FINAL

Preliminary Assessment Report

Stern Armory,

Wilmington, Delaware

Perfluorooctanesulfonic Acid (PFOS) and Perfluorooctanoic 

Acid (PFOA) Impacted Sites

ARNG Installations, Nationwide

June 2020

Prepared for:

Army National Guard Bureau

111 S. George Mason Drive

Arlington, VA 22204

UNCLASSIFIED
PFAS Preliminary Assessment Report

Stern Armory, Wilmington, Delaware

i

Table of Contents

Executive Summary ....................................................................................................................1

1. Introduction ........................................................................................................................3

Authority and Purpose ..............................................................................................3

Preliminary Assessment Methods .............................................................................3

Report Organization ..................................................................................................4

Facility Location and Description...............................................................................4

Facility Environmental Setting ...................................................................................4

1.5.1 Geology .........................................................................................................5

1.5.2 Hydrogeology .................................................................................................5

1.5.3 Hydrology .......................................................................................................6

1.5.4 Climate ...........................................................................................................6

1.5.5 Current and Future Land Use .........................................................................7

2. Fire Training Areas ...........................................................................................................11

Controlled Burn .......................................................................................................11

3. Non-Fire Training Areas ...................................................................................................13

4. Emergency Response Areas ............................................................................................14

5. Adjacent Sources .............................................................................................................15

Supply Room Fire ...................................................................................................15

Former GM Factory.................................................................................................15

DuPont Facility ........................................................................................................15

Air National Guard Base .........................................................................................15

6. Preliminary Conceptual Site Model ..................................................................................17

7. Conclusions .....................................................................................................................18

Findings ..................................................................................................................18

Uncertainties ...........................................................................................................18

Potential Future Actions ..........................................................................................19

8. References ......................................................................................................................21
PFAS Preliminary Assessment Report

Stern Armory, Wilmington, Delaware

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Figures

Figure ES-1 Summary of Findings

Figure 1-1 Facility Location

Figure 1-2 Groundwater Features

Figure 1-3 Surface Water Features

Figure 2-1 Fire Training Areas

Figure 5-1 Adjacent Sources

Figure 7-1 Summary of Findings

Tables

Table 7-1 No Suspected Release Areas

Table 7-2 Uncertainties

Appendices

Appendix A Data Resources

Appendix B Preliminary Assessment Documentation

B.1 Interview Records

B.2 Visual Site Inspection Checklists

B.3 Conceptual Site Model Information

Appendix C Photographic Log
PFAS Preliminary Assessment Report

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Acronyms and Abbreviations

°F degrees Fahrenheit

AECOM AECOM Technical Services, Inc.

AFFF aqueous film forming foam

AFW Amec Foster Wheeler

amsl Above Mean Sea Level

ANG Air National Guard

AOI Area of Interest

ARNG Army National Guard

bmsl Below Mean Sea Level

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

CFR Code of Federal Regulations

CRA Conestoga-Rovers & Associates

CSM conceptual site model

DEANG Delaware Air National Guard

DEARNG Delaware Army National Guard

DGS Delaware Geological Survey

DNREC Delaware Department of Natural Resources and Environmental Control

DRBC Delaware River Basin Commission

EDRTM Environmental Data Resources, Inc.TM

FMS Field Maintenance Shop

FTA fire training area

GM General Motors

HA Health Advisory

IED Installations & Environment Division

NCCDE New Castle County Delaware Government

PA Preliminary Assessment

PFAS per- and poly-fluoroalkyl substances

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

SI Site Inspection

UCMR3 Unregulated Contaminant Monitoring Rule 3

US United States

USACE United States Army Corps of Engineers

USCB United States Census Bureau

USEPA United States Environmental Protection Agency

USGS United States Geological Survey

VSI visual site inspection
PFAS Preliminary Assessment Report

Stern Armory, Wilmington, Delaware

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Executive Summary

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

Inspections (SIs) for Perfluorooctanesulfonic acid (PFOS) and Perfluorooctanoic acid (PFOA)

Impacted Sites at ARNG Facilities Nationwide. A PA for per- and polyfluoroalkyl substances

(PFAS)-containing materials was completed for Stern Armory (also referred to as the “facility”) in

Wilmington, Delaware, to assess potential PFAS release areas and exposure pathways to

receptors. Stern Armory currently resides on a portion of land deeded to the Delaware ARNG

(DEARNG) in 1971 from the State of Delaware through the Division of Highway and

Transportation. The performance of this PA included the following tasks:

· Reviewed available administrative record documents and Environmental Data Resources,

Inc. (EDR)TM report packages to obtain information relevant to potential PFAS releases, such

as: drinking water well locations, historical aerial photographs, Sanborn maps, and

environmental compliance actions in the area surrounding the facility;

· Conducted a site visit on 5 August 2019 and completed visual site inspections (VSIs) at

locations where PFAS-containing materials were suspected of being stored, used, or

disposed;

· Interviewed current Stern Armory and DEARNG personnel, including environmental

managers and operations staff during the site visit;

· Identified Areas of Interest (AOIs) and developed a preliminary conceptual site model to

summarize potential PFAS source-pathway-receptor linkages for each AOI.

No AOIs related to potential PFAS use, release, or storage were identified at Stern Armory during

the PA (Figure ES-1). Based on facility history and interviews with various personnel, there is no

potential for exposure to PFAS contamination in media at or near the facility.

Based on the US Environmental Protection Agency’s (USEPA) Unregulated Contaminant

Monitoring Rule 3 (UCMR3) data, it was indicated that PFAS were detected in a public water

system above the USEPA’s Health Advisory (HA) within 20 miles of the facility (Appendix A).

PFAS analyses performed in 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.
Former GM

Factory

Controlled

Burn

Supply

Room Fire

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ARNG

GIS BY

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Germantown, MD 20876

Summary of Findings

Base Map: Source: Esri, DigitalGlobe, GeoEye,

Earthstar Geographics, CNES/Airbus DS, USDA, USGS,

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Legend

No Suspected Release

Potential PFAS Release

Facility Boundary

River/Stream

0 250 500 1,000

Feet

2
PFAS Preliminary Assessment Report

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1. Introduction

Authority and Purpose

The Army National Guard (ARNG)-Installations & Environment Division (IED) is the lead agency 

in performing Preliminary Assessments (PAs) and Site Inspections (SIs) for 

Perfluorooctanesulfonic acid (PFOS) and Perfluorooctanoic acid (PFOA) at Impacted Sites at 

ARNG Facilities Nationwide. This work is supported by the United States (US) Army Corps of 

Engineers (USACE) Baltimore District and their contractor AECOM Technical Services, Inc. 

(AECOM) under Contract Number W912DR-12-D-0014, Task Order W912DR17F0192, issued 11 

August 2017. 

The ARNG is assessing potential effects on human health related to processes at facilities that 

used per- and poly-fluoroalkyl substances (PFAS), primarily in the form of aqueous film forming 

foam (AFFF) released as part of firefighting activities, although other PFAS sources are possible. 

In addition, the ARNG is assessing businesses or operations adjacent to the ARNG facility (not 

under the control of ARNG) that could potentially be responsible for a PFAS release. 

PFAS are classified as emerging environmental contaminants that are garnering increasing 

regulatory interest due to their potential risks to human health and the environment. PFAS 

formulations contain highly diverse mixtures of compounds. Thus, the fate of PFAS compounds 

in the environment varies. The regulatory framework at both federal and state levels continues to 

evolve. The US Environmental Protection Agency (USEPA) issued a lifetime Health Advisory (HA) 

for PFOA and PFOS in May 2016, but there are currently no promulgated national standards 

regulating PFAS in drinking water. 

This report presents the findings of a PA for PFAS-containing materials at Stern Armory (also 

referred to as the “facility”) in Wilmington, Delaware, in accordance with the Comprehensive 

Environmental Response, Compensation, and Liability Act (CERCLA), as amended, the National 

Oil and Hazardous Substances Pollution Contingency Plan (40 Code of Federal Regulations 

[CFR] Part 300), and USACE requirements and guidance. 

This PA documents potential locations where PFAS may have been released into the environment 

at Stern Armory. The term PFAS will be used throughout this report to encompass all PFAS 

chemicals being evaluated, including PFOS and PFOA, which are key components of AFFF.

Preliminary Assessment Methods

The performance of this PA included the following tasks: 

· Reviewed available administrative record documents and Environmental Data Resources, 

Inc. (EDR)TM report packages to obtain information relevant to potential PFAS releases, such 

as: drinking water well locations, historical aerial photographs, Sanborn maps, and 

environmental compliance actions in the area surrounding the facility;

· Conducted a site visit on 5 August 2019 and completed visual site inspections (VSIs) at 

locations where PFAS-containing materials were suspected of being stored, used, or 

disposed;

· Interviewed current Stern Armory and Delaware ARNG (DEARNG) personnel including 

environmental managers and operations staff during the site visit;

· Identified Areas of Interest (AOIs) and developed a preliminary conceptual site model (CSM) 

to summarize potential PFAS source-pathway-receptor linkages for each AOI.
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Report Organization

This report has been prepared in accordance with the USEPA Guidance for Performing 

Preliminary Assessments under CERCLA (USEPA 1991). The report sections and descriptions of 

each are presented below:

· Section 1 – Introduction: identifies the project purpose and authority and describes the 

facility location, environmental setting, and methods used to complete the PA.

· Section 2 – Fire Training Areas: describes the fire training areas (FTAs) at the facility 

identified during the site visit.

· Section 3 – Non-Fire Training Areas: describes other locations of potential PFAS releases 

at the facility identified during the site visit.

· Section 4 – Emergency Response Areas: describes areas of potential PFAS release at the 

facility, specifically in response to emergency situations.

· Section 5 – Adjacent Sources: describes sources of potential PFAS release adjacent to the 

facility that are not under the control of ARNG. 

· Section 6 – Preliminary Conceptual Site Model: describes the pathways of PFAS transport 

and receptors for the AOIs and the facility.

· Section 7 – Conclusions: summarizes the data findings and presents the conclusions and 

uncertainties of the PA.

· Section 8 – References: provides the references used to develop this document.

· Appendix A – Data Resources

· Appendix B – Preliminary Assessment Documentation

· Appendix C – Photographic Log

Facility Location and Description

Stern Armory occupies approximately 4 acres in Wilmington, Delaware (Figure 1-1). The facility 

is located adjacent to Delcastle Technical High School, with the west side of the facility running 

along the eastern property boundary for the school. Directly across the street from Stern Armory 

is another DEARNG enclave as well as the location of a former General Motors (GM) production 

plant. Wilmington, Delaware is a metropolitan area with a population of approximately 70,000 (US 

Census Bureau [USCB], 2018). Properties surrounding Stern Armory are primarily zoned for 

single-family homes and industrial areas (New Castle County Delaware Government [NCCDE], 

2018).

Stern Armory is home to the DEARNG Recruiting and Retention Battalion. The facility operates 

under a deed enacted in 1971 between the State of Delaware Division of Highway and 

Transportation and the DEARNG. The DEARNG has custodial rights over the tract of land and is 

responsible for its maintenance and upkeep. 

Stern Armory has been used as an active military facility since 1971. Currently and historically, 

the facility has been used for vehicle maintenance and ammunition storage. The facility includes 

an armory, a facility maintenance shop (FMS), and administrative offices. 

Facility Environmental Setting

The facility is located in northern New Castle County, Delaware, between Wilmington and Newark. 

Major geographic features include the Christina River, which flows generally northeast, into the 
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Delaware River, and is part of the Christina River Basin reaching into Pennsylvania (Delaware

Watersheds, n.d.). The Delaware River flows south to the Delaware Bay. Buildings, asphalt, and

concrete cover much of the facility, but small green spaces exist around the parking lot and on

the southwestern corner of the property. Stern Armory lies within the Coastal Plain region of

Delaware and is a predominantly low, flat area about 100 feet above mean sea level (amsl)

(Figure 1-2).

Little environmental work has been performed at Stern Armory. Therefore, information in the

following sections has been drawn primarily from the Remedial Investigation report for the nearby

Delaware Air National Guard (DEANG) in New Castle, Delaware and an environmental

assessment for the nearby former GM facility (Amec Foster Wheeler [AFW], 2019; ConestogaRovers & Associates [CRA], 2010).

1.5.1 Geology

Based on the available data from US Geological Survey (USGS) maps, the facility lies within the

Coastal Plain Delaware Bay Group (USGS, 2005). The Potomac Formation, mostly consisting

of variegated silt and clay with interbedded quartzitic sands, underlies the facility (CRA, 2010).

Soil type within this group, and subsequently within the boundary of the facility, appears to consist

of medium to medium-to-coarse sands above fine-to-medium to fine sandy silt (Figure 1-2). The

sands of this group are primarily quartzose, with varying quantities of feldspar. Deposits in this

group are vertically and laterally heterogeneous, with an upward fining of sediment texture

(Delaware Geological Survey [DGS], 2019).

1.5.2 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. Previous environmental investigations were performed at the GM Facility, located 0.2

miles from Stern Armory, as well as investigations at a DEANG facility 3.5 miles from Stern

Armory. Due to the proximity of these studies, it is inferred that the geologic information provided

is similar to that at Stern Armory. 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. Groundwater around the facility is typically observed at approximately

11 to 13.5 feet below ground surface, or around 66 to 68.5 feet amsl, and flows to the

west/southwest (CRA, 2010).

The Upper Potomac Aquifer lies in both the shallow and intermediate groundwater-bearing zones.

The shallow zone extends from 0 to 30 feet 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 feet

thick, extends approximately 50 feet 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

suggest that the shallow and intermediate zones are interconnected, as they show similar trends.

Groundwater flow in both zones of the Upper Potomac Aquifer as well as the Columbia Aquifer is

generally to the southwest (Figure 1-2).

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 feet thick; it does not vertically transmit

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

while groundwater elevation measurements from deep monitoring wells in the study are

approximately 5 to 10 feet bmsl. These measurements suggest that groundwater of this aquifer

is confined, and there is little transmission of water vertically between the Upper and Middle
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Stern Armory, Wilmington, Delaware

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Potomac Aquifers. Groundwater in the Middle Potomac Aquifer flows to the south-southeast

(Figure 1-2).

In New Castle County, south of the Chesapeake and Delaware Canal and approximately 13 miles

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

private wells. However, north of the canal, in northern New Castle County, groundwater supplies

only 30 percent of drinking water (DGS, 2019). 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 in the area of Stern Armory. The area of contamination is located

2.3 miles south of the facility, and it is approximately 7 square miles and 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. The public water supply is treated for PFAS contamination before

distribution (DNREC, 2019); however, there are two private domestic supply wells and one

potable geothermal recharge well within 1 mile of the facility.

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

that PFAS were detected in a public water system above the HA within 20 miles of the facility

(Appendix A). PFAS analyses performed in 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.

1.5.3 Hydrology

South of Stern Armory 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

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 percent of New Castle County’s water supply, the majority

of which comes from the Christina River Basin, which provides 60 percent of New Castle County’s

water overall (DGS, 2019). The majority of 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 River lies approximately 1

mile west of the facility, and tidal freshwater wetlands occur throughout the area (Delaware

Watersheds, n.d.).

Stern Armory sits on the Lower White Clay Creek Watershed. On the facility, runoff flows away

from the paved areas and structures towards the wooded areas to the northeast and north.

However, surrounding the facility, general surface water flow is south towards the Christina River,

which flows northeast to the Delaware River.

The facility is closest to the 68-mile marker of the Delaware River (Delaware River Basin

Commission [DRBC], 2011). 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 (DRBC, 2012).

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 (DRBC, 2012).

1.5.4 Climate

The climate at Stern Armory is humid continental. The Delaware Bay and Atlantic Ocean to the

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

and summer months. Although the extremes are moderated, the climate at Stern Armory is still

continental, with hot summers, cold winters, and precipitation throughout the year (AFW, 2019).

Mean annual temperature in New Castle is 54 degrees Fahrenheit (°F). The average annual high
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temperature for Wilmington, Delaware in New Castle County, is 64.1°F, and the average annual

low temperature is 45.8°F. Annual precipitation for Wilmington is approximately 43 inches of rain

and 19 inches of snowfall (US Climate Data, 2019).

1.5.5 Current and Future Land Use

Stern Armory currently resides on a portion of land deeded to the DEARNG in 1971 from the State

of Delaware through the Division of Highway and Transportation; it has been an active military

facility since the signing of the lease in October 1971. The facility is currently used as an armory

and ammunition supply space, a vehicle maintenance shop, and for administrative activities.

Future land use is not anticipated to change.
STERN ARMORY

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12420 Milestone Center Drive

Germantown, MD 20876

Facility Location

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

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

Q:\Projects\ENV\GEARS\GEO\ARNG PFAS\900-CAD-GIS\920-GIS or Graphics\MXD\DE\Stern_Armory\Fig_1-1_Stern_Armory_Facility_Location.mxd

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Facility Boundary

^_

0 2,000 4,000 8,000

Feet

8
H yde Run

Little Mill Creek

Chest nut Run

Christina River

Red Clay Creek

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2/12/2020 ­ Figure 1-2

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Germantown, MD 20876

Groundwater Features

Base Map: Source: Esri, DigitalGlobe, GeoEye,

Earthstar Geographics, CNES/Airbus DS, USDA, USGS,

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Legend

Facility Boundary

Water Body

Wetland

River/Stream

Inferred Groundwater Flow

Direction - Shallow Aquifer

Inferred Groundwater Flow

Direction - Deep Aquifer

Geology

Amphibolite

Silt

0 1,000 2,000 4,000

Feet

9
Hy de Run

Chestnut

Run

Lit tle Mill Creek

Christina River

Red Clay Creek

Little Mill

Creek Watershed

Lower Christina

River Watershed

Red Clay

Creek

Watershed

Lower White

Clay Creek

Watershed

White Clay Creek

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Surface Water Features

Base Map: Source: Esri, DigitalGlobe, GeoEye,

Earthstar Geographics, CNES/Airbus DS, USDA, USGS,

Q:\Projects\ENV\GEARS\GEO\ARNG PFAS\900-CAD-GIS\920-GIS or Graphics\MXD\DE\Stern_Armory\Fig_1-3_Stern_Armory_Surface_Water.mxd

Legend

Facility Boundary

Water Body

Wetland

River/Stream

Canal/Ditch

Pipeline

Surface Water Flow Direction

0 1,000 2,000 4,000

Feet

10
PFAS Preliminary Assessment Report

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2. Fire Training Areas

One FTA was identified within Stern Armory during the PA through interviews. This FTA is 

described below and shown on Figure 2-1. 

Controlled Burn

During interviews, personnel indicated that controlled burns historically occurred at Stern Armory 

approximately every 3 years. These burns occurred at a designated location and involved the 

burning of drums with flammable materials (such as gasoline or diesel) for fire training purposes. 

The controlled burns would be extinguished using either water or A/B fire extinguishers. It was 

verified that type A/B fire extinguishers were the only kind to ever be used at the facility. 

Interviewees stated that no AFFF or other PFAS-containing foams were used during any 

controlled burns or fire training activities. Interviewee knowledge dates to at least 1995. The exact 

timeframe of these controlled burns is unknown, but some interviewees stated controlled burns 

have not been conducted at the facility since 1990. Firefighting training logs could not be located 

to verify training type and timeframe.
Controlled

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Fire Training Areas

Base Map: Source: Esri, DigitalGlobe, GeoEye,

Earthstar Geographics, CNES/Airbus DS, USDA, USGS,

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No Suspected Release

Facility Boundary

River/Stream

0 100 200 400

Feet

12
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3. Non-Fire Training Areas

In addition to FTAs, the PA evaluated areas where PFAS-containing materials may have been

broadly used, stored, or disposed. This may include buildings with fire suppression systems, paint

booths, AFFF storage areas, and areas of compliance demonstrations. Information on these

features obtained during the PA are included in Appendices A and B. No non-FTA areas where

AFFF was stored or used were identified during the PA through interviews or historical document

review.
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4. Emergency Response Areas

No emergency response areas were identified within Stern Armory during the PA through

interviews or historical document review. The City of Wilmington Fire Department would handle

any potential fire or emergency response incident at Stern Armory.
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5. Adjacent Sources

Four potential off-facility sources of PFAS located adjacent to Stern Armory, not under the control 

of ARNG, were identified during the PA through interviews and news reports. A description of each 

adjacent source is presented below, and the adjacent sources are shown on Figure 5-1. 

Supply Room Fire

In approximately 2002, a fire broke out in the supply room of the ARNG readiness center, directly 

across the street from Stern Armory. Belvedere Fire Company responded to the fire and 

extinguished the flames with only water; no AFFF or PFAS-containing materials were used to 

suppress the fire. Additionally, all fire suppression systems within the readiness center contain 

only water. 

Historically, an Ansul fire suppression system was present in the kitchen within the readiness 

center. This fire suppression system was inspected annually; however, according to interviews, 

the system was non-PFAS containing, and no known spills or releases occurred from this system 

throughout the duration of its use. 

Former GM Factory

A GM automobile factory was historically located approximately 0.75 miles east of Stern Armory. 

In 2001, a release of approximately 150 gallons of fire-fighting foam was reported at this facility 

(CRA, 2010). An out of service tank was being transported to another location on the facility when 

the tank malfunctioned, and foam was released. This foam was believed to have entered a nearby 

stormwater catch basin. The GM factory contacted the Division of Water Resources shortly after 

to report the incident. 

Additionally, at about the same timeframe, a fire was reported at the GM factory. Several nearby 

emergency response entities helped respond to this incident. It is unknown whether PFAScontaining foam were used for fire suppression during this emergency response incident or during 

the reported spill at the facility; however, given operational activities at the GM factory, the 

requirement for fire suppression, and the number of entities who responded to the emergency 

response incident, there is the potential for the foam released during both of these events to be 

PFAS-containing. 

DuPont Facility

Approximately 3.5 miles northeast of Stern Armory is a DuPont Experimental Station. This facility, 

originally built in 1903, is the first industrial research laboratory in the nation and the largest 

research and development facility of DuPont (DuPont, 2019). While no direct spills or releases of 

PFAS-containing chemicals could be confirmed during interviews or historical document review, 

the entire facility is responsible for researching and developing various goods and materials that 

contain PFAS chemicals. This location has the potential for unintended spills or releases.

Air National Guard Base

The nearby Air National Guard (ANG) base, located 3 miles south-southeast of the facility, has 

undergone an SI for PFAS. Results of the study show HA exceedances for PFAS in groundwater 

and detections in a surface water sample (AFW, 2019). Of the groundwater sample locations, 

eight locations had results above the HA, and one of two surface water sample locations had a 

combined PFOS and PFOA detection of 0.4247 micrograms per liter (μg/L) (AFW, 2019). Due to 

the ANGB’s downgradient location, contamination there is not believed to influence Stern Armory. 
Hyde Run

Chestnut Run

Little Mill Creek

White Clay Creek

Nonesuc h Creek

Alapoc as R un

Brandywine Creek

Christina R iver

Red Clay

Creek

Former GM

Factory

DuPont

Factory

ANGB

Supply

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Germantown, MD 20876

Adjacent Sources

Base Map: Source: Esri, DigitalGlobe, GeoEye,

Earthstar Geographics, CNES/Airbus DS, USDA, USGS,

C:\Users\grace.canham\AECOM Directory\Stankevich, Michael - ARNG_PFAS_GIS_60552172\MXDs\DE\Stern_Armory\Fig_5-1_Stern_Armory_AdjacentSources.mxd

Legend

No Suspected Release

Potential PFAS Release

Facility Boundary

Water Body

Wetland

River/Stream

Canal/Ditch

0 2,000 4,000 8,000

Feet

16
PFAS Preliminary Assessment Report

Stern Armory, Wilmington, Delaware

17

6. Preliminary Conceptual Site Model

Based on the PA findings from interviews with facility personnel, on-facility observations, review

of EDRTM reports, and online research, no release areas were identified as AOIs at Stern Armory.

A CSM identifies three components necessary for potentially complete exposure pathways related

to a site: (1) source, (2) pathway, and (3) receptor. If any of these elements are missing, the

pathway is considered incomplete. However, since no PFAS sources were identified to originate

at Stern Armory or from activities associated with the facility, preliminary CSMs were not

developed.

Nearby adjacent sources were identified during this PA. According to a USEPA Radius Map

Report run in 2019, there are 344 water wells within a 1-mile radius of the facility, with three of

these listed as potable water wells (EDRTM, 2019). Based on actual and potential AFFF releases

at sources adjacent to Stern Armory coupled with fluctuating groundwater and surface water flow

directions, there is the potential for adjacent AFFF releases to impact groundwater and surface

water at Stern Armory.
PFAS Preliminary Assessment Report

Stern Armory, Wilmington, Delaware

18

7. Conclusions

This report presents a summary of available information gathered during the PA on the use of 

AFFF at Stern Armory. The PA findings are based on the information presented in Appendix A

and Appendix B.

Findings

Based on information obtained during interviews conducted with facility personnel, facility 

observations, and reviewed documentation, it is confirmed that AFFF has never been stored, 

used, or released Stern Armory; therefore, no AOIs related to PFAS releases were identified. 

Interviewee knowledge from DEARNG personnel at the facility and from other DEARNG 

personnel dates to at least 1995. Evidence obtained during the PA supports that current or former 

ARNG activities have not contributed to any potential PFAS contamination in media at or near the 

facility. 

The area shown in Table 7-1 and discussed in Section 2 was determined to have no suspected 

release.

Table 7-1 No Suspected Release Areas

No Suspected 

Release Area Used by Rationale for No Suspected Release Determination

Controlled Burn DEARNG

Interviewee knowledge indicates no AFFF was 

ever used, stored, or released during fire training 

activities throughout facility operational history

Adjacent sources of PFAS exist near Stern Armory, including the Former GM Factory and the 

DuPont facility. Potential long-term storage or release of AFFF at these locations could result in 

potential exposure to PFAS in all media at Stern Armory. 

Uncertainties

A number of information sources were investigated during this PA to determine the potential for 

PFAS-containing materials to have been present, used, or released at the facility. Historically, 

documentation of PFAS use was not required because PFAS were considered benign. Therefore, 

records were not typically kept by the facility or available during the PA on the use of PFAS in 

training, firefighting, other non-traditional activities, or on its disposition. 

The conclusions of this PA are based on all available information, including: previous 

environmental reports, EDRsTM, observations made during the VSI, and interviews. Interviews of 

personnel with direct knowledge of a facility generally provided the most useful insights regarding 

a facility's historical and current PFAS-containing materials. Sometimes, the provided information 

was vague. Gathered information has a degree of uncertainty due to the absence of written 

documentation, the limited number of personnel with direct knowledge due to staffing changes, 

the time passed since PFAS were first used (1969 to present), and a reliance on personal 

recollection. Inaccuracies may arise in potential PFAS release locations, dates of release, volume 

of releases, and the concentration of AFFF used. There is also a possibility the PA has missed a 

source of PFAS, as the science of how PFAS may enter the environment continually evolves.

In order to minimize the level of uncertainty, readily available data regarding the use and storage 

of PFAS were reviewed, retired and current personnel were interviewed, multiple persons were 
PFAS Preliminary Assessment Report

Stern Armory, Wilmington, Delaware

19

interviewed for the same potential source area, and potential source areas were visually 

inspected. Table 7-2 summarizes the uncertainties associated with the PA.

Table 7-2 Uncertainties

Location Source of Uncertainty

Former GM Factory

It is unknown whether PFAS-containing chemicals were used, 

stored, or released during the operational history of this facility, 

as well as whether there is an effect on Stern Armory

DuPont Facility

While use and storage of PFAS-containing chemicals can be 

confirmed at this location, dates, quantity, and concentration of 

potential spills or releases at this location are unknown, as 

well as whether there is an effect on Stern Armory 

Controlled Burn

The exact timeframe of fire training at this location could not 

be determined. There is conflicting information on whether fire 

training was conducted with water or A/B fire extinguishers.

General

Activities at Stern Armory are unknown between when the 

property was acquired in 1971 and when interviewee 

knowledge began in 1995.

Potential Future Actions

Based on the absence (1995-present) of the use, storage, or release of PFAS-containing 

materials at Stern Armory, no AOIs were identified during the PA. Evidence does not indicate that 

current or former ARNG activities contributed PFAS contamination in media at or near the facility. 

Stern Armory will not move forward in the CERCLA process. 
Former GM

Factory

Controlled

Burn

Supply

Room Fire

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

GC

VK

12/6/2019

12/6/2019

NOTES Preliminary Assessment for PFAS at Stern Armory, DE

1:6,000

12/6/2019 ­ Figure 7-1

PM RG 12/6/2019

12420 Milestone Center Drive

Germantown, MD 20876

Summary of Findings

Base Map: Source: Esri, DigitalGlobe, GeoEye,

Earthstar Geographics, CNES/Airbus DS, USDA, USGS,

Q:\Projects\ENV\GEARS\GEO\ARNG PFAS\900-CAD-GIS\920-GIS or Graphics\MXD\DE\Stern_Armory\Fig_7-1_Stern_Armory_Summary.mxd

Legend

No Suspected Release

Potential PFAS Release

Facility Boundary

River/Stream

0 250 500 1,000

Feet

20
PFAS Preliminary Assessment Report

Stern Armory, Wilmington, Delaware

21

8. References

Amec Foster Wheeler (AFW). 2019. Final Report FY16 Phase 1 Regional Site Inspections for

Per and Poly Fluoralkyl Substances Volume I of XII.

Conestoga-Rovers & Associates (CRA). 2010. Phase I Environmental Site Assessment: GM

Wilmington Assembly Plant. Prepared for Motors Liquidation Company. (Accessed October

2019).

Delaware Department of Natural Resources and Environmental Control (DNREC). New castle

County Airport Area Community Fact Sheet. (Accessed September 2019).

http://www.dnrec.delaware.gov/dwhs/SIRB/Documents

Delaware Geological Survey (DGS). 2019. Hydrologic Information for Delaware. (Accessed

September 2019). https://www.dgs.udel.edu/water-resources

Delaware Geological Survey (DGS). 2019. Potomac Formation. (Accessed August 2019).

https://www.dgs.udel.edu/delaware-geology/unit/potomac-formation

Delaware Geological Survey (DGS). 2019. Delaware Bay Group. (Accessed October 8, 2019)

https://www.dgs.udel.edu/delaware-geology/unit/delaware-bay-group

Delaware River Basin Commission (DRBC). 2012. Contaminants of Emerging Concern in the

Tidal Delaware River. (Accessed November 1, 2019).

https://www.nj.gov/drbc/library/documents/contaminants-of-emergingconcernAug2013rev.pdf

Delaware River Basin Commission (DRBC). 2011. River Mileage System. (Accessed November

11, 2019). https://www.state.nj.us/drbc/basin/river/

Delaware Watersheds. n.d. Christina River. (Accessed August 2019).

http://delawarewatersheds.org/piedmont/christina-river/

DuPont. 2019. DuPont Wilmington, DE Experimental Station. (Accessed October 2019).

https://www.dupont.com/locations/wilmington-delaware-the-experimental-station.html

EDRTM. 2019. The EDRTM Radius Map Report with GeoCheck. Inquiry number 5765905.9s.

New Castle County Delaware Government (NCCDE). 2018. Zoning Map Index. (Accessed

September 2019). http://zoningmaps.nccde.org/

U.S. Census Bureau (USCB). 2018. American Community Survey 1-Year Estimates, from 2010-

2018. (Accessed November 2019). https://data.census.gov/cedsci/

U.S. Climate Data. 2019. Climate Wilmington – Delaware. (Accessed August 2019).

https://www.usclimatedata.com/climate/wilmington/delaware/united-states/usde0055

U.S. Environmental Protection Agency (USEPA), 1991. Guidance for Performing Preliminary

Assessments under CERCLA. EPA/540/G91/013.

U.S. Geological Survey (USGS). 2005. Geologic Map of New Castle County, Delaware.

(Accessed October 8, 2019). https://www.dgs.udel.edu/datasets/dgs-geologic-map-no-13-

new-castle-county-dataset
PFAS Preliminary Assessment Report

Stern Armory, Wilmington, Delaware

Appendix A

Data Resources
Data Resources will be provided separately on CD. Data Resources for Stern Armory:

Stern Armory Pervious Site Investigations

• Phase 1 Environmental Site Assessment, Conestoga-Rovers & Associates, February 

2010

• Final Report FY16 Phase 1 Regional Site Inspections for Perfluorinated Compounds, 

Amec Foster Wheeler, April 1, 2019

• Delaware Department of Natural Resources and Environmental Control’s New Castle 

County Airport Area Fact Sheet, PFOS/PFOA Detected in Ground Water from New 

Castle Public Wells

Stern Armory Site Background Documents

• UCMR 3 Data

• USGS Geologic Map of New Castle County, Delaware, Kelvin W. Ramsey, 2005

Stern Armory Site Property Documents

• Stern Armory Land Deed, October 5, 1971

Environmental Data Resources Reports

• Certified Sanborn Map Report, Environmental Data Resources, Inc., August 26, 2019

• Aerial Photo Decade Package, Environmental Data Resources, Inc., August 26, 2019

• Historical Aerials Package, Environmental Data Resources, Inc., August 26, 2019

• Radius Map Report with Geocheck, Environmental Data Resources, Inc., August 26, 

2019
PFAS Preliminary Assessment Report

Stern Armory, Wilmington, Delaware

Appendix B

Preliminary Assessment Documentation
PFAS Preliminary Assessment Report

Stern Armory, Wilmington, Delaware

Appendix B.1

Interview Records





PFAS Preliminary Assessment Report

Stern Armory, Wilmington, Delaware

Appendix B.2

Visual Site Inspection Checklists



PFAS Preliminary Assessment Report

Stern Armory, Wilmington, Delaware

Appendix B.3

Conceptual Site Model Information



PFAS Preliminary Assessment Report

Stern Armory, Wilmington, Delaware

Appendix C

Photographic Log
PreliminaryAssessment Report

AECOM

Stern Armory

Perfluorooctane-Sulfonic Acid (PFOS) and 

Perfluorooctanoic Acid (PFOA) Impacted Sites 

ARNG Installations, Nationwide

APPENDIX C – Photographic Log

Army National Guard, Preliminary 

Assessment for PFAS Stern Armory Wilmington, Delaware

Description:

Water deluge fire suppression 

system. 

Photograph No. 1

Description:

Armory Kitchen. No foam hood 

or fire suppression system.

Photograph No. 2
AECOM

Preliminary Assessment Report 

Stern Armory

Perfluorooctane-Sulfonic Acid (PFOS) and 

Perfluorooctanoic Acid (PFOA) Impacted Sites 

ARNG Installations, Nationwide

APPENDIX C – Photographic Log

Army National Guard, Preliminary 

Assessment for PFAS Stern Armory Wilmington, Delaware

Description:

Type AB fire extinguishers 

kept throughout the building.

Photograph No. 3

Description:

Water deluge system control 

box.

Photograph No. 4
AECOM

Preliminary Assessment Report 

Stern Armory

Perfluorooctane-Sulfonic Acid (PFOS) and 

Perfluorooctanoic Acid (PFOA) Impacted Sites 

ARNG Installations, Nationwide

APPENDIX C – Photographic Log

Army National Guard, Preliminary 

Assessment for PFAS Stern Armory Wilmington, Delaware

Description:

Fire department water hookup.

Photograph No. 5

Description:

Floor drain in the facility 

garage.

Photograph No. 6
AECOM

Preliminary Assessment Report 

Stern Armory

Perfluorooctane-Sulfonic Acid (PFOS) and 

Perfluorooctanoic Acid (PFOA) Impacted Sites 

ARNG Installations, Nationwide

APPENDIX C – Photographic Log

Army National Guard, Preliminary 

Assessment for PFAS Stern Armory Wilmington, Delaware

Description:

Hazmat Shed

Photograph No. 7

Description:

CO2 extinguisher in the 

facility garage.

Photograph No. 8
AECOM

Preliminary Assessment Report 

Stern Armory

Perfluorooctane-Sulfonic Acid (PFOS) and 

Perfluorooctanoic Acid (PFOA) Impacted Sites 

ARNG Installations, Nationwide

APPENDIX C – Photographic Log

Army National Guard, Preliminary 

Assessment for PFAS Stern Armory Wilmington, Delaware

Description:

Location of fire training 

area outside of the facility 

garage.

Photograph No. 9