed EIS area counts less than the lower quality control (QC) limit of 50%. Two positive 

field sample results were associated with EIS recoveries less than the QC limit, but greater than 

20%, and were qualified “J+”; these qualified results are considered usable as estimated values 

with a positive bias. Eight non-detect field sample results associated with EIS recoveries less 

than the QC limit, but greater than 20%, were qualified “UJ”; these qualified results are also 

considered usable. The non-detect results for N-methylperfluorooctane sulfonamidoacetic acid 

(NMeFOSAA) and N-ethylperfluorooctane sulfonamidoacetic acid (NEtFOSAA) in three soil

samples were associated with EIS recoveries less than 20%, and were qualified “X” by the 

validator, indicating that these results needed further evaluation during the data usability 

assessment. The project team determined these qualified results were usable for project purposes, 

and these six NMeFOSAA and NEtFOSAA soil results were therefore UJ qualified. 

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

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

the project established precision limits presented in the UFP-QAPP Addendum (EA 2021b).
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4.6.3 Representativeness

Representativeness qualitatively expresses the degree to which data accurately reflect site 

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

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

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

interferences. 

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

established in PFAS by LC/MS/MS compliant with QSM Version 5.3 Table B-15, including the 

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

all the ion transitions identified in table B-15 were monitored, standards that contained both 

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

used for quantitation. The laboratory also followed the required methods for analysis of pH 

(USEPA SW-846 Method 9045D) and TOC (USEPA SW-846 Method 9060A). The laboratory 

used approved standard methods in accordance with the UFP-QAPP Addendum (EA 2021b) for 

all analyses. 

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

duplicates were collected at a rate of 10% for analysis of PFAS and MS/MSD samples were 

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

and maximum holding times for extraction and analysis were met by the laboratory. 

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

control. Instrument blanks and method blanks were non-detect for all target analytes.

The potable water that was used for decontamination of drilling equipment was analyzed at the 

laboratory for PFAS by LC/MS/MS compliant with QSM 5.3 Table B-15 prior to field activities. 

This source water sample was non-detect for all target analytes. The laboratory results for the 

source water sample are provided in appendix F and the data validation report is provided in 

appendix A.

Equipment blanks (EBs) and field blanks (FBs) were also collected for groundwater and soil 

samples for analysis of PFAS. All FBs were non-detect for target analytes. PFOS was above the 

detection limit in an EB associated with eight groundwater samples. Three detections of PFOS in

associated field samples were less than five times the concentration detected in the blank, but 

greater than the LOQ, and were qualified “J+.” These qualified results are considered usable as 

estimated values with a positive bias. Two detections of PFOS in associated field samples that 

were less than the limit of detection were qualified as “U.” These results are usable as qualified 

and treated as non-detects. PFOS detections in associated samples that were greater than five

times the concentration detected in the blank were not qualified.

4.6.4 Comparability

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

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

analytical methods, units of reporting, and site selection procedures helps ensure comparability. 
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Standard field sampling and typical laboratory protocols were used during the SI and are 

considered comparable to ongoing investigations. 

4.6.5 Completeness

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

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

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

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

parameter is as follows and reflects the exclusion of “R” flagged data:

• PFAS in groundwater by LC/MS/MS compliant with QSM 5.3 Table B-15 at 100%;

• PFAS in soil by LC/MS/MS compliant with QSM 5.3 Table B-15 at 100%

• pH in soil by USEPA SW-846 Method 9045D at 100%; and 

• Total organic carbon (TOC) in soil by USEPA SW-846 Method 9060A at 100%.

4.6.6 Sensitivity 

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

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

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

study, and calibration standards at the LOQ. In order to meet the needs of the data users, project 

data must meet the measurement performance criteria for sensitivity and project LOQs specified 

in the UFP-QAPP Addendum (EA 2021b). The laboratory provided applicable calibration 

standards at the LOQ and reported all field sample results at the lowest possible dilution. 

Additionally, any analytes detected below the LOQ and above the detection limit were reported 

and qualified “J” as estimated values by the laboratory. 

4.6.7 Data Usability Summary

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

Sufficient usable data were obtained to meet the objectives of the SI and to complete the 

comparison to risk-based screening levels. 
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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 was 

implemented in accordance with the following approved documents. 

• Final Preliminary Assessment Report, Duncan Armory AASF, New Castle, Delaware, 

dated June 2020 (AECOM 2020);

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

Inspections for Per- and Polyfluoroalkyl Substances Impacted Sites, ARNG Installations, 

Nationwide. dated December 2020 (EA 2020a);

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

Addendum, Duncan Readiness Center and Army Aviation Support Facility, New Castle, 

Delaware dated May 2021 (EA 2021b);

• Final Programmatic Accident Prevention Plan dated November 2020 (EA 2020b); and

• Final Site Safety and Health Plan, Duncan Readiness Center and Army Aviation Support 

Facility, Delaware, dated February 2021 (EA 2021a). 

The SI field activities started on 27 May 2021 with a site visit with USACE, DEARNG, 

DNREC, and EA to review sample locations and perform utility clearance activities. The SI 

drilling, sampling, surveying, and site restoration activities were conducted from 2 to 3 June

2021 and included hand auger coring and surface soil sample collection, DPT boring and soil 

sample collection, temporary monitoring well installation, and grab groundwater sample 

collection. Field activities were conducted in accordance with the UFP-QAPP Addendum (EA 

2021b), except as noted in Section 5.8.

The following samples were collected during the SI and analyzed for a subset of 24 PFAS via 

LC/MS/MS compliant with QSM Version 5.3 Table B-15 to fulfill the project DQOs:

• Six surface soil samples from six locations (hand auger locations);

• 21 soil samples from seven locations (soil boring direct-push locations);

• Seven grab groundwater samples from seven temporary well locations; and

• One grab groundwater sample from one existing monitoring well location. 

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

list of samples collected for each medium. 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. Additionally, a photographic log of field activities is provided in 

Appendix C. 
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5.1 PRE-INVESTIGATION ACTIVITIES

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

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

water. Details of these activities are presented below. 

5.1.1 Technical Project Planning

The USACE TPP Process, Engineer Manual (EM) 200-1-2 (DA 2016a) defines four phases to 

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

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

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

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

identified in the PA. 

A combined TPP Meeting 1 and 2 was held on 19 March 2021, prior to SI field activities. 

Meeting minutes are provided in Appendix D. The combined TPP Meeting 1 and 2 was 

conducted in general accordance with EM 200-1-2. 

The stakeholders for this SI include ARNG, DEARNG, USACE, DNREC, representatives 

familiar with the facility, the regulations, and the community. Stakeholders were provided the 

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

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

the UFP-QAPP Addendum (EA 2021b). A future TPP meeting will provide an opportunity to 

discuss SI results and findings, and future actions, where warranted. 

5.1.2 Utility Clearance

EA contacted Miss Utility of Delmarva to notify them of intrusive work at the facility. Utility 

clearance was performed at each of the proposed boring locations on 27 May 2021 with input 

from the EA field team and DEARNG. General locating services were used to complete the 

clearance. Additionally, the first 5 ft of each boring were pre-cleared by EA’s drilling 

subcontractor, GSI Mid Atlantic, using a hand auger to verify utility clearance in shallow 

subsurface where utilities would typically be encountered. 

5.1.3 Source Water and PFAS Sampling Equipment Acceptability

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

PFAS-free prior to the start of field activities. A sample from a deionization water source at the 

EA Ecotoxicological Laboratory was collected on 31 March 2021, prior to mobilization, and 

analyzed for PFAS by LC/MS/MS compliant with QSM 5.3 Table B-15. A discussion of the 

results is presented in Section 4.6.3.

5.2 SOIL BORINGS AND SOIL SAMPLING

Soil samples were collected via DPT drilling methods in accordance with Standard Operating 

Procedure 047 Direct-Push Technology Sampling (EA 2021b). A Geoprobe® 7822DT dual-tube 
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sampling system was used to collect continuous soil cores to the target depth. A hand auger was 

used to collect soil from the top 5 ft of the boring in compliance with utility clearance 

procedures.

Three discrete soil samples were planned to be collected for PFAS analysis from each soil 

boring: one surface soil sample (collected from 0 to 2 ft bgs) and two subsurface soil samples. 

One subsurface soil sample was to be collected approximately 1 ft above the groundwater table 

and one was to be collected at the mid-point between the surface and the groundwater table (not 

to exceed 15 ft bgs). Groundwater was encountered at depths ranging from 20 to 40 ft bgs during 

drilling. Total boring completion depths, to accommodate temporary well installation, ranged 

from 25 to 45 ft bgs. Additionally, six surface soil locations (AOI01-HA-01 through AOI01-

HA-06) were completed to 2 ft bgs using a hand auger. One surface soil sample was taken from 

each hand auger boring. The soil borings are shown on Figure 5-1, and boring and sample 

depths are provided in Table 5-1. The soil boring locations were selected based on the AOI 

information provided in the PA (AECOM 2020) and as agreed upon by stakeholders during the 

TPP and review of the UFP-QAPP Addendum (EA 2021b).

During the mobilization, the soil cores were continuously logged for lithological descriptions by 

a field geologist using the Unified Soil Classification System. A photoionization detector was 

used to screen the breathing zone during boring activities as a part of personal safety 

requirements. Observations and measurements were recorded on sampling forms (Appendix B2) 

and in a non-treated field logbook. Depth interval, recovery thickness, photoionization detector

concentrations, moisture, relative density, Munsell color, and Unified Soil Classification System 

texture were recorded. The boring logs are provided in Appendix E. 

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

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

transported via FedEx under standard chain-of-custody procedures to the laboratory and 

analyzed for PFAS (LC/MS/MS compliant with QSM Version 5.3 Table B-15), TOC (USEPA 

SW-846 Method 9060A) and pH (USEPA SW-846 Method 9045D) in accordance with the UFPQAPP Addendum (EA 2021b).

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

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

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

was used, such as a hand auger for the shallow soil samples, EBs were collected at a rate of 5%

and analyzed for the same parameters as the soil samples. A temperature blank was placed in 

each cooler to ensure that samples were preserved at or below 6 degrees Celsius (°C) during 

shipment. 

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

sampling and surveying in accordance with the UFP-QAPP Addendum (EA 2021b). After 

removal of the casings, boreholes were abandoned using soil cuttings and bentonite chips. 

Borings were installed in grass areas to avoid disturbing concrete or asphalt surfaces so no 

additional restoration services were required.
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5.3 TEMPORARY WELL INSTALLATION AND GROUNDWATER GRAB 

SAMPLING

Seven temporary wells were installed using a GeoProbe® 7822DT dual-tube sampling system. 

Once the borehole was advanced to the desired depth at locations AOI01-01, AOI01-02, AOI01-

03, AOI02-01, DAASF-01, DAASF-02, and DAASF-03, a temporary well was constructed of a 

5-ft section of 3/4-inch Schedule 40 polyvinyl chloride (PVC) screen with sufficient casing to 

reach the ground surface. New PVC pipe and screen were used at each location to avoid crosscontamination between locations. The screen intervals for the temporary wells are provided in 

Table 5-2.

Seven temporary wells and one existing permanent well were sampled as part of the field efforts 

in accordance with existing plans. Groundwater samples were collected using an inertial pump 

with PFAS-free HDPE tubing. Each sample was collected in laboratory-supplied PFAS-free 

HDPE bottles and labeled using a PFAS-free marker or pen. 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) after each grab sample was collected in a separate container. Samples were packaged on ice 

and transported via FedEx under standard chain-of-custody procedures to the laboratory and 

analyzed for PFAS by LC/MS/MS compliant with QSM Version 5.3 Table B-15 in accordance 

with the UFP-QAPP Addendum (EA 2021b). 

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. Two FBs were collected in accordance with the UFPQAPP Addendum (EA 2021b). A temperature blank was placed in each cooler to ensure that 

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

5.4 EXISTING MONITORING WELL GROUNDWATER GRAB SAMPLING

An existing facility monitoring well, MW-15, was sampled as part of the field efforts in 

accordance with the UFP-QAPP Addendum (EA 2021b). MW-15 has a 2-inch diameter and is 

screened from 15-25 ft bgs. The groundwater samples were collected using a peristaltic pump 

with PFAS-free HDPE tubing. The samples were collected in a laboratory-supplied PFAS-free 

HDPE bottle and labeled using a PFAS-free marker. The monitoring well was 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 oxidationreduction potential) were measured using a water quality meter and recorded on the field 

sampling form during sample collection. Samples were packaged on ice and transported via 

FedEx under standard chain-of-custody procedures to the laboratory and analyzed for PFAS by 

LC/MS/MS compliant with QSM Version 5.3 Table B-15 in accordance with the UFP-QAPP 

Addendum (EA 2021b). 

5.5 SYNOPTIC WATER LEVEL MEASUREMENTS

Groundwater levels were used to monitor site-wide groundwater elevations and assess 

groundwater flow. Synoptic water level elevation measurements were collected from the newly 
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installed temporary monitoring wells and the existing well, which was taken from the survey 

mark on the northern side of the well casing. Groundwater elevation data is provided in 

Table 5-3. 

5.6 SURVEYING

The northern side of each new temporary well casing, and the existing well, were surveyed by a 

state licensed surveyor from Merestone Consultants, Inc. Surveying was accomplished using a 

real-time kinematic differential global positioning system. Positions were collected in the 

applicable Universal Transverse Mercator zone projection with World Geodetic System 1984 

datum (horizontal) and North American Vertical Datum 1988 (vertical). Surveying data were 

collected on 3 June 2021 and are provided in Appendix B3. 

5.7 INVESTIGATION-DERIVED WASTE

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

regulated federally. PFAS IDW generated during the SI is considered non-hazardous waste and 

was managed in accordance with the UFP-QAPP Addendum (EA 2021b). 

Soil IDW (i.e., soil cuttings) was placed back into the boring and liquid IDW (i.e., purge water, 

development water, and decontamination fluids) generated during the SI activities was 

containerized in one 55-gallon drum which was labeled and secured within the cold storage 

building. The soil and liquid IDW was not sampled prior to its release or containment and 

assumes the PFAS characteristics of the associated soil or groundwater samples collected from 

those source locations. Containerized liquid IDW will be treated with granular activated carbon 

(GAC) and discharged to the ground as outlined in the Letter Work Plan for InvestigationDerived Material Disposal (EA 2021c).

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.

5.8 LABORATORY ANALYTICAL METHODS

Samples were analyzed for a subset of 24 PFAS by LC/MS/MS compliant with QSM 

Version 5.3 Table B-15 at Eurofins Lancaster Laboratories Env, LLC, a DoD ELAP-certified 

laboratory. The 24 PFAS compounds analyzed as part of the ARNG SI program include the 

following: 

• 4:2 Fluorotelomer sulfonate (4:2 FTS)

• 6:2 Fluorotelomer sulfonate (6:2 FTS)

• 8:2 Fluorotelomer sulfonate (8:2 FTS)

• N-ethylperfluorooctane sulfonamidoacetic acid (NEtFOSAA) 

• N-methylperfluorooctane sulfonamidoacetic acid (NMeFOSAA)

• Perfluorobutane sulfonate (PFBS)

• Perfluorobutanoic acid (PFBA)
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• Perfluorodecane sulfonate (PFDS)

• Perfluorodecanoic acid (PFDA)

• Perfluorododecanoic acid (PFDoA)

• Perfluoroheptane sulfonate (PFHpS)

• Perfluoroheptanoic acid (PFHpA)

• Perfluorohexane sulfonate (PFHxS)

• Perfluorohexanoic acid (PFHxA)

• Perfluorononane sulfonate (PFNS)

• Perfluorononanoic acid (PFNA)

• Perfluorooctanesulfonamide (PFOSA)

• Perfluorooctane sulfonate (PFOS)

• Perfluorooctanoic acid (PFOA)

• Perfluoropentane sulfonate (PFPS)

• Perfluoropentanoic acid (PFPeA)

• Perfluorotetradecanoic acid (PFTeDA)

• Perfluorotridecanoic acid (PFTrDA)

• Perfluoroundecanoic acid (PFUnA).

Soil samples were also analyzed for TOC using USEPA Method 9060A, pH by USEPA SW-846 

Method 9045D and grain size by ASTM D422.

5.9 DEVIATIONS FROM UFP-QAPP ADDENDUM

Deviations from the UFP-QAPP Addendum occurred based on field conditions. These deviations 

were discussed between EA, ARNG, USACE, and DNREC. Four deviations from the UFPQAPP Addendum are noted below: 

• Two temporary well boring locations, AOI01-01 and DAASF-03, were advanced to 45 ft 

bgs due to the encountered depth of groundwater. This deviation from the UFP-QAPP 

Addendum was discussed with and approved of by ARNG, USACE, and DNREC. 

• Temporary wells were constructed of 3⁄4-inch Schedule 40 PVC as opposed to the 1-inch 

Schedule 40 PVC that was proposed in the UFP-QAPP Addendum.

• Due to depth of some of the temporary wells (greater than predicted by available data), a 

peristaltic pump could not generate enough lift to bring groundwater to the surface; 

therefore, groundwater samples were collected using a stainless-steel check valve inertial 

pump. When using the inertial pump, a minimum of five well volumes of water was 

removed from each temporary well prior to recording water quality parameters and 

collecting the sample. 

• Field duplicate samples were not collected and analyzed for total organic carbon or pH. 

Total organic carbon and pH are not undergoing formal data validation. These analyses 

are receiving data verification only. 
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Table 5-1.

Samples by Medium

Duncan RC and AASF, New Castle, Delaware

Site Inspection Report

Sample Identification

Sample 

Collection 

Date

Sample Depth

(ft bgs)

PFAS(USEPA Method 537 Modified)TOC(USEPA SW-846Method 9060A)pH (USEPA SW-846 Method 9045D)

Comments

Soil Samples

AOI01-01-SB-1-2 06/02/2021 1-2 X

AOI01-01-SB-13.5-14 06/02/2021 13.5-14 X X X

AOI01-01-SB-34.5-35.5 06/02/2021 34.5-35.5 X

AOI01-02-SB-1-2 06/02/2021 1-2 X

AOI01-02-SB-14-15 06/02/2021 14-15 X

AOI01-02-SB-19-20 06/02/2021 19-20 X

AOI01-03-SB-1-2 06/02/2021 1-2 X

AOI01-03-SB-14-15 06/02/2021 14-15 X

AOI01-03-SB-22-23 06/02/2021 22-23 X

AOI02-01-SB-1-2 06/02/2021 1-2 X

AOI02-01-SB-14-15 06/02/2021 14-15 X

AOI02-01-SB-21-22 06/02/2021 21-22 X

DAASF-01-SB-1-2 06/02/2021 1-2 X

DAASF-01-SB-14-15 06/02/2021 14-15 X

DAASF-01-SB-31-32 06/02/2021 31-32 X

DAASF-02-SB-1-2 06/02/2021 1-2 X

DAASF-02-SB-14-15 06/02/2021 14-15 X

DAASF-SB-FD1 06/02/2021 14-15 X Field Duplicate

DAASF-02-SB-34-35 06/02/2021 34-35 X

DAASF-03-SB-1-2 06/03/2021 1-2 X

DAASF-SB-FD2 06/03/2021 1-2 X Field Duplicate

DAASF-03-SB-14-15 06/03/2021 14-15 X X X

DAASF-03-SB-36-37 06/03/2021 36-37 X

AOI01-HA-01-1 06/02/2021 1 X

DAASF-HA-FD1 06/02/2021 1 X Field Duplicate

AOI01-HA-02-1 06/02/2021 1 X

AOI01-HA-03-1 06/02/2021 1 X

AOI01-HA-04-1 06/02/2021 1 X

AOI01-HA-05-1 06/02/2021 1 X

AOI01-HA-06-1 06/02/2021 1 X

Groundwater Samples

AOI01-01-GW 06/03/2021 X

AOI01-02-GW 06/03/2021 X

AOI01-03-GW 06/03/2021 X

AOI02-01-GW 06/03/2021 X

DAASF-01-GW 06/03/2021 X

DAASF-GW-FD 06/03/2021 X Field Duplicate

DAASF-02-GW 06/03/2021 X

DAASF-03-GW 06/03/2021 X

MW15-GW 06/03/2021 X
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Table 5-1.

Samples by Medium

Duncan RC and AASF, New Castle, Delaware

Site Inspection Report

Sample Identification

Sample 

Collection 

Date

Sample Depth

(ft bgs)

PFAS(USEPA Method 537 Modified)TOC(USEPA SW-846Method 9060A)pH (USEPA SW-846 Method 9045D)

Comments

Blank Samples

DAASF-FB01 06/02/2021 - X Field Blank

DAASF-FB02 06/03/2021 - X Field Blank

DAASF-EB01 06/02/2021 - X Equipment Blank

DAASF-GW-EB1 06/03/2021 - X Equipment Blank

DAASF-SB-EB03 06/03/2021 - X Equipment Blank
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Table 5-2.

Soil Boring Depths and Temporary Well Screen Intervals

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Site Inspection Report

Area of Interest Boring Location

Soil Boring Depth

(ft bgs)

Temporary Well 

Screen Interval

(ft bgs)

AOI 1

AOI01-01 45.0 40.0-45.0

AOI01-02 25.0 20.0-25.0

AOI01-03 29.0 24.0-29.0

AOI01-HA-01 2.0 -

AOI01-HA-02 2.0 -

AOI01-HA-03 2.0 -

AOI01-HA-04 2.0 -

AOI01-HA-05 2.0 -

AOI01-HA-06 2.0 -

AOI 2 AOI02-01 29.0 24.0-29.0

Duncan RC and AASF Boundary

DAASF-01 37.5 32.5-37.5

DAASF-02 40.0 35.0-40.0

DAASF-03 45.0 40.0-45.0

Table 5-3.

Groundwater Elevation

Duncan RC and AASF, New Castle, Delaware

Site Inspection Report

Monitoring Well 

Identification

Top of Casing Elevation

(ft amsl)

Depth to Water

(ft btoc)

Groundwater Elevation

(ft amsl)

AOI01-01 70.56 39.4 31.16

AOI01-02 51.42 20.8 30.62

AOI01-03 53.64 23.9 29.74

AOI02-01 50.08 22.16 27.92

DAASF-01 63.41 32.52 30.89

DAASF-02 68.54 35.65 32.89

DAASF-03 64.91 35.62 29.29

MW-15 37.88 12.0 25.88

Note: 

btoc = Below top of casing.
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 5-10

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Army National Guard Site Inspections

Site Inspection Report

Duncan RC and AASF, Delaware

Figure 5-1

Site Inspection Sample Locations

<!

MW-15

DAASF-03

DAASF-02

DAASF-01

AOI02-01

AOI01-03

AOI01-02

AOI01-01

AOI01-HA-04

AOI01-HA-05

AOI01-HA-03

AOI01-HA-06

AOI01-HA-02

AOI01-HA-01

3

0 200

Feet

Facility Data

Facility Boundary

Area of Interest

Potential PFAS Release

Sample Locations

DPT Boring/Temporary

Well Location

<! Existing Facility Well Location

Hand Auger Soil Location

Hydrology/Hydrogeology

Surface Water Flow Direction

Groundwater Flow Direction

Retention Pond

Wetlands

DE

^_

Data Sources:

ESRI 2020

AECOM 2020

Path: \\lovetongis\GISdata\Federal\Nationwide\PFAS\MAES_634250383\PROJECTS\SIReport\DuncanArmory\DuncanArmory.aprx

Date:.......................February 2021

Prepared By:.............................EA

Prepared For:....................USACE

Projection:.......WGS 84 UTM 18N
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EA Engineering, Science, and Technology, Inc., PBC 5-12

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Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 6-1

6. SITE INSPECTION RESULTS

This section presents the analytical results of the SI for each AOI. The analytical results are 

reported and evaluated in the subsequent sections. The SLs used in this evaluation are presented 

in Section 6.1. A discussion of the results for each AOI is provided in Section 6.3 and 

Section 6.4. Table 6-2 through Table 6-4 present PFAS results for samples with detections in 

soil and groundwater; only constituents detected in one or more samples are included. Tables 

that contain all results are provided in Appendix F, and the laboratory reports are provided in 

Appendix G. 

6.1 SCREENING LEVELS

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

SLs for soil and groundwater, as described in a memorandum from the OSD dated 15 September 

2021 (Deputy Assistant Secretary of Defense 2021). 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, and the exceedances be attributed to 

ARNG, the site will proceed to the next phase under CERCLA, which is an RI. The SLs apply to 

three compounds, PFOA, PFOS, and PFBS, for both soil and groundwater, as presented in 

Table 6-1. 

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

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

contain PFAS within the boundaries of the facility. 

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

Analyte

Residential

(Soil)

(μg/kg)1

Industrial / Commercial

Composite Worker

(Soil)

(μg/kg) 1

Tap Water

(Groundwater)

(ng/L) 1

PFOA 130 1,600 40

PFOS 130 1,600 40

PFBS 1,900 25,000 600

Notes:

1. Deputy Assistant Secretary of Defense. 2021. Risk-Based Screening Levels Calculated for PFOS, PFOA, 

PFBS in Groundwater and Soil using USEPA’s Regional Screening Level Calculator. Hazard Quotient 

(HQ)=0.1. 15 September 2021. 

6.2 SOIL PHYSICOCHEMICAL ANALYSES

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

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

of the TOC and pH sampling. 

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

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

Technology Regulatory Council (ITRC), several important PFAS partitioning mechanisms 
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 6-2

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 – HELICOPTER CRASH SITE

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

AOI 1, which includes the Helicopter Crash Site. The detected compounds are summarized in 

Table 6-2 through Table 6-4. Figures 6-1 through Figure 6-4 present detections for PFOS, 

PFBS and PFOA in soil and groundwater.

6.3.1 Soil Analytical Results

PFOA, PFOS, and PFBS concentrations in soil, when detected, did not exceed the soil SLs at 

AOI 1. Tables 6-2 and Table 6-3 summarize the detected compounds in soil. Figure 6-1 and 

Figure 6-2 present the ranges of detections for PFOS, PFBS and PFOA in soil. 

Soil was sampled in nine boring locations associated with one potential release area at AOI 1. 

Soil was sampled from three intervals at locations AOI01-01, AOI01-02, and AOI01-03, and one

surface interval at locations AOI01-HA-01 through AOI01-HA-06. 

PFOS was detected in the surface interval (1−2 ft bgs) of all boring locations, at concentrations 

ranging from 0.32 J microgram per kilogram (μg/kg) (AOI01-HA-04) to 6.9 μg/kg (AOI01-

HA-03), below the SL of 130 μg/kg. PFOA was detected in all surface interval soil samples, 

except for boring locations AOI01-HA-04 and AOI-01-HA-05. PFOA concentrations ranged 

from 0.30 J μg/kg (AOI01-HA-01) to 1.3 μg/kg (AOI01-01), well below the SL of 130 μg/kg. 

PFBS was not detected in any surface interval samples. 

PFOS was detected in one subsurface soil interval (13.4−14.0 ft bgs) at location AOI01-01, at a 

concentration of 0.67 μg/kg, below the SL of 1,600 μg/kg. PFOA was detected in the subsurface 

soil samples taken from both intervals (14−15 ft bgs and 22−23 ft bgs) at location AOI01-03, at 

concentrations of 0.22 J μg/kg and 0.27 J μg/kg, respectively. PFOA detections are below the SL 

of 1,600 μg/kg. PFBS was not detected in any subsurface interval samples. 

6.3.2 Groundwater Analytical Results 

Groundwater samples were collected from three temporary wells associated with one potential 

release area at AOI 1. PFOS and PFOA were detected in groundwater at concentrations 

exceeding the SL of 40 ng/L. Location AOI01-01, immediately west of the crash site, had a 

PFOA concentration of 120 ng/L. PFOS and PFBS were also detected in groundwater at this 

location; however, the detections did not exceed their associated SLs. Location AOI01-02, 

located west of the crash site within a man-made stormwater detention pond, had a PFOS 
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detection of 150 ng/L. PFOA and PFBS were also detected in groundwater at this location; 

however, the detections did not exceed their associated SLs. Location AOI01-03, located north

of the detention pond and location AOI01-02, had a PFOS detection of 75 ng/L. PFOA and 

PFBS were also detected in groundwater at these locations; however, the detections did not 

exceed their respective SLs. PFBS detections in groundwater at the three locations ranged from 

2.1 ng/L to 8.6 ng/L, well below the SL of 600 ng/L. PFOS detections in groundwater at the 

three locations ranged from 32 ng/L (AOI01-01) to 150 ng/L and PFOA detections ranged from 

23 ng/L (AOI01-02) to 120 ng/L. 

The detected compounds from groundwater are summarized in Table 6-4. Figure 6-3 presents

the ranges of detections for PFOS and PFOA. 

6.3.3 Conclusions

Based on the results of the SI, PFBS was not detected in soil at AOI 1, and PFOS and PFOA 

were detected several orders of magnitude lower than the soil SLs. PFBS was detected in 

groundwater at concentrations below the SL at all locations. PFOS or PFOA were detected in 

groundwater at concentrations exceeding the individual SLs of 40 ng/L in all three temporary 

well locations associated with AOI 1. Based on the exceedances of the SL for PFOS and PFOA 

in groundwater, further evaluation at AOI 1 is warranted.

6.4 AOI 2 – HANGAR

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

AOI 2, which includes the facility hangar. The detected compounds are summarized in Table 6-2

through Table 6-4. Figures 6-1 through Figure 6-4 present detections for PFOS, PFBS, and 

PFOA in soil and groundwater.

6.4.1 Soil Analytical Results

PFOA, PFOS, and PFBS concentrations in soil, when detected, did not exceed the soil SLs at 

AOI 2. Tables 6-2 and Table 6-3 summarize the detected compounds in soil. Figure 6-1 and 

Figure 6-2 present the ranges of detections for PFOS and PFOA in soil. 

Soil was sampled from three intervals in one boring location (AOI02-01) associated with one 

potential release area at AOI 2.

PFOS and PFOA were detected in the surface interval (1−2 ft bgs) with concentrations of 

0.31 J μg/kg and 0.64 μg/kg, respectively, below the SL of 130 μg/kg. There were no detections 

of PFOS or PFOA in the subsurface soil sample intervals at this location. PFBS was not detected 

in any surface or subsurface interval samples.

6.4.2 Groundwater Analytical Results 

Groundwater samples were collected from one temporary well associated with one potential 

release area at AOI 2, located north and hydraulically downgradient of the facility hangar as well 

as the 1970s Helicopter crash site. PFOA was detected in groundwater at a concentration of 
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

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230 ng/L, exceeding the SL of 40 ng/L. PFOS and PFBS were also detected at this location; 

however, the detections did not exceed their associated SLs (5.7 J+ ng/L and 3.5 ng/L, 

respectively).

The detected compounds from groundwater are summarized in Table 6-4. Figure 6-3 presents

the ranges of detections for PFOS and PFOA. 

6.4.3 Conclusions

Based on the results of the SI, PFBS was not detected in soil at AOI 2, and PFOS and PFOA 

were detected several orders of magnitude lower than the soil SLs. PFBS and PFOS were 

detected in groundwater at concentrations below the SL. PFOA was detected in groundwater at a 

concentration exceeding the individual SL of 40 ng/L. Based on the exceedance of the SL for 

PFOA in groundwater, further evaluation at AOI 2 is warranted. 

6.5 BOUNDARY SAMPLE LOCATIONS

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

facility boundary. The detected compounds are summarized in Table 6-2 through Table 6-4. 

Figure 6-1 through Figure 6-4 present the ranges of detections for PFOS and PFOA. 

6.5.1 Soil Analytical Results

PFOA, PFOS, and PFBS concentrations in soil, when detected, did not exceed the soil SLs at the 

facility boundary. Tables 6-2 and Table 6-3 summarize the detected compounds in soil. Figure 

6-1 and Figure 6-2 present the ranges of detections for PFOS and PFOA in soil. 

Soil was sampled from three intervals in three boring locations along the facility boundary: one 

sample location at the southwestern corner of the facility (DAASF-01), adjacent to the DANG 

Fire Training area, and two locations along the eastern facility boundary (DAASF-02 and 

DAASF-03). 

PFOS was detected in the surface interval (1−2 ft bgs) at these locations with concentrations 

ranging from 0.24 J μg/kg to 1.6 μg/kg, below the SL of 130 μg/kg. PFOA was detected within 

the surface interval at these locations with concentrations ranging from 0.52 J μg/kg to 

1.2 μg/kg. PFOA was detected in the 14–15 ft bgs soil interval at locations DAASF-01 

(0.77 μg/kg) and DAASF-03 (0.24 J μg/kg), below the SL of 130 μg/kg. PFBS was not detected 

in any surface or subsurface interval samples.

6.5.2 Groundwater Analytical Results 

Groundwater samples were collected from three temporary well locations along the facility 

boundary (DAASF-01, DAASF-02, and DAASF-03) and one facility monitoring well (MW-15), 

located in the northernmost, downgradient corner of the facility. While PFOA and PFBS were 

detected in groundwater at location DAASF-01, there were no exceedances of the associated 

SLs. Additionally, PFOS was non-detect in groundwater at this location. PFOA was detected at 

levels which exceed the 40 ng/L SL in groundwater at locations DAASF-02 and DAASF-03, 
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with concentrations of 150 ng/L and 280 ng/L, respectively. PFOA was detected in groundwater 

at location MW-15 with a concentration of 100 ng/L, exceeding the SL. PFBS and PFOS were 

detected in groundwater at all three locations, below their respective SLs. 

The detected compounds from groundwater are summarized in Table 6-4. Figure 6-3 present the 

ranges of detections for PFOS and PFOA. 

6.5.3 Conclusions

Based on the results of the SI, PFBS was not detected in soil at the boundary, and PFOS and 

PFOA were detected several orders of magnitude lower than the soil SLs. PFBS was detected in 

groundwater at concentrations below the SL at all locations. PFOS was detected in groundwater 

at concentrations below the SL at all locations, except at location DAASF-01. DAASF-01 had no 

detection of PFOS. PFOA was detected in groundwater at concentrations exceeding the 

individual SLs of 40 ng/L in temporary well locations DAASF-02 and DAASF-03, as well as the 

facility monitoring well location (MW-15). Based on the exceedance of the SL for PFOA in 

groundwater, further evaluation is warranted. 
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

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Table 6-2 PFAS Detections in Surface Soil, 

Site Inspection Report, Duncan RC and AASF

Analyte Screening Level 1 Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual

Soil, PFAS (EPA 537) (ng/g)

4:2 Fluorotelomer sulfonate (4:2 FTS) - < 1.7 2.1 U < 1.7 2.2 U < 1.6 2.0 U < 1.8 2.3 U < 1.9 2.3 UJ < 1.8 2.3 U < 2.2 2.8 U < 1.7 2.1 U < 1.8 2.2 U < 1.8 2.3 U < 1.7 2.1 U < 1.7 2.1 U < 1.7 2.1 U < 1.7 2.1 UJ < 1.7 2.1 U

6:2 Fluorotelomer sulfonate (6:2 FTS) - < 1.7 2.1 U < 1.7 2.2 U < 1.6 2.0 U < 1.8 2.3 U < 1.9 2.3 UJ < 1.8 2.3 U < 2.2 2.8 U < 1.7 2.1 U < 1.8 2.2 U < 1.8 2.3 U < 1.7 2.1 U < 1.7 2.1 U < 1.7 2.1 U < 1.7 2.1 U < 1.7 2.1 U

8:2 Fluorotelomer sulfonate (8:2 FTS) - < 1.7 3.2 U < 1.7 3.2 U < 1.6 3.1 U < 1.8 3.4 U < 1.9 3.5 U < 1.8 3.4 U < 2.2 4.2 U < 1.7 3.2 U < 1.8 3.3 U < 1.8 3.4 U < 1.7 3.2 U < 1.7 3.2 U < 1.7 3.2 U < 1.7 3.2 U < 1.7 3.2 U

N-ethyl perfluorooctanesulfonamidoacetic acid (NEtFOSAA) - < 0.42 2.1 U < 0.43 2.2 U < 0.41 2.0 U < 0.45 2.3 U < 0.47 2.3 X < 0.46 2.3 U < 0.56 2.8 U < 0.43 2.1 U < 0.44 2.2 U < 0.46 2.3 U < 0.43 2.1 U < 0.43 2.1 U < 0.43 2.1 U < 0.42 2.1 X < 0.43 2.1 X

N-methyl perfluorooctanesulfonamidoacetic acid (NMeFOSAA) - < 0.42 2.1 U < 0.43 2.2 U < 0.41 2.0 U < 0.45 2.3 U < 0.47 2.3 X < 0.46 2.3 U < 0.56 2.8 U < 0.43 2.1 U < 0.44 2.2 U < 0.46 2.3 U < 0.43 2.1 U < 0.43 2.1 U < 0.43 2.1 U < 0.42 2.1 X < 0.43 2.1 X

Perfluorobutanesulfonic acid (PFBS) 1,900 2 < 1.7 2.1 U < 1.7 2.2 U < 1.6 2.0 U < 1.8 2.3 U < 1.9 2.3 U < 1.8 2.3 U < 2.2 2.8 U < 1.7 2.1 U < 1.8 2.2 U < 1.8 2.3 U < 1.7 2.1 U < 1.7 2.1 U < 1.7 2.1 U < 1.7 2.1 U < 1.7 2.1 U

Perfluorobutanoic acid (PFBA) - 0.94 1.7 2.1 J < 1.7 2.2 U < 1.6 2.0 U < 1.8 2.3 U < 1.9 2.3 U < 1.8 2.3 U < 2.2 2.8 U < 1.7 2.1 U < 1.8 2.2 U < 1.8 2.3 U < 1.7 2.1 U < 1.7 2.1 U < 1.7 2.1 U < 1.7 2.1 U < 1.7 2.1 U

Perfluorodecanesulfonic acid (PFDS) - < 0.42 0.63 U < 0.43 0.65 U < 0.41 0.61 U < 0.45 0.68 U < 0.47 0.70 U < 0.46 0.69 U < 0.56 0.84 U < 0.43 0.64 U < 0.44 0.66 U < 0.46 0.68 U < 0.43 0.64 U < 0.43 0.64 U < 0.43 0.64 U < 0.42 0.64 U < 0.43 0.64 U

Perfluorodecanoic acid (PFDA) - 0.94 0.42 0.63 < 0.43 0.65 U < 0.41 0.61 U 0.26 0.45 0.68 J 0.25 0.47 0.70 J 0.33 0.46 0.69 J 2.0 0.56 0.84 0.24 0.43 0.64 J 0.76 0.44 0.66 0.67 0.46 0.68 J < 0.43 0.64 U < 0.43 0.64 U 0.42 0.43 0.64 J < 0.42 0.64 U < 0.43 0.64 U

Perfluorododecanoic acid (PFDoA) - 0.30 0.42 0.63 J < 0.43 0.65 U < 0.41 0.61 U < 0.45 0.68 U < 0.47 0.70 U 0.30 0.46 0.69 J 2.2 0.56 0.84 1.6 0.43 0.64 1.1 0.44 0.66 1.3 0.46 0.68 < 0.43 0.64 U < 0.43 0.64 U < 0.43 0.64 U < 0.42 0.64 U < 0.43 0.64 U

Perfluoroheptanesulfonic acid (PFHpS) - < 0.42 0.63 U < 0.43 0.65 U < 0.41 0.61 U < 0.45 0.68 U < 0.47 0.70 U < 0.46 0.69 U < 0.56 0.84 U < 0.43 0.64 U < 0.44 0.66 U < 0.46 0.68 U < 0.43 0.64 U < 0.43 0.64 U < 0.43 0.64 U < 0.42 0.64 U < 0.43 0.64 U

Perfluoroheptanoic acid (PFHpA) - 0.60 0.42 0.63 J < 0.43 0.65 U 0.27 0.41 0.61 J < 0.45 0.68 U < 0.47 0.70 U 0.23 0.46 0.69 J 0.37 0.56 0.84 J < 0.43 0.64 U < 0.44 0.66 U < 0.46 0.68 U < 0.43 0.64 U 0.42 0.43 0.64 J 0.25 0.43 0.64 J 0.45 0.42 0.64 J 0.39 0.43 0.64 J

Perfluorohexanesulfonic acid (PFHxS) - < 0.42 0.63 U < 0.43 0.65 U < 0.41 0.61 U < 0.45 0.68 U < 0.47 0.70 U < 0.46 0.69 U 1.1 0.56 0.84 < 0.43 0.64 U < 0.44 0.66 U 0.51 0.46 0.68 J < 0.43 0.64 U 1.7 0.43 0.64 < 0.43 0.64 U < 0.42 0.64 U < 0.43 0.64 U

Perfluorohexanoic acid (PFHxA) - 0.60 0.42 0.63 J < 0.43 0.65 U 0.22 0.41 0.61 J 0.23 0.45 0.68 J < 0.47 0.70 U < 0.46 0.69 U 0.40 0.56 0.84 J < 0.43 0.64 U < 0.44 0.66 U < 0.46 0.68 U < 0.43 0.64 U 0.50 0.43 0.64 J 0.26 0.43 0.64 J 0.37 0.42 0.64 J 0.38 0.43 0.64 J

Perfluorononanesulfonic acid (PFNS) - < 0.42 0.63 U < 0.43 0.65 U < 0.41 0.61 U < 0.45 0.68 U < 0.47 0.70 U < 0.46 0.69 U < 0.56 0.84 U < 0.43 0.64 U < 0.44 0.66 U < 0.46 0.68 U < 0.43 0.64 U < 0.43 0.64 U < 0.43 0.64 U < 0.42 0.64 U < 0.43 0.64 U

Perfluorononanoic acid (PFNA) - 1.5 0.42 0.63 0.31 0.43 0.65 J 0.37 0.41 0.61 J 0.32 0.45 0.68 J 0.27 0.47 0.70 J 0.43 0.46 0.69 J 0.65 0.56 0.84 J < 0.43 0.64 U < 0.44 0.66 U 0.26 0.46 0.68 J < 0.43 0.64 U 0.25 0.43 0.64 J 0.53 0.43 0.64 J 0.35 0.42 0.64 J 0.52 0.43 0.64 J

Perfluorooctanesulfonamide (PFOSA) - < 0.42 0.63 U < 0.43 0.65 U < 0.41 0.61 U < 0.45 0.68 U < 0.47 0.70 U < 0.46 0.69 U < 0.56 0.84 U < 0.43 0.64 U < 0.44 0.66 U < 0.46 0.68 U < 0.43 0.64 U < 0.43 0.64 U < 0.43 0.64 U < 0.42 0.64 U < 0.43 0.64 U

Perfluorooctanesulfonic acid (PFOS) 130 3 4.8 0.42 0.63 1.7 0.43 0.65 0.48 0.41 0.61 J 1.7 0.45 0.68 1.3 0.47 0.70 2.5 0.46 0.69 6.9 0.56 0.84 0.32 0.43 0.64 J 0.56 0.44 0.66 J 2.5 0.46 0.68 0.31 0.43 0.64 J 0.84 0.43 0.64 1.6 0.43 0.64 < 0.42 0.64 U 0.24 0.43 0.64 J

Perfluorooctanoic acid (PFOA) 130 3 1.3 0.42 0.63 0.35 0.43 0.65 J 0.77 0.41 0.61 0.38 0.45 0.68 J 0.30 0.47 0.70 J 0.32 0.46 0.69 J 0.74 0.56 0.84 J < 0.43 0.64 U < 0.44 0.66 U 0.32 0.46 0.68 J 0.64 0.43 0.64 1.0 0.43 0.64 0.52 0.43 0.64 J 1.2 0.42 0.64 0.99 0.43 0.64

Perfluoropentanesulfonic acid (PFPS) - < 0.42 3.2 U < 0.43 3.2 U < 0.41 3.1 U < 0.45 3.4 U < 0.47 3.5 U < 0.46 3.4 U < 0.56 4.2 U < 0.43 3.2 U < 0.44 3.3 U < 0.46 3.4 U < 0.43 3.2 U < 0.43 3.2 U < 0.43 3.2 U < 0.42 3.2 U < 0.43 3.2 U

Perfluoropentanoic acid (PFPA) - 0.94 0.42 0.63 < 0.43 0.65 U 0.28 0.41 0.61 J < 0.45 0.68 U 0.25 0.47 0.70 J+ < 0.46 0.69 U 0.75 0.56 0.84 J < 0.43 0.64 U < 0.44 0.66 U 0.29 0.46 0.68 J 0.30 0.43 0.64 J 0.37 0.43 0.64 J 0.40 0.43 0.64 J 0.61 0.42 0.64 J 0.64 0.43 0.64

Perfluorotetradecanoic acid (PFTeDA) - < 0.42 0.63 U < 0.43 0.65 U < 0.41 0.61 U < 0.45 0.68 U < 0.47 0.70 U < 0.46 0.69 U 0.84 0.56 0.84 1.1 0.43 0.64 0.81 0.44 0.66 0.60 0.46 0.68 J < 0.43 0.64 U < 0.43 0.64 U < 0.43 0.64 U < 0.42 0.64 U < 0.43 0.64 U

Perfluorotridecanoic acid (PFTriDA) - < 0.42 0.63 U < 0.43 0.65 U < 0.41 0.61 U < 0.45 0.68 U 0.24 0.47 0.70 J < 0.46 0.69 U 1.4 0.56 0.84 1.7 0.43 0.64 1.0 0.44 0.66 0.86 0.46 0.68 < 0.43 0.64 U < 0.43 0.64 U < 0.43 0.64 U < 0.42 0.64 U < 0.43 0.64 U

Perfluoroundecanoic acid (PFUnA) - 0.46 0.42 0.63 J < 0.43 0.65 U < 0.41 0.61 U < 0.45 0.68 U 0.26 0.47 0.70 J 0.25 0.46 0.69 J 4.0 0.56 0.84 1.0 0.43 0.64 1.4 0.44 0.66 1.6 0.46 0.68 < 0.43 0.64 U 0.34 0.43 0.64 J 0.28 0.43 0.64 J < 0.42 0.64 U < 0.43 0.64 U

Notes

J = Estimated concentration

U = The analyte was not detected at a level greater than or equal to the adjusted detection limit (DL)

X = Not validated

ng/g = Nanogram per gram

(1) The SL for soil is based on incidental ingestion of soil residential 0-2 ft.

(2) USEPA. 2021. Regional Screening Levels for Chemical Contaminants at Superfund Sites. On-Line Calculator. USEPA Office of Superfund. Https://www.epa.gov/risk/regional-screening-levels-rsls. Accessed 9 April.

(3) Deputy Assistant Secretary of Defense. 2019. Risk Based Screening Levels Calculated for PFOS, PFOA, PFBS in soil using USEPA’s RSL Calculator with HQ=0.1 (Deputy Assistant Secretary of Defense 2019).

Values exceeding the Screening Level are shaded gray

AOI = Area of Interest

ft = Feet

LOD = Limit of Detection

LOQ = Limit of Quantitation

Qual = Qualifier

< = analyte not detected above the LOD

Area of Interest AOI01 AOI02 DAASF

Location ID AOI01-01 AOI01-02 DAASF-03 DAASF-03

Sample Name AOI01-01-SB-1-2 AOI01-02-SB-1-2

AOI01-03 AOI01-HA-01 AOI01-HA-01 AOI01-HA-02 AOI01-HA-03 AOI01-HA-04 AOI01-HA-05 AOI01-HA-06 AOI02-01 DAASF-01 DAASF-02

DAASF-03-SB-1-2 DAASF-SB-FD2

Parent Sample ID

AOI01-03-SB-1-2 AOI01-HA-01-1 DAASF-HA-FD1 AOI01-HA-02-1 AOI01-HA-03-1 AOI01-HA-04-1 AOI01-HA-05-1 AOI01-HA-06-1 AOI02-01-SB-1-2 DAASF-01-SB-1-2 DAASF-02-SB-1-2

DAASF-03-SB-1-2-06032021

Depth 1 - 2 ft 1 - 2 ft

AOI01-HA-01-1-06022021

Sample Date 6/2/2021 6/2/2021

1 - 2 ft 1 ft 1 ft 1 ft 1 ft 1 ft 1 ft 1 ft 1 - 2 ft 1 - 2 ft 1 - 2 ft

6/2/2021 6/2/2021 6/2/2021

1 - 2 ft 1 - 2 ft

6/2/2021 6/2/2021 6/2/2021 6/2/2021 6/2/2021 6/2/2021 6/2/2021 6/2/2021 6/3/2021 6/3/2021
Table 6-3 - PFAS Detections in Subsurface Soil, 

Site Inspection Report, Duncan RC and AASF

Analyte Screening Level 1 Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual

 PFAS (ng/g)

- < 1.7 2.1 U < 1.8 2.3 U < 1.7 2.1 U < 1.8 2.3 U < 1.7 2.1 U < 1.7 2.1 U < 1.9 2.3 U < 1.8 2.2 U < 1.7 2.1 U < 1.9 2.3 U < 1.7 2.1 U < 1.7 2.1 U < 1.8 2.2 U < 1.8 2.2 U < 1.7 2.1 U

- < 1.7 2.1 U < 1.8 2.3 U < 1.7 2.1 U < 1.8 2.3 U < 1.7 2.1 U < 1.7 2.1 U < 1.9 2.3 U < 1.8 2.2 U < 1.7 2.1 U < 1.9 2.3 U < 1.7 2.1 U < 1.7 2.1 U < 1.8 2.2 U 2.5 1.8 2.2 < 1.7 2.1 U

- < 1.7 3.2 U < 1.8 3.4 U < 1.7 3.1 U < 1.8 3.4 U < 1.7 3.2 U < 1.7 3.2 U < 1.9 3.5 U < 1.8 3.4 U < 1.7 3.1 U < 1.9 3.5 U < 1.7 3.2 U < 1.7 3.1 U < 1.8 3.3 U < 1.8 3.3 U < 1.7 3.1 U

- < 0.43 2.1 U < 0.45 2.3 U < 0.41 2.1 U < 0.46 2.3 U < 0.42 2.1 U < 0.42 2.1 U < 0.47 2.3 U < 0.45 2.2 U < 0.42 2.1 U < 0.46 2.3 U < 0.42 2.1 U < 0.42 2.1 U < 0.44 2.2 UJ < 0.45 2.2 U < 0.42 2.1 UJ

- < 0.43 2.1 U < 0.45 2.3 U < 0.41 2.1 U < 0.46 2.3 U < 0.42 2.1 U < 0.42 2.1 U < 0.47 2.3 U < 0.45 2.2 U < 0.42 2.1 U < 0.46 2.3 U < 0.42 2.1 U < 0.42 2.1 U < 0.44 2.2 UJ < 0.45 2.2 UJ < 0.42 2.1 UJ

25,000 2 < 1.7 2.1 U < 1.8 2.3 U < 1.7 2.1 U < 1.8 2.3 U < 1.7 2.1 U < 1.7 2.1 U < 1.9 2.3 U < 1.8 2.2 U < 1.7 2.1 U < 1.9 2.3 U < 1.7 2.1 U < 1.7 2.1 U < 1.8 2.2 U < 1.8 2.2 U < 1.7 2.1 U

- < 1.7 2.1 U < 1.8 2.3 U < 1.7 2.1 U < 1.8 2.3 U < 1.7 2.1 U < 1.7 2.1 U < 1.9 2.3 U < 1.8 2.2 U < 1.7 2.1 U < 1.9 2.3 U < 1.7 2.1 U < 1.7 2.1 U < 1.8 2.2 U < 1.8 2.2 U < 1.7 2.1 U

- < 0.43 0.64 U < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U < 0.42 0.63 U < 0.42 0.64 U < 0.47 0.70 U < 0.45 0.67 U < 0.42 0.63 U < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U < 0.45 0.67 U < 0.42 0.63 U

- < 0.43 0.64 U < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U < 0.42 0.63 U < 0.42 0.64 U < 0.47 0.70 U < 0.45 0.67 U < 0.42 0.63 U < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U < 0.45 0.67 U < 0.42 0.63 U

- < 0.43 0.64 U < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U < 0.42 0.63 U < 0.42 0.64 U < 0.47 0.70 U < 0.45 0.67 U < 0.42 0.63 U < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U < 0.45 0.67 U < 0.42 0.63 U

- < 0.43 0.64 U < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U < 0.42 0.63 U < 0.42 0.64 U < 0.47 0.70 U < 0.45 0.67 U < 0.42 0.63 U < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U < 0.45 0.67 U < 0.42 0.63 U

- < 0.43 0.64 U < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U < 0.42 0.63 U < 0.42 0.64 U < 0.47 0.70 U < 0.45 0.67 U < 0.42 0.63 U < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U < 0.45 0.67 U < 0.42 0.63 U

- < 0.43 0.64 U < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U < 0.42 0.63 U < 0.42 0.64 U < 0.47 0.70 U < 0.45 0.67 U 0.21 0.42 0.63 J < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U < 0.45 0.67 U < 0.42 0.63 U

- < 0.43 0.64 U < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U < 0.42 0.63 U < 0.42 0.64 U < 0.47 0.70 U < 0.45 0.67 U < 0.42 0.63 U < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U 0.28 0.45 0.67 J < 0.42 0.63 U

- < 0.43 0.64 U < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U < 0.42 0.63 U < 0.42 0.64 U < 0.47 0.70 U < 0.45 0.67 U < 0.42 0.63 U < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U < 0.45 0.67 U < 0.42 0.63 U

- < 0.43 0.64 U < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U < 0.42 0.63 U < 0.42 0.64 U < 0.47 0.70 U < 0.45 0.67 U < 0.42 0.63 U < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U < 0.45 0.67 U < 0.42 0.63 U

- < 0.43 0.64 U < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U < 0.42 0.63 U < 0.42 0.64 U < 0.47 0.70 U < 0.45 0.67 U < 0.42 0.63 U < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U < 0.45 0.67 U < 0.42 0.63 U

1,600 3 0.67 0.43 0.64 < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U < 0.42 0.63 U < 0.42 0.64 U < 0.47 0.70 U < 0.45 0.67 U < 0.42 0.63 U < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U < 0.45 0.67 U < 0.42 0.63 U

1,600 3 < 0.43 0.64 U < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U 0.22 0.42 0.63 J 0.27 0.42 0.64 J < 0.47 0.70 U < 0.45 0.67 U 0.77 0.42 0.63 < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U 0.24 0.45 0.67 J < 0.42 0.63 U

- < 0.43 3.2 U < 0.45 3.4 U < 0.41 3.1 U < 0.46 3.4 U < 0.42 3.2 U < 0.42 3.2 U < 0.47 3.5 U < 0.45 3.4 U < 0.42 3.1 U < 0.46 3.5 U < 0.42 3.2 U < 0.42 3.1 U < 0.44 3.3 U < 0.45 3.3 U < 0.42 3.1 U

- < 0.43 0.64 U < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U < 0.42 0.63 U < 0.42 0.64 U < 0.47 0.70 U < 0.45 0.67 U < 0.42 0.63 U < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U 0.43 0.45 0.67 J < 0.42 0.63 U

- < 0.43 0.64 U < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U < 0.42 0.63 U < 0.42 0.64 U < 0.47 0.70 U < 0.45 0.67 U < 0.42 0.63 U < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U < 0.45 0.67 U < 0.42 0.63 U

- < 0.43 0.64 U < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U < 0.42 0.63 U < 0.42 0.64 U < 0.47 0.70 U < 0.45 0.67 U < 0.42 0.63 U < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U < 0.45 0.67 U < 0.42 0.63 U

- < 0.43 0.64 U < 0.45 0.68 U < 0.41 0.62 U < 0.46 0.69 U < 0.42 0.63 U < 0.42 0.64 U < 0.47 0.70 U < 0.45 0.67 U < 0.42 0.63 U < 0.46 0.70 U < 0.42 0.63 U < 0.42 0.63 U < 0.44 0.66 U < 0.45 0.67 U < 0.42 0.63 U

Notes

J = Estimated concentration

U = The analyte was not detected at a level greater than or equal to the adjusted detection limit (DL)

ng/g = Nanogram per gram

(1) The SL for soil is based on incidental ingestion of soil industrial/commercial worker >2 ft.

(2) USEPA. 2021. Regional Screening Levels for Chemical Contaminants at Superfund Sites. On-Line Calculator. USEPA Office of Superfund. Https://www.epa.gov/risk/regional-screening-levels-rsls. Accessed 9 April.

(3) Deputy Assistant Secretary of Defense. 2019. Risk Based Screening Levels Calculated for PFOS, PFOA, PFBS in soil using USEPA’s RSL Calculator with HQ=0.1 (Deputy Assistant Secretary of Defense 2019).

Values exceeding the Screening Level are shaded gray

AOI = Area of Interest

ft = Feet

LOD = Limit of Detection

LOQ = Limit of Quantitation

Qual = Qualifier

< = analyte not detected above the LOD

Cells exceeding the standard in Column B are shaded gray

6/2/2021 6/2/2021 6/2/2021 6/2/2021 6/2/2021 6/2/2021 6/2/2021 6/2/2021 6/2/2021 6/2/2021 6/3/2021 6/3/2021

14 - 15 ft 36 - 37 ft

Sample Date 6/2/2021 6/2/2021 6/2/2021

Depth 13.5 - 14 ft 34.5 - 35.5 ft 14 - 15 ft 19 - 20 ft 14 - 15 ft 22 - 23 ft 14 - 15 ft 21 - 22 ft 14 - 15 ft 31 - 32 ft 14 - 15 ft 34 - 35 ft 14 - 15 ft

DAASF-02-SB-14-15-06022021

DAASF-03-SB-14-15 DAASF-03-SB-36-37

Parent Sample ID

Sample Name AOI01-01-SB-13.5-14 AOI01-01-SB-34.5-35.5 AOI01-02-SB-14-15 AOI01-02-SB-19-20 AOI01-03-SB-14-15 AOI01-03-SB-22-23 AOI02-01-SB-14-15 AOI02-01-SB-21-22 DAASF-01-SB-14-15 DAASF-01-SB-31-32 DAASF-02-SB-14-15 DAASF-02-SB-34-35 DAASF-SB-FD1

AOI01-02 AOI01-03 AOI01-03 AOI02-01 AOI02-01 DAASF-01 DAASF-01

Area of Interest 

Location ID AOI01-01 AOI01-01 AOI01-02 DAASF-02 DAASF-02 DAASF-02 DAASF-03 DAASF-03

Perfluoroundecanoic acid (PFUnA)

6:2 Fluorotelomer sulfonate (6:2 FTS)

8:2 Fluorotelomer sulfonate (8:2 FTS)

N-ethyl perfluorooctanesulfonamidoacetic acid (NEtFOSAA)

N-methyl perfluorooctanesulfonamidoacetic acid (NMeFOSAA)

Perfluorobutanesulfonic acid (PFBS)

Perfluorobutanoic acid (PFBA)

Perfluorodecanesulfonic acid (PFDS)

Perfluorodecanoic acid (PFDA)

Perfluorododecanoic acid (PFDoA)

Perfluoroheptanesulfonic acid (PFHpS)

Perfluoroheptanoic acid (PFHpA)

Perfluorohexanesulfonic acid (PFHxS)

Perfluorohexanoic acid (PFHxA)

Perfluorononanesulfonic acid (PFNS)

Perfluorononanoic acid (PFNA)

Perfluorooctanesulfonamide (PFOSA)

Perfluorooctanesulfonic acid (PFOS)

Perfluorooctanoic acid (PFOA)

Perfluoropentanesulfonic acid (PFPS)

Perfluoropentanoic acid (PFPA)

Perfluorotetradecanoic acid (PFTeDA)

Perfluorotridecanoic acid (PFTriDA)

Perfluoroundecanoic acid (PFUnA)

4:2 Fluorotelomer sulfonate (4:2 FTS) 
Table 6-4 - PFAS Detections in Groundwater

Duncan Readiness Center and Army Aviation Support Facility, Delaware

Analyte Screening 

Level 1 Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual Result LOD LOQ Qual

 PFAS (ng/L)

- < 1.1 2.1 U < 0.95 1.9 U < 1.0 2.0 U < 1.2 2.3 U < 1.0 2.0 U < 0.97 1.9 U < 1.0 2.0 U

- < 4.3 5.4 U < 3.8 4.8 U < 4.0 5.0 U 2.9 4.6 5.8 J < 4.1 5.1 U < 3.9 4.9 U < 4.0 5.0 U

- < 2.1 3.2 U < 1.9 2.9 U < 2.0 3.0 U < 2.3 3.5 U < 2.0 3.1 U < 1.9 2.9 U < 2.0 3.0 U

- < 1.1 3.2 U < 0.95 2.9 U < 1.0 3.0 U < 1.2 3.5 U < 1.0 3.1 U < 0.97 2.9 U < 1.0 3.0 U

- < 1.3 2.1 U < 1.1 1.9 U < 1.2 2.0 U < 1.4 2.3 U < 1.2 2.0 U < 1.2 1.9 U < 1.2 2.0 U

600 8.0 1.1 2.1 2.1 0.95 1.9 8.6 1.0 2.0 3.5 1.2 2.3 1.2 1.0 2.0 J 1.2 0.97 1.9 J 29 1.0 2.0

- 96 4.3 5.4 18 3.8 4.8 29 4.0 5.0 140 4.6 5.8 40 4.1 5.1 39 3.9 4.9 120 4.0 5.0

- < 1.1 2.1 U < 0.95 1.9 U < 1.0 2.0 U < 1.2 2.3 U < 1.0 2.0 U < 0.97 1.9 U < 1.0 2.0 U

- 0.87 1.1 2.1 J 7.9 0.95 1.9 < 1.0 2.0 U < 1.2 2.3 U < 1.0 2.0 U < 0.97 1.9 U < 1.0 2.0 U

- < 1.1 2.1 U < 0.95 1.9 U < 1.0 2.0 U < 1.2 2.3 U < 1.0 2.0 U < 0.97 1.9 U < 1.0 2.0 U

- 1.7 1.1 2.1 J 1.6 0.95 1.9 J 1.5 1.0 2.0 J 0.98 1.2 2.3 J < 1.0 2.0 U < 0.97 1.9 U < 1.0 2.0 U

- 87 1.1 2.1 15 0.95 1.9 27 1.0 2.0 190 1.2 2.3 19 1.0 2.0 19 0.97 1.9 89 1.0 2.0

- 170 1.1 2.1 25 0.95 1.9 89 1.0 2.0 14 1.2 2.3 11 1.0 2.0 11 0.97 1.9 320 1.0 2.0

- 98 1.1 2.1 22 0.95 1.9 38 1.0 2.0 280 1.2 2.3 36 1.0 2.0 34 0.97 1.9 140 1.0 2.0

- < 1.1 2.1 U < 0.95 1.9 U < 1.0 2.0 U < 1.2 2.3 U < 1.0 2.0 U < 0.97 1.9 U < 1.0 2.0 U

- 16 1.1 2.1 35 0.95 1.9 8.0 1.0 2.0 5.4 1.2 2.3 0.57 1.0 2.0 J 0.54 0.97 1.9 J < 1.0 2.0 U

Perfluorooctanesulfonamide (PFOSA) - 1.0 1.1 2.1 J 1.9 0.95 1.9 J+ 2.4 1.0 2.0 < 1.2 2.3 U < 1.0 2.0 U 2.3 0.97 1.9 < 1.0 2.0 U

Perfluorooctanesulfonic acid (PFOS) 40 32 1.1 2.1 150 0.95 1.9 75 1.0 2.0 5.7 1.2 2.3 J+ < 1.0 2.0 U < 0.97 1.9 U 2.4 1.0 2.0 J+

Perfluorooctanoic acid (PFOA) 40 120 1.1 2.1 23 0.95 1.9 36 1.0 2.0 230 1.2 2.3 29 1.0 2.0 27 0.97 1.9 150 1.0 2.0

- 9.6 1.1 2.1 1.9 0.95 1.9 15 1.0 2.0 1.1 1.2 2.3 J 0.80 1.0 2.0 J 0.82 0.97 1.9 J 42 1.0 2.0

- 97 1.1 2.1 18 0.95 1.9 28 1.0 2.0 290 1.2 2.3 31 1.0 2.0 30 0.97 1.9 130 1.0 2.0

- < 1.1 2.1 U < 0.95 1.9 U < 1.0 2.0 U < 1.2 2.3 U < 1.0 2.0 U < 0.97 1.9 U < 1.0 2.0 U

- < 1.1 2.1 U < 0.95 1.9 U < 1.0 2.0 U < 1.2 2.3 U < 1.0 2.0 U < 0.97 1.9 U < 1.0 2.0 U

- < 1.1 2.1 U < 0.95 1.9 U < 1.0 2.0 U < 1.2 2.3 U < 1.0 2.0 U < 0.97 1.9 U < 1.0 2.0 U

Notes

J = Estimated concentration

J+ = Estimated concentration, bias high.

U = The analyte was not detected at a level greater than or equal to the adjusted detection limit (DL)

ng/L = Nanogram(s) per liter

(1) Deputy Assistant Secretary of Defense. 2019. Risk Based Screening Levels Calculated for PFOS, PFOA, PFBS in Groundwater using USEPA’s RSL Calculator with HQ=0.1 (Deputy Assistant Secretary of Defense, 2021).

Values exceeding the Screening Level are shaded gray

LOD = Limit of Detection

LOQ = Limit of Quantitation

Qual = Qualifier

< = analyte not detected above the LOD

- = No screening level

Location ID

Sample Name

Parent Sample ID

Sample Date

AOI01-01

AOI01-01-GW

6/3/2021

AOI01-02

AOI01-02-GW

6/3/2021

AOI01-03

AOI01-03-GW

6/3/2021

AOI02-01

AOI02-01-GW

6/3/2021

DAASF-01

DAASF-01-GW

6/3/2021

DAASF-01

DAASF-GW-FD

DAASF-01-GW-06032021

6/3/2021

DAASF-02

DAASF-02-GW

6/3/2021

6:2 Fluorotelomer sulfonate (6:2 FTS)

Perfluorobutanesulfonic acid (PFBS)

4:2 Fluorotelomer sulfonate (4:2 FTS) 

8:2 Fluorotelomer sulfonate (8:2 FTS)

N-methyl perfluorooctanesulfonamidoacetic acid (NMeFOSAA)

N-ethyl perfluorooctanesulfonamidoacetic acid (NEtFOSAA)

Perfluorodecanesulfonic acid (PFDS)

Perfluorodecanoic acid (PFDA)

Perfluorododecanoic acid (PFDoA)

Perfluoroheptanesulfonic acid (PFHpS)

Perfluoroheptanoic acid (PFHpA)

Perfluorohexanesulfonic acid (PFHxS)

Perfluorohexanoic acid (PFHxA)

Perfluorononanesulfonic acid (PFNS)

Perfluorononanoic acid (PFNA)

Perfluorobutanoic acid (PFBA)

Perfluoropentanesulfonic acid (PFPS)

Perfluoropentanoic acid (PFPA)

Perfluorotetradecanoic acid (PFTeDA)

Perfluorotridecanoic acid (PFTriDA)

Perfluoroundecanoic acid (PFUnA)
Table 6-4 - PFAS Detections in Groundwater

Duncan Readiness Center and Army Aviation Support Facility, Delaware

Result LOD LOQ Qual Result LOD LOQ Qual

55 1.0 2.0 12 0.88 1.8

1100 40 50 310 35 44

< 2.0 3.0 U < 1.8 2.6 U

< 1.0 3.0 U < 0.88 2.6 U

< 1.2 2.0 U < 1.1 1.8 U

7.0 1.0 2.0 3.5 0.88 1.8

190 4.0 5.0 130 3.5 4.4

< 1.0 2.0 U < 0.88 1.8 U

< 1.0 2.0 U < 0.88 1.8 U

< 1.0 2.0 U < 0.88 1.8 U

5.4 1.0 2.0 3.3 0.88 1.8

180 1.0 2.0 110 0.88 1.8

130 1.0 2.0 43 0.88 1.8

400 1.0 2.0 230 0.88 1.8

< 1.0 2.0 U < 0.88 1.8 U

4.6 1.0 2.0 4.1 0.88 1.8

1.4 1.0 2.0 J < 0.88 1.8 U

12 1.0 2.0 J+ 37 0.88 1.8

280 1.0 2.0 100 0.88 1.8

6.0 1.0 2.0 3.6 0.88 1.8

520 10 20 250 0.88 1.8

< 1.0 2.0 U < 0.88 1.8 U

< 1.0 2.0 U < 0.88 1.8 U

< 1.0 2.0 U < 0.88 1.8 U

MW15-GW

MW15-GW

6/3/2021

DAASF-03

DAASF-03-GW

6/3/2021

Notes

J = Estimated concentration

J+ = Estimated concentration, bias high.

U = The analyte was not detected at a level greater than or equal to the adjusted detection limit (DL)

ng/L = Nanogram(s) per liter

(1) Deputy Assistant Secretary of Defense. 2019. Risk Based Screening Levels Calculated for PFOS, PFOA, PFBS in Groundwater using USEPA’s RSL Calculator with HQ=0.1 (Deputy Assistant Secretary of Defense, 2021).

Values exceeding the Screening Level are shaded gray

LOD = Limit of Detection

LOQ = Limit of Quantitation

Qual = Qualifier

< = analyte not detected above the LOD

- = No screening level

Analyte

Screening 

Level 1

 PFAS (ng/L)

4:2 Fluorotelomer sulfonate -

6:2 Fluorotelomer sulfonate -

8:2 Fluorotelomer sulfonate -

N-ethyl perfluorooctanesulfonamidoacetic acid -

N-methyl perfluorooctanesulfonamidoacetic acid -

Perfluorobutanesulfonic acid (PFBS) 600

Perfluorobutanoic acid -

Perfluorodecanesulfonic acid -

Perfluorodecanoic acid -

Perfluorododecanoic acid -

Perfluoroheptanesulfonic acid -

Perfluoroheptanoic acid -

Perfluorohexanesulfonic acid -

Perfluorohexanoic acid -

Perfluorononanesulfonic acid -

Perfluorononanoic acid -

Perfluorooctanesulfonamide (PFOSA) -

Perfluorooctanesulfonic acid (PFOS) 40

Perfluorooctanoic acid (PFOA) 40

Perfluoropentanesulfonic acid -

Perfluoropentanoic acid -

Perfluorotetradecanoic acid -

Perfluorotridecanoic acid -

Perfluoroundecanoic acid -

Location ID

Sample Name

Parent Sample ID

Sample Date
Army National Guard Site Inspections

Site Inspection Report

Duncan RC and AASF, Delaware

Figure 6-1

PFOS Detections in Soil (AOI 1 and AOI 2)

MW-15

DAASF-03

DAASF-02

DAASF-01

AOI02-01

AOI01-03

AOI01-02

AOI01-HA-04 AOI01-01

AOI01-HA-05

AOI01-HA-03

AOI01-HA-06

AOI01-HA-02

AOI01-HA-01

MW-15

DAASF-03

DAASF-02

DAASF-01

AOI02-01

AOI01-03

AOI01-02

AOI01-01

MW-15

DAASF-03

DAASF-02

DAASF-01

AOI02-01

AOI01-03

AOI01-02

AOI01-01

3

0 200

Feet

Facility Data

Facility Boundary

Area of Interest

Potential PFAS Release

Hydrology/Hydrogeology

Groundwater Flow Direction

Surface Water Flow Direction

Retention Pond

Wetlands

DE

^_

Data Sources:

ESRI 2020

AECOM 2020

Date:.......................March 2022

Prepared By:.............................EA

Prepared For:....................USACE

Projection:.......WGS 84 UTM 18N

Path: \\lovetongis\GISdata\Federal\Nationwide\PFAS\MAES_634250383\PROJECTS\SIReport\DuncanArmory\DuncanArmory.aprx

0 200

Feet

0 200

Feet > 1,600

>ND - 10

10 - 130

130 - 1,600

PFOS Results (μg/Kg)

ND (Non-detect)

> 1,600

>ND - 10

10 - 130

130 - 1,600

PFOS Results (μg/Kg)

ND (Non-detect)

> 1,600

>ND - 10

10 - 130

130 - 1,600

PFOS Results (μg/Kg)

ND (Non-detect)

Shallow Intermediate Deep
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Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 6-12

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Army National Guard Site Inspections

Site Inspection Report

Duncan RC and AASF, Delaware

Figure 6-2

PFOA Detections in Soil (AOI 1 and AOI 2)

MW-15

DAASF-03

DAASF-02

DAASF-01

AOI02-01

AOI01-03

AOI01-02

AOI01-01 AOI01-HA-04

AOI01-HA-05

AOI01-HA-03

AOI01-HA-06

AOI01-HA-02

AOI01-HA-01

MW-15

DAASF-03

DAASF-02

DAASF-01

AOI02-01

AOI01-03

AOI01-02

AOI01-01

MW-15

DAASF-03

DAASF-02

DAASF-01

AOI02-01

AOI01-03

AOI01-02

AOI01-01

3

0 200

Feet

Facility Data

Facility Boundary

Area of Interest

Potential PFAS Release

Hydrology/Hydrogeology

Surface Water Flow Direction

Groundwater Flow Direction

Retention Pond

Wetlands

DE

^_

Data Sources:

ESRI 2020

AECOM 2020

Path: \\lovetongis\GISdata\Federal\Nationwide\PFAS\MAES_634250383\PROJECTS\SIReport\DuncanArmory\DuncanArmory.aprx

0 200

Feet

0 200

Feet

Shallow Intermediate Deep

> 1,600

>ND - 10

10 - 130

130 - 1,600

PFOA Results (μg/Kg)

ND (Non-detect)

> 1,600

>ND - 10

10 - 130

130 - 1,600

PFOA Results (μg/Kg)

ND (Non-detect)

> 1,600

>ND - 10

10 - 130

130 - 1,600

PFOA Results (μg/Kg)

ND (Non-detect)

Date:.......................March 2022

Prepared By:.............................EA

Prepared For:....................USACE

Projection:.......WGS 84 UTM 18N
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 6-14

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Army National Guard Site Inspections

Site Inspection Report

Duncan RC and AASF, Delaware

Figure 6-3

PFBS Detections in Soil (AOI 1 and AOI 2)

MW-15

DAASF-03

DAASF-02

DAASF-01

AOI02-01

AOI01-03

AOI01-02

AOI01-01 AOI01-HA-04

AOI01-HA-05

AOI01-HA-03

AOI01-HA-06

AOI01-HA-02

AOI01-HA-01

MW-15

DAASF-03

DAASF-02

DAASF-01

AOI02-01

AOI01-03

AOI01-02

AOI01-01

MW-15

DAASF-03

DAASF-02

DAASF-01

AOI02-01

AOI01-03

AOI01-02

AOI01-01

3

0 200

Feet

Facility Data

Facility Boundary

Area of Interest

Potential PFAS Release

Hydrology/Hydrogeology

Surface Water Flow Direction

Groundwater Flow Direction

Retention Pond

Wetlands

DE

^_

Data Sources:

ESRI 2020

AECOM 2020

Path: \\lovetongis\GISdata\Federal\Nationwide\PFAS\MAES_634250383\PROJECTS\SIReport\DuncanArmory\DuncanArmory.aprx

0 200

Feet

0 200

Feet

Shallow Intermediate Deep

> 25,000

ND (Non-detect)

>ND - 100

100 - 900

1,900 - 25,000

PFBS Results (μg/Kg)

> 25,000

ND (Non-detect)

>ND - 100

100 - 900

1,900 - 25,000

PFBS Results (μg/Kg)

> 25,000

ND (Non-detect)

>ND - 100

100 - 900

1,900 - 25,000

PFBS Results (μg/Kg)

Date:.......................March 2022

Prepared By:.............................EA

Prepared For:....................USACE

Projection:.......WGS 84 UTM 18N
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 6-16

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Army National Guard Site Inspections

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Duncan RC and AASF, Delaware

Figure 6-4

PFOA, PFOS and PFBS Detections in Groundwater (AOI 1 and AOI 2)

MW-15

DAASF-03

DAASF-02

DAASF-01

AOI02-01

AOI01-03

AOI01-02

AOI01-01

MW-15

DAASF-03

DAASF-02

DAASF-01

AOI02-01

AOI01-03

AOI01-02

AOI01-01

3

0 200

Feet

Facility Data

Facility Boundary

Area of Interest

Potential PFAS Release

Hydrology/Hydrogeology

Surface Water Flow Direction

Groundwater Flow Direction

Retention Pond

Wetlands

DE

^_

Data Sources:

ESRI 2020

AECOM 2020

Path: \\lovetongis\GISdata\Federal\Nationwide\PFAS\MAES_634250383\PROJECTS\SIReport\DuncanArmory\DuncanArmory.aprx

0 200

Feet

> 400

>ND - 10

10 - 40

40 - 70

70 - 400

PFOA Results (ng/L)

ND (Non-detect)

> 400

>ND - 10

10 - 40

40 - 70

70 - 400

PFOS Results (ng/L)

ND (Non-detect)

PFOA PFOS

MW-15

DAASF-03

DAASF-02

DAASF-01

AOI02-01

AOI01-03

AOI01-02

AOI01-01

0 200

Feet

> 1,000

ND (Non-detect)

>ND - 100

100 - 600

600 - 1,000

PFBS Results (ng/L)

PFBS

Date:.......................March 2022

Prepared By:.............................EA

Prepared For:....................USACE

Projection:.......WGS 84 UTM 18N
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 6-18

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Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 7-1

7. EXPOSURE PATHWAYS

The CSMs for each AOI, revised based on the SI findings, are presented on Figure 7-1. A CSM 

presents the current understanding of the site conditions with respect to known and suspected 

sources, potential transport mechanisms and migration pathways, and potentially exposed human 

receptors. A human exposure pathway is considered potentially complete when the following 

conditions are present: 

1. Contaminant source;

2. Environmental fate and transport;

3. Exposure point;

4. Exposure route; and

5. Potentially exposed populations.

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

circle symbol to represent an incomplete exposure pathway. Areas with no identified complete 

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

complete if PFOA, PFOS, or PFBS are detected, in which case the CSM figure uses a half-filled 

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

filled circle symbol is used to indicate when a potentially complete exposure pathway has 

detections of PFOA, PFOS, or PFBS above the SLs. Areas with an identified potentially 

complete pathway and a complete pathway may warrant further investigation. 

In general, the potential PFAS exposure pathways are ingestion and inhalation. Human exposure 

via the dermal contact pathway may occur, and current risk practice suggests it is an insignificant 

pathway compared to ingestion; however, exposure data for dermal pathways are sparse and 

continue to be the subject of PFAS toxicological study. The receptors evaluated are consistent 

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

include site workers (e.g., facility staff and visiting soldiers), construction workers, off-facility 

residents, and trespassers (though unlikely due to restricted access). The CSM for AOIs 1 and 2, 

revised based on the SI findings, are presented on Figure 7-1 and Figure 7-2. 

7.1 SOIL EXPOSURE PATHWAY 

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

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

aforementioned criteria. 

7.1.1 AOI 1 – Helicopter Crash Site

AFFF was potentially released in one area associated with AOI 1 when an ARNG helicopter 

crashed on the boundary between the facility and the New Castle Airport property. PFOA and 

PFOS were detected in soil at low levels at nine boring locations completed at AOI 1, confirming 

a potential release of PFAS to soil at AOI 1. Based on the results of the SI in AOI 1, grounddisturbing activities to surface soil could result in site worker, construction worker, and 

trespasser exposure to PFOA and PFOS via inhalation of dust and ingestion of surface soil. 

Ground-disturbing activities to subsurface soil could result in construction worker exposure to 
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 7-2

PFOS via ingestion. Therefore, the exposure pathways for inhalation and ingestion are 

potentially complete for these receptors. The CSM is presented in Figure 7-1. 

7.1.2 AOI 2 – Hangar 

AOI 2 encompasses the facility hangar. The hangar fire suppression system currently contains a 

Jet-X 2% high expansion foam concentrate system, the contents of which are not disclosed. 

While there is no known release at this location, firsthand interviewee knowledge only extends 

back to 1991. PFOA and PFOS were detected in one boring location at AOI 2 at low levels 

within the surface and shallow subsurface soil, confirming a potential release of PFAS to soil at 

AOI 2. Based on the results of the SI in AOI 2, ground-disturbing activities to surface soil could 

result in site worker and construction worker exposure to PFOA and PFOS via inhalation of dust. 

Therefore, the exposure pathways for inhalation and ingestion are potentially complete for these 

receptors. The CSM is presented in Figure 7-2. 

7.2 GROUNDWATER EXPOSURE PATHWAY

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

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

based on the aforementioned criteria. 

7.2.1 AOI 1 – Helicopter Crash Site

PFOA, PFOS and PFBS were detected in groundwater from all three temporary wells. PFOA 

exceeded the SL at one temporary well location (AOI01-01) and PFOS exceeded the SL at two 

temporary well locations (AOI01-02 and AOI01-03). Domestic, private wells are located less 

than 1 mile downgradient of the facility, the closest of which is located approximately 1,500 ft 

north of the facility boundary; however, the depth of the well and source aquifer are unknown. 

Based on this information, the ingestion exposure pathway is potentially complete for off-facility 

residents. The ingestion exposure pathway for construction workers was deemed incomplete due 

to the depth of groundwater underlying the facility (up to 35 ft bgs), and the likelihood that 

trenching activities would not reach those depths. The CSM is presented in Figure 7-1. 

7.2.2 AOI 2 – Hangar 

PFOA, PFOS, and PFBS were detected in groundwater from the temporary well associated with 

AOI 2, with the PFOA concentration exceeding the SL. Domestic, private wells are located less 

than 1 mile downgradient of the facility, the closest of which is located approximately 1,500 ft 

north of the facility boundary; however, the depth of the well and source aquifer are unknown. 

Based on this information, the ingestion exposure pathway is potentially complete for off-facility 

residents. The ingestion exposure pathway for construction workers was deemed incomplete due 

to the depth of groundwater underlying the facility (up to 35 ft bgs), and the likelihood that 

trenching activities would not reach those depths. The CSM is presented in Figure 7-2. 
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 7-3

7.3 SURFACE WATER AND SEDIMENT EXPOSURE PATHWAY 

The ingestion exposure pathways for surface water and sediment are potentially complete for site 

workers, construction workers, and trespassers based on the surface soil concentrations found in 

the facility detention ponds. PFAS are water soluble and can migrate readily from soil to surface 

water through migration of sediment via storm flow. Additionally, regional shallow groundwater 

flow within the area is inferred to flow towards the Christina River. Therefore, the ingestion 

exposure pathways for surface water and sediment are also potentially complete for recreational 

users of the Christina River. Surface water and sediment were not sampled as part of this SI, as 

the scope of sampling was limited to the presence or absence of PFOS, PFOA, and PFBS in soil 

and groundwater within the facility boundary. 
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 7-4

This page intentionally left blank 
Notes:

1. The resident and recreational users refer to

off-site receptors.

2. Dermal contact exposure pathway is

incomplete for PFAS. Figure 7-1

Conceptual Site Model

AOI 1 Duncan RC and AASF

RECEPTOR

Human Receptors:

Current/Future

Site 

Worker

Construction 

Worker Resident1

Site 

Worker

Construction 

Worker

Resident1

AOI 1

PFAS in 

Surface 

Soil and 

Paved 

Tarmac

Human 

Activities

Precipitation/

Run-Off

Leaching/

Infiltration

Airborne 

Soil 

Particulate

Surface Soil 

at AOI

Surface 

Water/ 

Sediment

Subsurface 

Soil

Shallow 

Groundwater

Ingestion

Ingestion

Ingestion

Ingestion

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

Emergency 

Response to 

Helicopter 

Crash

SOURCE

Source Release 

Mechanism Media

PATHWAY

Transport

and Migration Media Exposure 

Routes

Inhalation 

of Dust

Potentially Complete Pathway with Exceedance of 

Screening Level

Trespasser/

Recreational 

User1

Trespasser/

Recreational 

User1
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 7-6

This page intentionally left blank 
Notes:

1. The resident and recreational users refer to

off-site receptors.

2. Dermal contact exposure pathway is

incomplete for PFAS. Figure 7-2

Conceptual Site Model

AOI 2 Duncan RC and AASF

RECEPTOR

Human Receptors:

Current/Future

Site 

Worker

Construction 

Worker Resident1 Trespasser/

Recreational 

User1

Site 

Worker

Construction 

Worker

Resident1

AOI 2

PFAS in 

Surface 

Soil and 

Paved 

Tarmac

Human 

Activities

Precipitation/

Run-Off

Leaching/

Infiltration

Airborne 

Soil 

Particulate

Surface Soil 

at AOI

Surface 

Water/ 

Sediment

Subsurface 

Soil

Shallow 

Groundwater

Ingestion

Ingestion

Ingestion

Ingestion

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

Potential 

release of AFFF 

from the hangar 

fire suppression 

system 

SOURCE

Source Release 

Mechanism Media

PATHWAY

Transport

and Migration Media Exposure 

Routes

Inhalation 

of Dust

Potentially Complete Pathway with Exceedance of 

Screening Level

Trespasser/

Recreational 

User1
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 7-8

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Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 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 SUMMARY 

The SI field activities at the facility were conducted on 23 May and on 2 and 3 June 2021. The SI 

field activities included soil and groundwater sampling. Field activities were conducted in 

accordance with the UFP-QAPP Addendum (EA 2021b), except as previously noted in 

Section 5.8. 

To fulfill the project DQOs set forth in the approved SI UFP-QAPP Addendum (EA 2021b), 

samples were collected and analyzed for a subset of 24 PFAS by LC/MS/MS compliant with 

QSM Version 5.3 Table B-15 as follows. The 24 PFAS analyzed as part of the ARNG SI 

program are specified in Section 5.7 of this SI Report. The following sampling was conducted: 

• 30 soil grab samples collected from 13 boring locations (seven soil borings and six

surface soil hand auger locations);

• Eight grab groundwater samples from seven temporary well locations and one existing

facility monitoring well;

The information gathered during this investigation was used to determine PFOA, PFOS, and 

PFBS were present at or above SLs. Additionally, the CSMs were refined to assess whether a 

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

exposure to PFOA, PFOS, and PFBS at the AOIs, which are described in Chapter 7. 

8.2 SI GOALS EVALUATION

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

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

data collected during this investigation. 

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

facility.

PFOA, PFOS, and PFBS were detected at the facility in groundwater, whereas PFOA and

PFOS were detected in soil. PFOA, PFOS, and PFBS were detected both at source areas

as well as near the facility boundary between the source areas and the potential drinking

water receptors. Detections in groundwater exceeded the SLs for PFOA and PFOS.
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 8-1

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

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

environment. 

PFOA, PFOS, and PFBS were detected in groundwater samples associated with both 

AOIs. All four of the groundwater samples collected during the SI exceeded the SLs. 

Therefore, none of the release areas have been eliminated from further consideration.

3. Determine the potential need for a TCRA (applies to drinking water only). The primary 

actions that will be considered include provision of alternative water supplies or 

wellhead treatment.

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

4. Collect or develop data to evaluate the release.

Out of the six surface soil (hand auger) borings and two soil borings samples collected 

across the preferential surface flow pathway leaving the Helicopter Crash Site (AOI 1),

PFOS or PFOA were detected in all surface interval samples. Though these detections 

were low, this may indicate that AFFF migrated along this pathway, collecting in the 

stormwater detention ponds. Similarly, AOI02-01 had detections of PFOS and PFOA in 

the surface interval samples. This may suggest that AFFF was released from the facility 

Hangar fire suppression system or within the surrounding area. Additionally, PFOS or 

PFOA were detected at low levels in the surface interval samples taken along the 

boundary, which may suggest that AFFF was released outside of the Duncan RC and 

AASF property. 

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

an RI (if determined necessary). 

The collected geological data indicate a highly permeable and conductive environment 

with soils dominated by sand and silt, with some interbedded, thin clay lenses. The depth 

to groundwater observed during the SI ranged from approximately 25.9 to 32.9 ft bgs. 

Localized groundwater flow direction under the site is to the northwest. These geologic 

and hydrogeologic observations can be used in development of technical approach for the 

RI. 

6. If PFOA, PFOS, and PFBS are determined to be present, aim to evaluate whether the 

concentrations can be attributed to on-facility or off-facility sources that were identified 

within 4 miles of the installation as part of the PA (e.g., fire stations, major 

manufacturers, other DoD facilities). 

Based upon the qualitative evaluation of soil results in combination with quantitative 

groundwater results and groundwater flow direction analysis, the source of detected 

PFOA, PFOS, and PFBS at AOI 1 is likely the result of AFFF expended by the municipal 

fire department in response to the 1970s helicopter crash; however, PFOA, PFOS, and 
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 8-2

PFBS were detected in temporary wells installed upgradient of AOIs 1 and 2, one of 

which exceeded the SLs in groundwater, suggesting an off-facility source may also be 

impacting the facility. Additionally, PFOA exceeded the SL in the sample taken from the 

temporary well location along the northeastern facility boundary.

8.3 OUTCOME

Based on the CSMs developed and revised based on the SI findings, there is potential for 

exposure to residential drinking water receptors from potential releases of AFFF at the Duncan 

RC and AASF, and potentially from off-facility sources.

Sample chemical analytical concentrations collected during this SI were compared against the 

project SLs for PFOA, PFOS, and PFBS in soil and groundwater, as described in Table 6-1. The 

following bullets summarize the SI results: 

• AOI 1 − PFOS or PFOA were detected in groundwater at concentrations exceeding the 

individual SLs of 40 nanograms per liter (ng/L) in all temporary well locations associated 

with AOI 1, with maximum concentrations of PFOS at 150 ng/L and PFOA at 120 ng/L

at locations AOI01-02 and AOI01-01, respectively. PFBS was detected in groundwater at 

AOI 1, but did not exceed the SL.

• AOI 2 − PFOA, PFOS, and PFBS were detected in groundwater at AOI 2. PFOA 

exceeded the SL in groundwater with a concentration of 230 ng/L at AOI02-01. PFOS

and PFBS did not exceed the SLs. 

• AOI 1 and 2 − PFOA and PFOS were detected in soil at both AOI 1 and 2 at low 

concentrations, several orders of magnitude below the SLs. There were no detections of 

PFBS at either AOI. 

• Upgradient Boundary Samples − PFOA, PFOS, and PFBS were detected in groundwater 

upgradient of AOI 1 and AOI 2 in samples taken from locations DAASF-01 and DAASF02. The sample taken from location DAASF-02 exceeded the PFOA SL with a 

concentration of 150 ng/L, but there were no exceedances in the sample taken from 

location DAASF-01. The sample taken from location DAASF-03, located along the 

northeastern facility boundary, also exceeded the SL for PFOA with a concentration of 

280 ng/L.

• Downgradient Boundary Samples - PFOA was detected in groundwater at downgradient 

location MW-15 with a concentration of 100 ng/L, exceeding the SL. PFBS and PFOS 

were detected at this location below their respective SLs. 

• Recommendations − Based on the results of the SI, further evaluation of AOIs 1 and 2

are warranted in a Remedial Investigation.

Table 8-1 summarizes the SI results for soil and groundwater. Based on the CSMs developed 

and revised in light of the SI findings, there is potential for exposure to residential drinking water 
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 8-3

receptors caused by potential DoD activities at the facility as well as potential and known offfacility adjacent sources. 

Table 8-2 summarizes the rationale used to determine if an AOI should be considered for further 

investigation under CERCLA and undergo an RI. Based on the results of this SI, further 

evaluation is warranted in the RI for AOIs 1 and 2: Helicopter Crash Site and Hangar. 
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 8-4

Table 8-1. Summary of Site Inspection Findings

AOI Potential PFAS Release Area

Soil –

Source Area

Groundwater –

Source Area

Groundwater –

Facility Boundary

1 Helicopter Crash Site

2 Hangar

Legend:

 = Detected; exceedance of screening levels.

 = Detected; no exceedance of screening levels.

 = Not detected.

Table 8-2. Site Inspection Recommendations

AOI Description Rationale Future Action

1 Helicopter Crash Site Exceedances of the SLs in 

groundwater at source area. No 

exceedances of SLs in soil.

Proceed to RI

2 Hangar Exceedances of SLs in groundwater 

at source area. No exceedances of 

SLs in soil.

Proceed to RI
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 9-1

9. REFERENCES

AECOM Technical Services., Inc. 2020. Final Preliminary Assessment Report, Duncan Armory 

AASF, New Castle, Delaware. June.

AMEC Foster Wheeler. 2019. Final Report FY16 Phase I Regional Site Inspections for 

Perfluorinated Compounds, Delaware 166th Airlift Wing, Delaware National Guard Base.

Department of the Army (DA). 2016a. EM-200-1-2, Environmental Quality, Technical Project 

Planning Process. 29 February. 

. 2016b. Army Guidance to Address Perfluorooctane Sulfonate (PFOS) and 

Perfluorooctanoic Acid (PFOA) Contamination. August.

. 2018. Army Guidance for Addressing Releases of Per-and Polyfluoroalkyl Substances. 

September.

Deputy Assistant Secretary of Defense. 2021. Investigation Per- and Polyfluoroalkyl Substances 

within The Department of Defense Cleanup Program. U.S. Department of Defense. 

15 September.

Department of Defense (DoD). 2019. General Data Validation Guidelines. November.

. 2020. Data Validation Guidelines Module 3: Data Validation Procedure for Per- and 

Polyfluoroalkyl Substances Analysis by QSM Table B-15. May.

EA Engineering, Science, and Technology, Inc. PBC (EA). 2019. Comprehensive Site Inspection 

Report, New Castle Public Wells Groundwater Plume Site (DE-0363), New Castle, 

Delaware. April. 

. 2020a. Final Programmatic Uniform Federal Policy Quality Assurance Project Plan, 

Site Inspections for Per- and Polyfluoroalkyl Substances Impacted Sites, ARNG Installations, 

Nationwide. December.

. 2020b. Accident Prevention Plan, Programmatic Uniform Federal Policy Quality 

Assurance Project Plan, Site Inspections for Per- and Polyfluoroalkyl Substances impacted 

Sites, ARNG Installations, Nationwide. November.

. 2021a. Accident Prevention Plan / Site Safety and Health Plan Addendum, Site 

Inspections for Per- and Polyfluoroalkyl Substances Impacted Sites, ARNG Installations 

Nationwide, Duncan Readiness Center and Army Aviation Support Facility, Delaware. 

February. 

. 2021b. Final Site Inspection Uniform Federal Policy Quality Assurance Project Plan 

(UFP-QAPP) Addendum, Duncan Readiness Center and Army Aviation Support Facility, 
Site Inspection Report Version: Final

Duncan Readiness Center and Army Aviation Support Facility, Delaware

EA Engineering, Science, and Technology, Inc., PBC 9-2

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