FINAL

Site Inspection Report 

Grand Prairie Army Aviation 

Support Facility

Grand Prairie, Texas

Perfluorooctanesulfonic Acid (PFOS) and 

Perfluorooctanoic Acid (PFOA) Impacted Sites

ARNG Installations, Nationwide

October 2022

Prepared for:

Army National Guard Bureau

111 S. George Mason Drive

Arlington, VA 22204

UNCLASSIFIED
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Table of Contents

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

3.1.1 Wash Rack ...................................................................................................3-1

3.1.2 Hazardous Materials Storage Building .........................................................3-1

3.1.3 Fuel Station ..................................................................................................3-1

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

3.2.1 Flight Line Ramp ..........................................................................................3-2

3.3 AOI 3.......................................................................................................................3-2

3.3.1 Former Firetruck Location ............................................................................3-2

3.4 Adjacent Sources....................................................................................................3-2

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

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

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

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

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

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

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

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

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

4.6.3 Representativeness......................................................................................4-5

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

4.6.5 Completeness...............................................................................................4-6

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

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

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

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

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

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

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

5.3 Temporary Well Installation and Groundwater Grab Sampling ...............................5-3
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5.4 Synoptic Water Level Measurements .....................................................................5-4

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

5.6 Investigation-Derived Waste ...................................................................................5-4

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

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

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

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

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

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

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

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

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

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

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

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

6.4.3 AOI 2 Conclusions........................................................................................6-3

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

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

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

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

6.6 Facility Boundary ....................................................................................................6-4

6.6.1 Facility Boundary Soil Analytical Results......................................................6-4

6.6.2 Facility Boundary Groundwater Analytical Results .......................................6-5

6.6.3 Facility Boundary Conclusions .....................................................................6-5

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

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

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

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

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

7.1.4 Facility Boundary ..........................................................................................7-2

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

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

7.2.2 AOI 2 ............................................................................................................7-3

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

7.2.4 Facility Boundary ..........................................................................................7-3

7.3 Surface Water and Sediment Exposure Pathway...................................................7-3

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

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

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

8.3 Outcome .................................................................................................................8-3

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

Appendix A Data Validation Reports

Appendix B Field Documentation

B1. Log of Daily Notice of Field Activities

B2. Sampling Forms

B3. Field Change Request Forms

B4. Survey Data

Appendix C Photographic Log

Appendix D TPP Meeting Minutes

Appendix E Boring Logs 

Appendix F Analytical Results

Appendix G Laboratory Reports

Figures

Figure 2-1 Facility Location

Figure 2-2 Facility Topography

Figure 2-3 Groundwater Features

Figure 2-4 Groundwater Elevations Contours, March 2021

Figure 2-5 Surface Water Features

Figure 3-1 Areas of Interest

Figure 5-1 Site Inspection Sample Locations

Figure 6-1 PFOS Detections in Soil

Figure 6-2 PFOA Detections in Soil

Figure 6-3 PFBS Detections in Soil

Figure 6-4 PFOS, PFOA, PFBS Detections in Groundwater

Figure 7-1 Conceptual Site Model, AOI 1

Figure 7-2 Conceptual Site Model, AOI 2

Figure 7-3 Conceptual Site Model, AOI 3

Figure 7-4 Conceptual Site Model, Facility Boundary
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Tables

Table ES-1 Screening Levels (Soil and Groundwater)

Table ES-2 Summary of Site Inspection Findings

Table ES-3 Site Inspection Recommendations

Table 5-1 Site Inspection Samples by Medium

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

Elevations

Table 6-1 Screening Levels (Soil and Groundwater)

Table 6-2 PFAS Detections in Surface Soil

Table 6-3 PFAS Detections in Subsurface Soil

Table 6-4 PFAS Detections in Groundwater

Table 8-1 Summary of Site Inspection Findings

Table 8-2 Site Inspection Recommendations
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Acronyms and Abbreviations

% percent

°F degrees Fahrenheit

μg/kg micrograms per kilogram

6:2 FTS 6:2 Fluorotelomer sulfonic acid

8:2 FTS 8:2 Fluorotelomer sulfonic acid

AECOM AECOM Technical Services, Inc.

AFFF aqueous film forming foam

AOI Area of Interest

ARNG Army National Guard

bgs below ground surface 

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act 

CoC chain of custody

CSM conceptual site model

DA Department of the Army

DNAS Dallas Naval Air Station

DoD Department of Defense

DPT direct push technology

DQI data quality indicator

DQO data quality objective

EIS extraction internal standards

ELAP Environmental Laboratory Accreditation Program

FedEx Federal Express

GPF Grand Prairie Facility

GPRS Ground Penetrating Radar Systems, LLC

HA Health Advisory

HDPE high-density polyethylene 

IDW investigation-derived waste

IIS injection internal standards

ITRC Interstate Technology Regulatory Council

LC/MS/MS liquid chromatography with tandem mass spectrometry

LCS laboratory control spike

LCSD laboratory control spike duplicate

LOD limit of detection

LOQ limit of quantitation

MDL method detection limit

MS matrix spike

MSD matrix spike duplicate

NELAP National Environmental Laboratory Accreditation Program

NEtFOSAA N-ethyl perfluorooctanesulfonamidoacetic acid

ng/L nanograms per liter

NMeFOSAA N-methyl perfluorooctanesulfonamidoacetic acid

OMS organizational maintenance shop

OSD Office of the Secretary of Defense
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OWS oil-water separator

PA Preliminary Assessment

PFAS per- and polyfluoroalkyl substances

PFBA perfluorobutyrate

PFBS perfluorobutanesulfonic acid

PFDA perfluorodecanoic acid

PFDoA perfluoroheptanoic acid

PFHpA perfluoroheptanoic acid

PFHxA perfluorohexanoic acid

PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

PFPeA perfluoropentanoic acid

PFTeDA perfluorotetradecanoic acid

PFTrDA perfluorotridecanoic acid

PFUdA perfluoroundecanoic acid

PID photoionization detector

PQAPP Programmatic QAPP

PVC polyvinyl chloride

QA quality assurance

QAPP Quality Assurance Project Plan

QC quality control

QSM Quality Systems Manual

RI Remedial Investigation

RPD relative percent differences

SI Site Inspection

SL screening level

SOP standard operating procedure

TCEQ Texas Commission on Environmental Quality

TCRA Time Critical Removal Action

TOC total organic carbon

TPP Technical Project Planning

TXARNG Texas Army National Guard

UFP Uniform Federal Policy

US United States

USACE United States Army Corps of Engineers

USCS Unified Soil Classification System
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USEPA United States Environmental Protection Agency

USFWS United States Fish and Wildlife Service

WWTP wastewater treatment plant
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Executive Summary

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

Inspections (SIs) at potential 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). A SI was completed 

at Grand Prairie Army Aviation Support Facility (AASF), Texas. The Grand Prairie AASF will also 

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

Grand Prairie AASF, home to the 149th Aviation Regiment of the Texas ARNG (TXARNG), is 

within the southwest portion of the former Dallas Naval Air Station (DNAS), which was 

decommissioned in 1998. The facility is 12 miles southwest of downtown Dallas and is situated 

adjacent to the northwest shore of Mountain Creek Lake, on property that overlaps into the cities 

of Dallas and Grand Prairie, Texas. The current TXARNG facility houses a hangar, a wash rack, 

fuel station, ramp and flight line, a hazardous materials storage building, an organizational 

maintenance shop, and an armory. Current activities at the Grand Prairie AASF include helicopter 

maintenance and training.

During the PA for PFAS, five potential PFAS release areas were identified: the Wash Rack, 

Hazardous Materials Storage Building, Fuel Station, Flight Line Ramp, and Former Location of a 

Firetruck (AECOM, 2020). PFAS-containing aqueous film-forming foam (AFFF) may have been 

released during fire training activities at the Wash Rack and Flight Line Ramp. AFFF was 

previously stored at the Hazardous Materials Storage Building and the Fuel Station and the 

firetruck historically stored on site was equipped with AFFF. The potential PFAS release areas 

were grouped into three Areas of Interest (AOIs), AOI 1, AOI 2, and AOI 3, which were investigated 

during the SI. The SI field activities were conducted from 22 to 24 March 2021 and included the 

collection of soil and groundwater samples. 

To fulfill the project Data Quality Objectives set forth in the approved SI Quality Assurance Project 

Plan Addendum (AECOM, 2021b), samples were collected and analyzed for a subset of 18 PFAS 

by liquid chromatography with tandem mass spectrometry compliant with Quality Systems Manual 

5.3 Table B-15. The 18 PFAS analyzed as part of the ARNG SI program are specified in Section 

5.8 of this Report.

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

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

Secretary of Defense (OSD) dated 15 September 2021 (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 there is a release identified that is likely attributed to ARNG activities, the AOI 

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

apply to three compounds: PFOS, PFOA, and PFBS.

The SLs are presented on Table ES-1 below. All other results presented in this report are 

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

contain or do not contain the 18 PFAS analyzed within the boundaries of the facility.
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Sample chemical analytical concentrations were compared against the project SLs as described 

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

• At AOI 1, PFOA in groundwater at the Wash Rack, Fuel Station, and downgradient of the 

Hazardous Materials Storage Building exceeded the SL of 40 nanograms per liter (ng/L) at

concentrations of 106 ng/L and 94.4 ng/L, at locations AOI01-01 and AOI01-02,

respectively. Based on the results of the SI, further evaluation of AOI 1 is warranted in the 

Remedial Investigation (RI).

• At the facility boundary, PFOA in groundwater near the northeastern boundary exceeded 

the SL of 40 ng/L at a concentration of 369 ng/L at location Grand Prairie Facility (GPF)-01. 

Based on the results of the SI, further evaluation of the northeastern facility boundary is 

warranted in the RI. 

• At AOI 1 and GPF-01, detected concentrations of PFOS and PFBS in groundwater were 

below SLs.

• At AOI 2, AOI 3, and the eastern facility boundary (GPF-02) detected concentrations of 

PFOA, PFOS, and PFBS in groundwater were below SLs. 

• The detected concentrations of PFOA, PFOS, and PFBS in soil at all AOIs were below the 

SLs. 

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

models developed and revised in light of the SI findings, there is potential for exposure to 

receptors on facility caused by DoD activities at or adjacent to the facility.

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

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

is warranted in the RI for AOI 1: Wash Rack, AOI 1: Fuel Station, and Facility Boundary: GPF-01 

area.

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

Analyte

Residential

(Soil)

(μg/kg)a

0-2 feet below 

ground surface 

(bgs)

Industrial/ 

Commercial 

Composite 

Worker

(Soil)

(μg/kg)a

2-15 feet bgs

Tap Water

(Groundwater)

(ng/L)a

PFOA 130 1,600 40

PFOS 130 1,600 40

PFBS 1,900 25,000 600

Notes:

a.) 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.
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Table ES-2: Summary of Site Inspection Findings

AOI Potential PFAS 

Release Area

Soil –

Source Area

Groundwater –

Source Area

Groundwater –

Facility 

Boundary

1

Wash Rack

Hazardous Materials 

Storage Building

N/A N/A

Fuel Station

2 Flight Line Ramp N/A

3 Former Firetruck 

Location

Facility 

Boundary

GPF-01

GPF-02

Legend:

N/A = not applicable 

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected

Table ES-3: Site Inspection Recommendations

AOI Description Rationale Future Action

1

Wash Rack, 

Hazardous 

Materials 

Storage 

Building, and 

Fuel Station

Exceedances of SLs in groundwater at 

source areas. No exceedances of SLs in 

soil. 

Proceed to RI

2 Flight Line 

Ramp

Detections in groundwater but no 

exceedances of SLs. No exceedances of 

SLs in soil.

No further action

3 Former Firetruck 

Location

Detections in groundwater but no 

exceedances of SLs. No exceedances of 

SLs in soil. 

No further action

Facility 

Boundary

GPF-01

(northeastern 

boundary)

Exceedances of SLs in groundwater at 

source areas. No exceedances of SLs in 

soil. 

Proceed to RI

GPF-02

(eastern 

boundary)

Detections in groundwater but no 

exceedances of SLs. No exceedances of 

SLs in soil.

No further action
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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 Perfluorooctanesulfonic acid (PFOS) and Perfluorooctanoic 

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

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

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

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

Prairie Army Aviation Support Facility (AASF), Texas. The Grand Prairie AASF is also referred to 

as the “facility” throughout this document.

The SI project elements were performed in compliance with Comprehensive Environmental 

Response, Compensation, and Liability Act (CERCLA; United States Environmental Protection 

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

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

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

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

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

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

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

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

1.2 SI Purpose

A PA was performed at Grand Prairie AASF (AECOM, 2020) that identified five potential PFAS 

release areas at the facility, which were grouped into three Areas of Interest (AOIs). The objective 

of the SI is to identify whether there has been a release to the environment from the AOIs and 

determine the presence or absence of PFOA, PFOS, and PFBS at or above screening levels 

(SLs).

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

SI has five goals: 

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

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

2. Determine the potential need for a removal action;

3. Collect or develop data to evaluate potential release;

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

Remedial Investigation (RI), if determined necessary; and

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

associated with the Department of Defense (DoD).

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

potential off-facility PFAS sources. 
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2. Facility Background

2.1 Facility Location and Description

Grand Prairie AASF, home to the 149th Aviation Regiment of the Texas ARNG (TXARNG), is 

within the southwest portion of the former Dallas Naval Air Station (DNAS), which was 

decommissioned in 1998. The facility is 12 miles southwest of downtown Dallas and is situated 

adjacent to the northwest shore of Mountain Creek Lake (Figure 2-1), on property that overlaps 

into the cities of Dallas and Grand Prairie, Texas. TXARNG began leasing approximately 40 acres 

of land situated in Dallas County, Texas in 1975. Historically, the DNAS has provided support to 

the Texas Air National Guard, US Army Reserve, TXARNG, and various Navy and Marine groups.

With the exception of TXARNG operations, the majority of military operations ceased at DNAS in 

September 1998, and the air station was put into caretaker status (Tetra Tech NUS, Inc. [TtNUS], 

2001). The current TXARNG facility houses a hangar, a wash rack, fuel station, ramp and flight 

line, a hazardous materials storage building, an organizational maintenance shop (OMS), and an 

armory. The Grand Prairie AASF Hangar does not have an aqueous film forming foam (AFFF) fire 

suppression system. Current activities at the Grand Prairie AASF include helicopter maintenance 

and training.

2.2 Facility Environmental Setting

Grand Prairie AASF is in north-central Texas, approximately 325 miles north of the Gulf of Mexico. 

The facility is situated near the headwaters of the Trinity River that flow in the upper margins of 

the Coastal Plain. The topography of the site is generally level with slopes along borders with 

water surface water bodies (i.e. Cottonwood Bay to the northeast and Cottonwood Creek to the 

southeast) (Figure 2-2).

2.2.1 Geology

The general stratigraphic sequence present throughout the TXARNG facility consists of Holocene 

and Pleistocene alluvial terrace deposits overlaying the Cretaceous Eagle Ford Shale (Figure 2-

3). The upper soil horizons and alluvium have been disturbed locally by industrial development; 

therefore, shallow surface and subsurface soils are composed of fill materials in some areas. The 

lithology of sediments is primarily clay and silty clay. The clays are interspersed with sporadic 

deposits of streambed sand and gravel (Geo-Marine, Inc [GMI], 2002).

Soil borings completed during the SI found poorly-graded and well-graded sand as the dominant 

lithology of unconsolidated sediments below the Grand Prairie AASF. The borings were completed 

at 15 feet below ground surface (bgs). Layers of clay to silty sand were also observed in the boring 

logs at thicknesses ranging from a few inches up to 6 feet. Many of the logs also reported varying 

percentages of gravel included in the sand packages. 

2.2.2 Hydrogeology

The surficial aquifer below the facility is within the alluvium overburden and the weathered portion 

of the underlying shale. This aquifer is heterogeneous and exhibits characteristics of unconfined 

aquifer systems and semi-confined to confined aquifer systems. These two types of aquifer 

systems are interconnected hydraulically to the adjacent water bodies; Mountain Creek Lake, 

Cottonwood Bay, and the Diversion Channel. Groundwater contour elevations are very similar to 

the land surface topography. In the central section of the facility, the potentiometric surface is 

primarily flat. Along the Cottonwood Bay and the Diversion Channel shorelines, the potentiometric 

surface is extremely steep, and along the east portion of the facility, across the flight line toward 
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Mountain Creek Lake, the potentiometric surface is moderately steep. The groundwater primarily 

flows to the west-northwest in the direction of Cottonwood Bay and the Diversion Channel. 

Seepage velocity of the groundwater underlying the facility within the overburden is estimated to 

range from 0.12 to 0.23 foot per day (TtNUS, 2001) (Figure 2-3). 

Shallow groundwater in the alluvial section flows primarily through the semi-confined to confined 

zones and in unconfined zones of sands and clayey sands. Shallow groundwater is estimated to 

be approximately 4 to 9 feet bgs at the facility, as indicated in well reports stored on the Texas 

Water Development Board Submitted Drillers Reports Database. Clay, silty clay, sandy clay, and 

gravelly clay comprise the semi-confined zones that are cut by joints, microfractures, partings, 

and other zones of macroporosity. The confined zones may be interconnected with the weathered 

and jointed upper surface of the Eagle Ford Shale. The surficial aquifer underlying the facility is 

most likely recharged by the downward migration of rainwater through the vadose zone. Direction 

of groundwater flow was determined from potentiometric surface maps developed from static 

water level data collected during five separate water level gauging events (TtNUS, 2001).

The facility’s drinking water is supplied by the City of Grand Prairie. A query of the Texas Water 

Development Board Submitted Drillers Reports Database identified 21 public supply wells, 17 

domestic wells, 13 irrigation wells, and 19 industrial water supply wells within a 4-mile radius of 

the facility. The public supply wells range in depth from 432 to 1158 feet bgs. The domestic wells 

range in depth from 80 to 1060 feet bgs, the irrigation wells range from 142 to 1165 feet bgs, and 

industrial water supply wells range in depth from 142 to 2,148 feet bgs. The shallowest of the 

wells is the 80-foot-deep domestic well, which is located approximately 4 miles north-northwest 

of the facility. Based on the USEPA’s Unregulated Contaminant Monitoring Rule 3 (UCMR3) data,

no PFAS were detected in a public water system above the USEPA Health Advisory (HA) level 

within 20 miles of the facility (USEPA, 2017a). The HA is 70 nanograms per liter (ng/L) for PFOA 

and PFOS, individually or combined. 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.

Depths to water measured in March 2021 during the SI ranged from 2.67 to 13.08 feet bgs. 

Groundwater elevation contours from the SI are presented on Figure 2-4. Based on depths to 

water measured during the SI, the groundwater flow direction is northward in the direction of 

Cottonwood Bay and westward in the direction of the Diversion Channel.

2.2.3 Hydrology

Surface water in the vicinity of Grand Prairie AASF flows primarily across paved or grassy areas 

and into the storm drainage system that discharges into Cottonwood Bay, the Diversion Channel, 

and Mountain Creek Lake (Figure 2-5). Mountain Creek Lake drains to the northeast from the 

spillway located approximately 1.5 miles east of the facility (TtNUS, 2001). 

2.2.4 Climate

The Dallas-Fort Worth climate is humid subtropical with hot summers. The climate is also 

continental, characterized by a wide annual temperature range. Precipitation also varies 

considerably, ranging from less than 20 to more than 50 inches. Average annual precipitation for 

the facility is 37.35 inches. Winters are mild, but northers occur about three times each month 

and often are accompanied by sudden drops in temperature. The highest temperatures of 

summer are associated with fair skies, westerly winds and low humidity. Characteristically, hot 

spells in summer are broken into three- to five-day periods by thunderstorm activity. There are 

only a few nights each summer when the low temperature exceeds 80 degrees Fahrenheit (oF). 

Summer daytime temperatures frequently exceed 100°F. Average yearly minimum and maximum 

temperatures are 36.5°F and 96.2°F, respectively, with an average annual temperature of 66.6°F. 
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Throughout the year, rainfall occurs more frequently during the night. Usually, periods of rainy 

weather last for only a day or two and are followed by several days with fair skies. A large part of 

the annual precipitation results from thunderstorm activity, with occasional heavy rainfall over brief 

periods of time. Thunderstorms occur throughout the year but are most frequent in the spring 

(National Oceanic and Atmospheric Administration, 2019).

2.2.5 Current and Future Land Use

The Grand Prairie AASF currently includes a hangar, a wash rack, fuel station, ramp and flight 

line, a hazardous materials storage building, an OMS, and an armory. Current land use in the 

direct vicinity of the Grand Prairie AASF includes residential to the west, industrial to the north, as 

well as open areas and parks, commercial and retail buildings, and governmental institutions. A 

representative from the Texas Military Department noted plans to move the Grand Prairie AASF 

to the Naval Air Station Joint Reserve Base Fort Worth soon. Additionally, in August 2020, the City 

of Dallas announced plans to convert the former Dallas Naval Air Station (including the Grand 

Prairie AASF) into low, medium, and high density residential and business use as part of the 

Hensley Field Master Redevelopment Plan (City of Dallas, 2020).

2.2.6 Sensitive Habitat and Threatened/ Endangered Species 

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

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

Service [USFWS], 2021). 

• Birds: 

• Red knot, Calidris canutus rufa (threatened)

• Bald eagle, Haliaeetus leucocephalus (recovery)

• Least tern, Sterna antillarum (recovery)

• Piping Plover, Charadrius melodus (threatened)

• Golden-cheeked warbler, Dendroica chrysopari (endangered)

• Black-capped Vireo, Vireo atricapilla (recovery)

• Whooping crane, Grus americana (endangered)

• Clams: Texas heelsplitter, Potamilus amphichaenus (under review); Texas fawnsfoot,

Truncilla macrodon (candidate)

• Insects: Monarch butterfly, Danaus plexippus (candidate)

• Reptiles: Western Chicken turtle, Deirochelys reticularia ssp. Miaria (under review)

2.3 History of PFAS Use

Five potential PFAS release areas were identified at the Grand Prairie AASF during the PA where 

AFFF may have been used or released historically (AECOM, 2020). Grand Prairie AASF includes 

a Wash Rack, Hazardous Materials Storage Building, Fuel Station, Flight Line Ramp, and a 

Former Firetruck Location. Between 2000 and 2012, AFFF was used during fire training activities 

at the Wash Rack and Flight Line Ramp. AFFF was previously stored at the Hazardous Materials 

Storage Building and the Fuel Station and the firetruck historically stored on site was equipped 

with AFFF. Although there were no reports of known releases from these storage locations, it is 

possible that spills occurred that were not reported.
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 2-4

Historical operations at Grand Prairie AASF have also included training at the Peace Prairie 

Hangar, located northeast of the current TXARNG facility boundary. The Peace Prairie Hangar 

has an AFFF fire suppression system which had an accidental release in 2003. The details of this 

release are included along with the descriptions of AOIs in Section 3. 
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Germantown, MD 20876

Facility Location

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

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

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Legend

Approximate Facility

Boundary per TX ARNG

DNAS Boundary

0 0.5 1 2

Miles

^_

Grand Prairie AASF

AECOM 2-5
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Germantown, MD 20876

Facility Topography

Base Map: USGS The National Map: National

Boundaries Dataset, 3DEP Elevation Program,

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Legend

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Boundary per TX ARNG

0 175 350 700

Feet

AECOM 2-6
!5!5 !5

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12420 Milestone Center Drive

Germantown, MD 20876

Groundwater Features

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

and the GIS User Community

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Approximate Facility

Boundary per TX ARNG

Water Body

Wetland

River/Stream

Canal/Ditch

Pipeline

Groundwater Flow Direction

Geology

Alluvium

Fluvial Terrace Deposits

Austin Chalk

Eagle Ford Group

Woodine Formation

Wells

!P Domestic Well

A! Monitor Well

!5 Irrigation Well

!5 Industrial Well

&<

Historic Observation Well

!C( Public Supply Well

0 0.75 1.5 3

Miles

AECOM 2-7
!?

!?

!?

!?

!?

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AOI01-01

469.94

AOI01-02

468.32

AOI02-01

471.68

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470.49

GPF-01

462.6

GPF-02

474.93

Cottonwood

Bay

Diversion Channel

464

462

466

470

468

472

470

468

474

474

472

464

466

462

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12420 Milestone Center Drive

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Groundwater Elevation Contours

March 2021

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

Geographics, CNES/Airbus DS, USDA, USGS,

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0 165 330 660

Feet

Legend

!? Soil Boring/Temporary

Monitoring Well

Approximate Facility

Boundary per TX ARNG

Water Body

Groundwater elevation

contour

Dashed where inferred

Groundwater Flow Direction

AECOM 2-8
Delaware Creek-West

Fork Trinity

River Watershed

Cottonwood

Creek-Mountain Creek

Lake Watershed

Mountain

Creek Lake

West Fork Trinity River

CottonwoodCreek

Cottonwood Bay

Diversion Channel

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Surface Water Features

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

Geographics, CNES/Airbus DS, USDA, USGS,

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0 0.25 0.5 1

Miles

Legend

Approximate Facility

Boundary per TX ARNG

Water Body

River/Stream

Surface Water Flow

Direction

AECOM 2-9
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Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 2-10

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Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 3-1

3. Summary of Areas of Interest

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

findings, five potential PFAS release areas, Wash Rack, Hazardous Materials Storage Building, 

Fuel Station, Flight Line Ramp, and Former Firetruck Location were identified at Grand Prairie 

AASF and grouped into three AOIs (AECOM, 2020). The potential PFAS release areas are shown 

on Figure 3-1. 

3.1 AOI 1 

AOI 1 consists of three potential PFAS release areas, as described below. 

3.1.1 Wash Rack

AFFF was used during fire training from 2000 to 2012 at the Wash Rack. An unknown quantity of 

AFFF was released during these fire training events. Releases at the Wash Rack would have 

been conveyed to the drain and oil-water separator (OWS), and then depending on the positioning 

of a diverter valve, either flowed to the sanitary sewer system, and ultimately discharged to the 

municipal wastewater treatment plant (WWTP) or flowed to the street. The water discharged to 

the street may have infiltrated to the subsurface near the end of the discharge pipe, as well as 

flowed to the street and ultimately discharged to Cottonwood Bay. The position of the diverter 

valve during AFFF use at the Wash rack is unknown. Based on the nature of the release (during 

maintenance/routine testing), it appears unlikely AFFF would have been discharged to the ground 

surface outside of the Wash Rack, except potentially via runoff to the grassy areas surrounding 

the Wash Rack. PFAS contamination may have infiltrated to subsurface soil via leaks in drains, 

OWS or underground wastewater conveyance piping beneath the wash rack, or leaks along 

piping from the facility to the municipal WWTP. 

3.1.2 Hazardous Materials Storage Building

The Hazardous Materials Storage Building historically housed 30 5-gallon sealed buckets of 3

percent (%) AFFF until 2012. Although there were no known releases of AFFF at the storage 

building, it is possible that spills occurred in the area. AFFF spills in the storage building would 

have most likely been washed to the nearby Wash Rack for disposal. 

3.1.3 Fuel Station

Tri-MaxTM units containing AFFF were stationed at the Fuel Station. Although there were no 

reports of Tri-MaxTM use at the Fuel Station, it is possible that a spill occurred in the area without 

being reported. AFFF spills in the Fuel Station area would most likely infiltrate into the surrounding 

soil. 

Additionally, potential PFAS contamination from AOI 1 may have further infiltrated to shallow 

groundwater, which is flows northward in the direction of Cottonwood Bay and westward in the 

direction of the Diversion Channel.

3.2 AOI 2 

AOI 2 consists of one potential PFAS release area, as described below.
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Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 3-2

3.2.1 Flight Line Ramp

AFFF was used during fire training from 2000 to 2012 at the flight line ramp. An unknown quantity 

of AFFF was released during these fire training events. Based on the nature of the release it 

appears unlikely AFFF would have been discharged to the ground surface outside of the Flight 

Line Ramp, except potentially via runoff to the grassy areas to the southeast of the ramp. PFAS 

contamination may have further infiltrated to subsurface soil in the grassy areas in the vicinity of 

the Flight Line Ramp. Potential PFAS contamination may have further infiltrated to shallow 

groundwater, which flows northward in the direction of Cottonwood Bay and westward in the 

direction of the Diversion Channel.

3.3 AOI 3 

AOI 3 consists of one potential PFAS release area, as described below. 

3.3.1 Former Firetruck Location

The firetruck that was historically located on site was equipped with AFFF. Based on interviews 

no AFFF was ever deployed from the firetruck; however, it is possible that spills occurred in that 

location that were not recorded. AFFF spills in the Former Firetruck Location would have infiltrated 

into soil. Based on the nature of the possible release, PFAS contamination may have further 

infiltrated to subsurface soil through precipitation from rain events. Potential PFAS contamination 

may have further infiltrated to shallow groundwater, which flows northward in the direction of 

Cottonwood Bay and westward in the direction of the Diversion Channel. 

3.4 Adjacent Sources

Sources located adjacent to the Grande Prairie AASF that could have contributed potential PFAS 

releases are described below. 

The Peace Prairie Hangar was built in 1976 and was initially owned and operated by the 

TXARNG. Singapore Air Force troops were trained at the Peace Prairie facility by TXARNG 

personnel. In 1998, the Peace Prairie Hangar was expanded, and an AFFF fire suppression 

system was added. The Peace Prairie Hangar is located northeast of the Grand Prairie AASF. 

Based on interviews, the suppression system has not been triggered, and no leaks have been 

detected since 2013. The system is currently inspected once a month and has been inspected 

monthly since 2015. The Peace Prairie Hangar is no longer part of the TXARNG lease and is 

currently owned by the City of Dallas. 

In 2003, a release was reported from the AFFF fire suppression system at the Peace Prairie 

Hangar. According to the TXARNG Environmental Spill Report, less than 150 gallons of 

ChemguardTM Standard Grade 3% AFFF was released in the Peace Prairie Hangar on 5 May 

2003. The accidental release was caused by a malfunction of the pull station due to vibration, 

triggering the fire suppression system. Once the system was triggered, the 3% AFFF chemical 

mixed with water to produce approximately 5,000 gallons of liquid and 15,000 gallons of foam that 

filled the hangar. Facility personnel washed the liquid/foam mixture into the floor drain, which is 

connected to holding sumps and an OWS. Eagle Construction and Environmental was contracted 

to put the foam/water and any other liquid in the sumps and the OWS into holding pods in case 

of rain, awaiting lab results and then disposal. Some AFFF was released to the ground because 

of a defective diverter valve. Approximately 20,000 gallons of liquid and residue were removed by 

Eagle Construction who transported the wastewater to Cold Springs Processing for disposal.
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 3-3

The Peace Prairie Division had Tri-MaxTM units, which hangar maintenance personnel inspected. 

Peace Prairie personnel reported training monthly with Tri-MaxTM units. It is unknown where this 

training occurred, but it most likely occurred at the Peace Prairie Wash Rack. AFFF concentrate 

is stored in the Peace Prairie Hangar and in the Peace Prairie Bulk Storage Facility. Tri-MaxTM

units were serviced by a contractor, and it is not clear what happened to the old solution. 
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Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 3-4

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!5

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!5 !5

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Historic Location 

of Firetruck

Ramp

Fuel Station Hazardous Materials

Storage Building

Wash Rack Peace Prairie Hangar

with AFFF Fire

Suppression System

Peace Prairie

Hangar OWS

Peace Prairie

Wash Rack

Cottonwood

Creek-Mountain Creek

Lake Watershed

Mountain

Creek Lake

Cottonwood

Bay

Cottonwood Creek

Diversion Channel

AOI 2

AOI 1

AOI 3

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12420 Milestone Center Drive

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Areas of Interest

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

Geographics, CNES/Airbus DS, USDA, USGS,

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0 400 800 1,600

Feet

Legend

Area of Interest

Potential PFAS Release

Approximate Facility

Boundary per TX ARNG

Water Body

River/Stream

Surface Water Flow

Direction

Groundwater Flow Direction

!5 Industrial Well

A! Monitor Well

AECOM 3-5
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AECOM 3-6

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Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 4-1

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 project decision-making

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

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

4.1 Problem Statement

The following problem statement was developed during project planning:

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

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

environmental contaminants that are garnering increasing regulatory interest due to their potential 

risks to human health and the environment. The regulatory framework for managing PFAS at both 

the federal and state level continues to evolve. 

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

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

Defense (OSD) dated 15 September 2021 (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, the AOI

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

originally applied to three compounds: PFOS, PFOA, and PFBS. 

The SLs are presented in Section 6.1 of this Report.

The following quotes from the DA policy documents form the basis for this project (DA, 2016; DA, 

2018): 

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

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

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

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

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

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

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

suppressants, shall be considered possible source areas.”

• “Based on a review of 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.”

• “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; USEPA, 2016b).

4.2 Goals of the Study

The following goals were established for this SI:

1. Determine the presence or absence of PFOA, PFOS, and PFBS at or above SLs.
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Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 4-2

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

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

3. Determine the potential need for a Time Critical Removal Action (TCRA) (applies to 

drinking water only). The primary actions that will be considered include provision of 

alternative water supplies or wellhead treatment.

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

of a RI (if determined necessary).

5. 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).

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

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

4.3 Information Inputs

Primary information inputs included:

• The PA for Grand Prairie AASF (AECOM, 2020);

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

with the site-specific Uniform Federal Policy (UFP)-Quality Assurance Project Plan (QAPP)

Addendum (AECOM, 2021b); and

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

parameters measured at the time of sampling.

4.4 Study Boundaries

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

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

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

owner(s).

4.5 Analytical Approach

Samples were analyzed by Pace Analytical Gulf Coast, accredited under the DoD Environmental 

Laboratory Accreditation Program (DoD ELAP; Accreditation Number 74960) and the National 

Environmental Laboratory Accreditation Program (NELAP; Certificate Number 01955). Data were 

compared to applicable SLs and decision rules as defined in the SI QAPP Addendum (AECOM, 

2021b). These rules governed response actions based on the results of the SI sampling effort.

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

based on the following:

Groundwater:

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

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

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 4-3

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

and downgradient of the potential release areas?

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

receptor?

Soil:

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

bgs)?

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

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

Soil and groundwater samples were collected from each of the potential release areas. 

Groundwater was encountered at approximately 2.67 to 13.08 feet bgs. 

4.6 Data Usability Assessment

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

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

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

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

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

of the right type, quality, and quantity to support the decision-making (DoD, 2019a; DoD, 2019b; 

USEPA, 2017b). 

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

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

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

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

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

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

explanations for all qualified data in greater detail.

4.6.1 Precision

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

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

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

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

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

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

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

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

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

sample EIS recoveries were within the project established precision limits presented in the SI 

QAPP Addendum (AECOM, 2021b). 

Injection internal standards (IIS) were added by the laboratory after sample extraction and prior 

to analysis as a requirement of DoD Quality Systems Manual (QSM) 5.3 to measure relative 

responses of target analytes. Several field and laboratory samples displayed IIS area counts 

outside of quality control (QC) limits. PFAS analytes are not quantitated based on IIS recoveries 
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 4-4

in non-drinking water matrices. No data quality impact is anticipated, and the associated field 

sample results are usable as reported.

LCS/laboratory control spike duplicate (LCSD) pairs were prepared by addition of known 

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

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

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

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

Addendum (AECOM, 2021b).

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

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

for the matrix being tested with limited exceptions. MS/MSD samples were submitted to the 

laboratory for analysis at a rate of 5%. The MS/MSD samples were within the project established 

precision limits presented in the SI QAPP Addendum (AECOM, 2021b) with the exception of the 

PFOA result for AOI01-01-GW and four PFAS compounds for AOI01-01-SB-00-02 which 

displayed percent recoveries greater than the upper QC limit. The positive associated parent 

sample results were qualified “J+” with a likely high bias so these results are likely conservative 

high estimates.

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

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

PFAS and general chemistry parameters. The field duplicates AOI01-01-GW and AOI01-01-SB03-05 displayed precision anomalies for PFNA and PFUnDA, respectively: the field duplicate pairs 

displayed positive results in the parent sample and non-detect results in the associated duplicate 

sample. The positive field duplicate results were qualified “J”, while the non-detect results were 

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

4.6.2 Accuracy

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

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

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

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

surrogates.

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

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

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

preparation and analysis. One LCS/LCSD performed displayed a percent recovery greater than 

the upper QC limits for PFNA and PFTrDA. The associated field sample results were non-detect; 

therefore, no data qualifying action was required, and the associated parent sample results should 

be considered usable as reported. 

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

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

exception. Several MSDs displayed percent recoveries greater than the upper QC limit of 70% 

for multiple target analytes. The positive field sample result associated with the positive biases 

was qualified “J+” and should be considered usable as an estimated value with a positive bias.

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

calibrated analytes were within established QC criteria. The calibration verifications performed 

during the laboratory analyses were within the project established precision limits presented in 

the SI QAPP Addendum (AECOM, 2021b), with one exception. One instrument calibration 
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Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 4-5

sensitivity standard associated recovered above the QC limits for several target analytes. The 

associated field sample results were non-detect and no impact on the data is anticipated.

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 liquid chromatography with tandem mass spectrometry (LC/MS/MS) 

Compliant with QSM 5.3 Table B-15, including the specific preparation requirements (i.e. ENVICarb 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.

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

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

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

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

standard methods in accordance with the SI QAPP Addendum (AECOM, 2021b) for all analyses.

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

control. Multiple instrument and method blanks displayed concentrations for target analytes 

greater than the detection limit. The positive field sample results less than five times the detections 

found in the method and laboratory blanks were qualified “U”, and the associated numerical value 

reported was elevated to the limit of detection (LOD). These results are usable as qualified and 

should be considered false positives.

Equipment blanks and field blanks were also collected for groundwater and soil samples. Several 

field and equipment blanks displayed concentrations of target analytes greater than the LOD. The 

associated field sample results were either non-detect or displayed results greater than five times 

the concentration displayed in the blanks. No data qualifying action was necessary, and the field

sample results should be considered usable as reported.

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

field effort. The drill rig decontamination sample displayed a concentration above the detection 

limit for several target analytes. The associated field sample results were treated as true positives 

by the project team. 

Field samples were extracted and analyzed within the appropriate holding time in order to 

qualitatively express the degree to which data accurately reflect site conditions with limited 

exceptions. The holding time for pH analysis is “immediate”, all field samples analyzed for pH 

were qualified “J” and should be considered usable as estimated values. 

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

usable data were obtained to meet the objectives of the SI and to complete the risk assessment.

4.6.4 Comparability

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

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

analytical methods, units of reporting, and site selection procedures help ensure comparability. 
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AECOM 4-6

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, if applicable: 

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

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

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

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

4.6.6 Sensitivity

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

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

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

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

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

sensitivity and project LOQs specified in the SI QAPP Addendum (AECOM, 2021b). The 

laboratory provided the requested MDL studies and provided applicable calibration standards at 

the LOQ. In order to achieve the DQOs for sensitivity outlined in the SI QAPP Addendum 

(AECOM, 2021b), the laboratory reported all field sample results at the lowest possible dilution. 

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

qualified “J” as estimated values by the laboratory.
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AECOM 5-1

5. Site Inspection Activities

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

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

in accordance with the following approved documents:

• Final Site Inspection Programmatic UFP-Quality Assurance Project Plan (PQAPP) dated 

March 2018 (AECOM, 2018a);

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

• Final Preliminary Assessment Report, Grand Prairie Army Aviation Support Facility, Grand 

Prairie, Texas dated July 2020 (AECOM, 2020);

• Final Site Safety and Health Plan, Grand Prairie Army Aviation Support Facility, Grand 

Prairie, Texas March 2021 (AECOM, 2021a); and

• Final Site Inspection UFP-Quality Assurance Project Plan Addendum, Grand Prairie Army 

Aviation Support Facility, Grand Prairie, Texas dated April 2021 (AECOM, 2021b).

The SI field activities were conducted from 22 to 24 March 2021 and consisted of utility clearance,

direct push boring, soil sample collection, temporary monitoring well installation, grab groundwater 

sample collection, and land surveying. Field activities were conducted in accordance with the SI 

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

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

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

• 18 soil samples from 6 boring locations;

• 6 grab groundwater samples from 6 temporary well locations; and

• 10 quality assurance (QA) samples.

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

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

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

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

is provided in Appendix B3, and land survey data is provided in Appendix B4. Additionally, a 

photographic log of field activities is provided in Appendix C.

5.1 Pre-Investigation Activities

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

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

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

5.1.1 Technical Project Planning

The USACE TPP Process, EM 200-1-2 (USACE, 2016) defines four phases to project planning: 

1.) defining the project phase; 2.) determining data needs; 3.) developing data collection 

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

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

qualitative DQOs, and formulating a sampling approach to address the AOIs identified in the PA. 
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AECOM 5-2

A combined TPP Meeting 1 and 2 was held on 19 November 2020, prior to SI field activities. The 

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

stakeholders for this SI include the ARNG, Texas Army National Guard (TXARNG), USACE, Texas 

Commission on Environmental Quality (TCEQ), and representatives familiar with the facility, the

regulations, and the community. Stakeholders were provided the opportunity to make comments 

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

outcome of the combined TPP Meeting 1 and 2 was memorialized in the SI QAPP Addendum 

(AECOM, 2021b). 

A TPP Meeting 3 will be held after the field event to discuss the results of the SI. Meeting minutes 

for TPP 3 are included in Appendix D of this report. Future TPP meetings will provide an 

opportunity to discuss the results and findings, and future actions, where warranted. 

5.1.2 Utility Clearance

AECOM’s drilling subcontractor, WEST Drilling placed a ticket with the Texas811 utility clearance 

provider to notify them of intrusive work on 16 April 2021. However, because the AASF is a private 

facility, the participating Texas811 locators did not clear utilities at the entire facility. Therefore, 

AECOM contracted Ground Penetrating Radar Systems, LLC (GPRS), a private utility location 

service, to perform utility clearance. GPRS performed utility clearance of the proposed boring 

locations on 23 March 2021 with input from the AECOM field team and Grand Prairie AASF facility 

staff. General locating services and ground-penetrating radar were used to complete the 

clearance. Additionally, the first 5 feet of each boring were pre-cleared 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 

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

potable water source at Grand Prairie AASF was collected on 20 January 2021, prior to 

mobilization, and analyzed for PFAS by LC/MS/MS compliant with QSM 5.3 Table B-15. The 

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

results is presented in Section 4.6.3. 

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

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

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

QAPP Addendum (AECOM, 2021b). Prior to the start of field work each day, a PFAS Sampling 

Checklist was completed as an additional layer of control. The checklist served as a daily reminder 

to each field team member regarding the allowable materials within the sampling environment. 

5.2 Soil Borings and Soil Sampling

Soil samples were collected via direct push technology (DPT), in accordance with the SI QAPP 

Addendum (AECOM, 2021b). A GeoProbe® 7822DT dual-tube sampling system was used to 

collect continuous soil cores to the target depth. A hand auger was used to collect soil from the 

top five feet of the boring, in accordance with AECOM utility clearance procedures. The soil boring 

locations are shown on Figure 5-1 and depths are provided Table 5-1. 

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

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

approximately 2 feet above the groundwater table, and one subsurface soil sample at the midpoint between the surface and the groundwater table. 
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AECOM 5-3

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

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

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

and measurements were recorded on sampling forms (Appendix B2) and in a non-treated field 

logbook (i.e., composition notebook). Depth interval, recovery thickness, PID concentrations, 

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

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

Soil borings completed during the SI found poorly-graded and well-graded sand as the dominant

lithology of unconsolidated sediments below the Grand Prairie AASF. The borings were completed 

at 15 feet bgs. Layers of clay to silty sand were also observed in the boring logs at thicknesses 

ranging from a few inches up to 6 feet. Many of the logs also reported varying percentages of 

gravel included in the sand packages. 

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

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

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

to the laboratory and analyzed for PFAS (LC/MS/MS compliant with QSM 5.3 Table B-15), TOC 

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

Addendum (AECOM, 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, equipment rinsate blank

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 in 

accordance with the SI QAPP Addendum (AECOM, 2021b) using bentonite chips at completion 

of sampling activities. With the exception of AOI02-01, borings were installed in grass areas to 

avoid disturbing concrete or asphalt surfaces.

5.3 Temporary Well Installation and Groundwater Grab Sampling

Temporary wells were installed using a GeoProbe® 7822DT dual-tube sampling system. Once 

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

was constructed of a 5 or 10-foot section (depending on depth to water) of 1-inch Schedule 40 

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

and screen were used to avoid cross contamination between locations. The screen intervals for 

the temporary wells are provided in Table 5-2.

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

samples. After the recharge period, groundwater samples were collected using a peristaltic pump 

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

HDPE bottles and labeled using a PFAS-free marker or pen. The temporary wells were purged at 

a rate determined in the field to reduce turbidity and draw down prior to sampling. Water quality 

parameters (e.g., temperature, specific conductance, pH, dissolved oxygen [DO], and oxidationreduction potential [ORP]) were measured using a water quality meter and recorded on the field 

sampling form (Appendix B2) after each grab sample was collected. Additionally, a subsample 

of each groundwater sample was collected in a separate container, and a shaker test was 

completed to identify if there were any foaming. No foaming was noted in any of the groundwater 

samples.
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AECOM 5-4

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

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

standard CoC procedures to the laboratory and analyzed for PFAS by LC/MS/MS compliant with 

QSM 5.3 Table B-15 in accordance with the SI QAPP Addendum (AECOM, 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. One field reagent blank was collected in 

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

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

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

by removing the PVC and backfilling the hole with bentonite chips. Where possible, temporary 

wells were installed in grass areas to avoid disturbing concrete or asphalt. AOI02-01 was the only 

boring installed in an asphalt area. After the boring was abandoned, the asphalt was repaired with 

cold patch asphalt. 

5.4 Synoptic Water Level Measurements

A synoptic groundwater gauging event was performed between 22 March and 24 March 2021. 

Groundwater elevation measurements were collected from the 6 new temporary monitoring wells. 

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

flow contour map is provided in Figure 2-4. Groundwater elevation data is provided in Table 5-2. 

5.5 Surveying 

The eastern side of each well casing was surveyed by Texas-licensed land surveyors following 

guidelines provided in the SOPs provided in the SI QAPP Addendum (AECOM, 2021b). Survey 

data from the newly installed wells on the facility were collected on 24 March 2021 in the 

applicable Universal Transverse Mercator zone projection with World Geodetic System 84 datum

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

provided in Appendix B4. 

5.6 Investigation-Derived Waste

As of the date of this report, the disposal of 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 SI QAPP Addendum (AECOM, 2021b) and with the DA

Guidance for Addressing Releases of PFAS, Q18 (DA, 2018). 

Soil IDW (i.e., soil cuttings) generated during the SI were containerized in a properly labeled 55-

gallon drum and stored in front of the Hazardous Waste Storage Building at Grand Prairie AASF. 

ARNG will manage disposal of the solid IDW and will coordinate with TXARNG to ensure proper 

disposal in accordance with the DA Guidance for Addressing releases of PFAS, Q18 (DA, 2018).

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

containerized in properly labeled 55-gallon drums and stored in front of the Hazardous Waste 

Storage Building at Grand Prairie AASF. The liquid IDW will not be sampled and will assume PFAS 

characteristics of the associated groundwater samples collected from the source locations. ARNG 

will manage and dispose of the liquid IDW under a separate contract in accordance with SOP No. 

042A for treating Liquid Investigation-Derived Material (purge water, drilling water, and 

decontamination fluids) (EA Engineering, Science, and Technology, Inc., 2021). ARNG will further 

coordinate with TCEQ to ensure proper disposal and the DA Guidance for Addressing Releases 

of PFAS, Q18 (DA, 2018). 
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AECOM 5-5

Other solids such as spent PPE, plastic sheeting, tubing, rope, unused monitoring well 

construction materials, and other environmental media generated during the field activities were 

disposed of at a licensed solid waste landfill.

5.7 Laboratory Analytical Methods

Samples were analyzed for a subset of 18 PFAS by LC/MS/MS compliant with QSM 5.3

Table B-15 at Pace Analytical Gulf Coast in Baton Rouge, Louisiana, a DoD ELAP and NELAP 

certified laboratory. The 18 PFAS analyzed as part of the ARNG SI program include the following:

• 6:2 fluorotelomer sulfonic acid (6:2 FTS)

• 8:2 fluorotelomer sulfonic acid (8:2 FTS)

• N-ethyl perfluorooctanesulfonamidoacetic 

acid (NEtFOSAA)

• N-methyl 

perfluorooctanesulfonamidoacetic acid 

(NMeFOSAA)

• Perfluorobutyrate (PFBA)

• Perfluorobutanesulfonic acid (PFBS)

• Perfluorodecanoic acid (PFDA)

• Perfluorododecanoic acid (PFDoA)

• Perfluoroheptanoic acid (PFHpA)

• Perfluorohexanoic acid (PFHxA)

• Perfluorohexanesulfonic acid (PFHxS)

• Perfluorononanoic acid (PFNA)

• Perfluorooctanoic acid (PFOA)

• Perfluorooctanesulfonic acid (PFOS)

• Perfluoropentanoic acid (PFPeA)

• Perfluorotetradecanoic acid (PFTeDA)

• Perfluorotridecanoic acid (PFTrDA)

• Perfluoroundecanoic acid (PFUdA)

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

9045D.

5.8 Deviations from SI QAPP Addendum

One deviation from the SI QAPP Addendum was identified during review of the field 

documentation. The deviation is noted below and is documented in a Field Change Request Form 

(Appendix B3):

• During the installation of temporary monitoring wells, a temporary well location at Grand 

Prairie Facility (GPF)-01 was attempted, but a 5-foot clay layer was encountered. The 

temporary well did not produce water overnight. Based on the terrain near the original well 

location, an off-set location would likely result in the same geological situation. The well

location was moved 100 feet north, east of the original location. This action was documented 

in a Field Change Request Form provided in Appendix B3. 
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AECOM 5-6

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Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, Grand Prairie AASF, Texas

Sample Identification

Sample

Collection 

Date

Sample Depth 

(feet bgs)

PFAS (LC/MS/MS QSM 5.3 Table B-15)TOC + pH (USEPA 9060A/9045D)

Comments

AOI01-01-SB-00-02 3/23/2021 0-2 x

AOI01-01-SB-00-02-MS 3/23/2021 0-2 x x MS/MSD

AOI01-01-SB-00-02-MSD 3/23/2021 0-2 x x MS/MSD

AOI01-01-SB-03-05 3/23/2021 3-5 x

AOI01-01-SB-03-05-D 3/23/2021 3-5 x Field Duplicate

AOI01-01-SB-06-08 3/23/2021 6-8 x x

AOI01-01-SB-06-08-D 3/23/2021 6-8 x x Field Duplicate

AOI01-02-SB-00-02 3/23/2021 0-2 x

AOI01-02-SB-03-05 3/23/2021 3-5 x

AOI01-02-SB-08-10 3/23/2021 8-10 x

AOI02-01-SB-00-02 3/22/2021 0-2 x

AOI02-01-SB-02-04 3/22/2021 2-4 x

AOI02-01-SB-06-08 3/22/2021 6-8 x x

AOI03-01-SB-00-02 3/22/2021 0-2 x

AOI03-01-SB-04-06 3/22/2021 4-6 x

AOI03-01-SB-08-10 3/22/2021 8-10 x x

GPF-01-SB-00-02 3/23/2021 0-2 x

GPF-01-SB-03-05 3/23/2021 3-5 x

GPF-01-SB-06-08 3/23/2021 6-8 x

GPF-02-SB-00-02 3/22/2021 0-2 x

GPF-02-SB-03-05 3/22/2021 3-5 x

GPF-02-SB-05-06 3/22/2021 5-6 x

AOI01-01-GW 3/23/2021 14 x

AOI01-01-GW-D 3/23/2021 14 x Field Duplicate

AOI01-01-GW-MS 3/23/2021 14 x MS/MSD

AOI01-01-GW-MSD 3/23/2021 14 x MS/MSD

AOI01-02-GW 3/23/2021 14.5 x

AOI02-01-GW 3/23/2021 11.35 x

AOI03-01-GW 3/22/2021 14 x

GPF-01-GW 3/24/2021 14 x

GPF-02-GW 3/22/2021 14 x

GPF-FRB-01 3/22/2021 -- x Field Blank

GPF-ERB-01 3/23/2021 -- x from DPT drill tip

GPF-ERB-02 3/23/2021 -- x from hand auger

Notes:

AOI = Area of Interest

AASF = Army Aviation Support Facility

bgs = below ground surface

D = duplicate

DPT = direct push technology

ERB = equipment rinsate blank

FRB = field reagent blank

GPF = Grand Prairie Facility

GW = groundwater

LC/MS/MS = Liquid Chromatrography Mass Spectrometry

MS/MSD = matrix spike/ matrix spike duplicate

PFAS = per- and polyfluoroalkyl substances

pH = potential for hydrogen

QSM = Quality Systems Manual

SB = soil boring

TOC =total organic carbon

USEPA = United States Environmental Protection Agency

Soil Samples

Groundwater Samples

Quality Control Samples

AECOM 5-7
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Table 5-2

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

Site Inspection Report, Grand Prairie AASF, Texas

Area of 

Interest

Boring 

Location

Soil Boring 

Depth 

(feet bgs)

Temporary Well 

Screen Interval 

(feet bgs)

Top of Casing 

Elevation 

(feet NAVD88)

Ground Surface 

Elevation 

(feet NAVD88)

Depth to 

Water

(feet btoc)

Depth to 

Water

(feet bgs)

Groundwater 

Elevation

(feet NAVD88)

AOI01-01 15 5-15 477.65 476.30 7.71 6.36 469.94

AOI01-02 15 5-15 481.67 481.40 13.35 13.08 468.32

2 AOI02-01 15 2-12 480.97 479.59 9.29 7.91 471.68

3 AOI03-01 15 10-15 482.52 481.40 12.03 10.91 470.49

GPF-01 GPF-01 15 5-15 470.52 470.30 7.92 7.70 462.60

GPF-02 GPF-02 15 5-15 477.93 477.60 3.00 2.67 474.93

Notes:

AOI = Area of Interest

AASF = Army Aviation Support Facility

bgs = below ground surface

btoc = below top of casing

GPF = Grand Prairie Facility

NAVD88 = North American Vertical Datum 1988

1

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!?

!?

!?

!?

!?

!?

Cottonwood

Bay

Diversion Channel

AOI 2

AOI 1

AOI 3

AOI01-01

AOI01-02

AOI02-01

AOI03-01

GPF-01

GPF-02

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

MB

8/10/2021

8/10/2021

NOTES Site Inspection for PFAS at Grand Prairie AASF, TX

1:3,960

8/10/2021 ­ Figure 5-1

PM CM 8/10/2021

12420 Milestone Center Drive

Germantown, MD 20876

Site Inspection Sample Locations

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

Geographics, CNES/Airbus DS, USDA, USGS,

C:\Users\stankevichm\OneDrive - AECOM Directory\ARNG_PFAS_GIS_60552172\MXDs\TX\Grand_Prairie_Figures\Grand_Prairie_SI_Figures\SI_Report\Fig_5-1_Grand_Prairie_AASF_SI_Sample_Locations.mxd

0 165 330 660

Feet

Legend

!? Soil Boring/Temporary

Monitoring Well

Area of Interest

Approximate Facility

Boundary per TX ARNG

Water Body

AECOM 5-11
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6. Site Inspection Results

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

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

through Section 6.6. Table 6-2 through Table 6-4 present PFAS results for samples with 

detections in soil or 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 (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, the AOI will proceed to the next phase 

under CERCLA. The SLs established in the OSD memorandum apply to three compounds: 

PFOS, PFOA, and PFBS. The SLs were calculated using the USEPA Office of Superfund Sites 

On-Line Calculator, which was updated on 8 April 2021 based on the release of the final Human 

Health Toxicity Values for PFBS (USEPA, 2021). 

The SLs are presented on Table 6-1 below. All other results presented in this report are 

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

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

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

Analyte

Residential

(Soil)

(μg/kg)a 

0-2 feet bgs

Industrial/ 

Commercial 

Composite 

Worker 

(Soil)

(μg/kg)a 

2-15 feet bgs

Tap Water

(Groundwater) 

(ng/L)a

PFOA 130 1,600 40

PFOS 130 1,600 40

PFBS 1,900 25,000 600

Notes:

a.) 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. 

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

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

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

receptors identified at the site: the residential scenario is applied to surface soil results (0 to 2 feet 

bgs) and the industrial/commercial worker scenario is applied to shallow subsurface soil results 

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

15 feet is the anticipated limit of construction activities. 

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. 
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 6-2

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

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

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

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

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

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

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

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

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

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

solid phases (ITRC, 2018).

6.3 AOI 1 

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

1, which includes three potential PFAS release areas: Wash Rack, Hazardous Storage Building, 

and Fuel Station. The detected compounds in soil and groundwater are summarized on Table 6-

2 through Table 6-4. The detections of PFOA, PFOS, and PFBS in soil and groundwater are 

presented on Figure 6-1 through Figure 6-4. 

6.3.1 AOI 1 Soil Analytical Results

PFOA, PFOS, and PFBS did not exceed the SLs in soil at the three potential PFAS release areas:

Wash Rack, Hazardous Storage Building, and Fuel Station. Figure 6-1 through Figure 6-3

present the ranges of detections of PFOA, PFOS, and PFBS in soil. Table 6-2 and Table 6-3

summarize the detected compounds in soil. 

At the location where wastewater from the Wash Rack and OWS would have discharged to the 

surface, soil was sampled from surface soil (0 to 2 feet bgs), intermediate subsurface soil (3 to 5 

feet bgs), and deep subsurface soil (6 to 8 feet bgs) from boring location AOI01-01. PFOA and 

PFOS were detected in soil at concentrations several orders of magnitude lower than the SLs. 

PFOA was detected at all three depths with concentrations ranging from 0.110 J micrograms per 

kilogram (μg/kg) to 0.358 J μg/kg. PFOS was only detected in the surface soil sample (0 to 2 feet 

bgs) at a concentration of 0.367 J μg/kg. PFBS was not detected at AOI01-01.

At the Fuel Station, soil was sampled from surface soil (0 to 2 feet bgs), intermediate subsurface 

soil (3 to 5 feet bgs), and deep subsurface soil (8 to 10 feet bgs) from boring location AOI01-02. 

PFOA was detected in soil at concentrations several orders of magnitude lower than the SLs. 

PFOA was detected in subsurface soil (3 to 5 feet bgs and 8 to 10 feet bgs) at concentrations of 

0.161 J μg/kg and 0.107 J μg/kg, respectively. PFOA was not detected in surface soil (0 to 2 feet 

bgs) at AOI01-02. PFOS and PFBS were not detected at AOI01-02. 

6.3.2 AOI 1 Groundwater Analytical Results

PFOA exceeded the SLs in groundwater at the potential PFAS release areas at AOI 1. Figure 6-

4 presents the ranges of detections of PFOA, PFOS, and PFBS in groundwater. Table 6-4 

summarizes the detected compounds in groundwater. 

At the location where wastewater from the Wash Rack and OWS or where any releases from the 

Hazardous Material Storage Building would have discharged to the surface, groundwater was 

sampled from temporary monitoring well location AOI01-01. The SL of 40 ng/L for PFOA was 

exceeded at AOI01-01 at a concentration of 106 J+ ng/L. PFOS was detected below the SL of 40 

ng/L at a concentration of 23.5 ng/L. PFBS was detected below the SL of 600 ng/L at a 

concentration of 3.24 J ng/L. 
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 6-3

At the Fuel Station, groundwater was sampled from temporary monitoring well location AOI01-02. 

The SL of 40 ng/L for PFOA was exceeded at AOI01-02 at a concentration of 94.4 ng/L. PFOS 

was detected below the SL of 40 ng/L at a concentration of 6.37 ng/L. PFBS was detected below 

the SL of 600 ng/L at a concentration of 1.75 J ng/L. 

6.3.3 AOI 1 Conclusions

Based on the results of the SI, PFOA, PFOS, and PFBS were detected in soil at AOI 1; however, 

the detected concentrations were several orders of magnitude lower than the soil SLs. At locations 

AOI01-01 and AOI01-02, PFOA was detected in groundwater at concentrations exceeding the SL 

of 40 ng/L. PFOS and PFBS were detected in groundwater at concentrations below their 

respective SLs. Based on the exceedances of the SL for PFOA in groundwater, further evaluation 

at AOI 1 is warranted. 

6.4 AOI 2 

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

2, which includes one potential PFAS release area: Flight Line Ramp. The detected compounds 

in soil and groundwater are summarized on Table 6-2 through Table 6-4. The detections of PFOA, 

PFOS, and PFBS in soil and groundwater are presented on Figure 6-1 through Figure 6-4. 

6.4.1 AOI 2 Soil Analytical Results

PFOA, PFOS, and PFBS did not exceed the SLs in soil at the potential PFAS release area: Flight 

Line Ramp. Figure 6-1 through Figure 6-3 present the ranges of detections of PFOA, PFOS, and 

PFBS in soil. Table 6-2 and Table 6-3 summarize the detected compounds in soil. 

At the Flight Line Ramp, soil was sampled from surface soil (0 to 2 feet bgs), intermediate 

subsurface soil (2 to 4 feet bgs), and deep subsurface soil (6 to 8 feet bgs) from boring location 

AOI02-01. PFOA, PFOS, and PFBS were detected in soil at concentrations several orders of 

magnitude lower than the SLs. PFOA and PFOS were detected in surface soil (0 to 2 feet bgs) at 

concentrations of 0.069 J μg/kg and 0.472 J μg/kg, respectively. PFBS was not detected in surface 

soil. PFOA, PFOS, and PFBS were not detected in subsurface soil. 

6.4.2 AOI 2 Groundwater Analytical Results

PFOA, PFOS, and PFBS did not exceed the SLs in groundwater at the potential PFAS release 

area: Flight Line Ramp. Figure 6-4 presents the ranges of detections of PFOA, PFOS, and PFBS 

in groundwater. Table 6-4 summarizes the detected compounds in groundwater. 

At the Flight Line Ramp, groundwater was sampled from temporary monitoring well location 

AOI02-01. PFOA was detected below the SL of 40 ng/L at a concentration of 33.3 ng/L. PFOS 

was detected below the SL of 40 ng/L at a concentration of 39.0 ng/L. PFBS was detected below 

the SL of 600 ng/L at a concentration of 37.5 ng/L. 

6.4.3 AOI 2 Conclusions

Based on the results of the SI, PFOA, PFOS, and PFBS were detected in surface soil at AOI 2; 

however, the detected concentrations were several orders of magnitude lower than the soil SLs. 

PFOA, PFOS, and PFBS were detected in groundwater at concentrations below their respective

SLs. Therefore, further evaluation at AOI 2 is not warranted. 
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 6-4

6.5 AOI 3

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

3, which includes one potential PFAS release area: Former Firetruck Location. The detected 

compounds in soil and groundwater are summarized on Table 6-2 through Table 6-4. The 

detections of PFOA, PFOS, and PFBS in soil and groundwater are presented on Figure 6-1

through Figure 6-4.

6.5.1 AOI 3 Soil Analytical Results

PFOA, PFOS, and PFBS did not exceed the SLs in soil at the potential PFAS release area: Former 

Firetruck Location. Figure 6-1 through Figure 6-3 present the ranges of detections of PFOA, 

PFOS, and PFBS in soil. Table 6-2 and Table 6-3 summarize the detected compounds in soil.

At the Former Firetruck Location, soil was sampled from surface soil (0 to 2 feet bgs), intermediate 

subsurface soil (4 to 6 feet bgs), and deep subsurface soil (8 to 10 feet bgs) from boring location 

AOI03-01. PFOA, PFOS, and PFBS were detected in soil at concentrations several orders of 

magnitude lower than the SLs. PFOA, PFOS and PFBS were detected in surface soil (0 to 2 feet 

bgs) at concentrations of 0.518 J μg/kg, 0.523 J μg/kg and 0.061 J μg/kg, respectively. PFOA, 

PFOS, and PFBS were not detected in subsurface soil.

6.5.2 AOI 3 Groundwater Analytical Results

PFOA, PFOS, and PFBS did not exceed the SLs in groundwater at the potential PFAS release 

area: Former Firetruck Location. Figure 6-4 presents the ranges of detections of PFOA, PFOS, 

and PFBS in groundwater. Table 6-4 summarizes the detected compounds in groundwater. 

At the Former Firetruck Location, groundwater was sampled from temporary monitoring well 

location AOI03-01. PFOA was detected below the SL of 40 ng/L at a concentration of 9.71 ng/L. 

PFOS was detected below the SL of 40 ng/L at a concentration of 2.97 ng/L. PFBS was detected 

below the SL of 600 ng/L at a concentration of 14.8 ng/L.

6.5.3 AOI 3 Conclusions

Based on the results of the SI, PFOA, PFOS, and PFBS were detected in surface soil at AOI 3; 

however, the detected concentrations were several orders of magnitude lower than the soil SLs. 

PFOA, PFOS, and PFBS were detected in groundwater at concentrations below their respective 

SLs. Therefore, further evaluation at AOI 3 is not warranted. 

6.6 Facility Boundary

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

facility boundary, which includes one downgradient location near the northern boundary (GPF-01)

to determine if potential PFAS impacts are migrating offsite, and one upgradient location on the

eastern side (GPF-02) to determine if potential PFAS impacts are migrating from offsite to onsite. 

The detected compounds in soil and groundwater are summarized on Table 6-2 through Table 6-

4. The detections of PFOA, PFOS, and PFBS in soil and groundwater are presented on Figure 

6-1 through Figure 6-4.

6.6.1 Facility Boundary Soil Analytical Results

PFOA, PFOS, and PFBS did not exceed the SLs in soil at the potential facility boundary. Figure 

6-1 through Figure 6-3 present the ranges of detections of PFOA, PFOS, and PFBS in soil. Table 

6-2 and Table 6-3 summarize the detected compounds in soil.
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 6-5

At the downgradient location GPF-01, soil was sampled from surface soil (0 to 2 feet bgs), 

intermediate subsurface soil (3 to 5 feet bgs), and deep subsurface soil (6 to 8 feet bgs) from the 

boring location. PFOA, PFOS, and PFBS were detected in soil at concentrations several orders 

of magnitude lower than the SLs. PFOA was detected at all three depths with concentrations 

ranging from 0.075 J μg/kg to 3.5 μg/kg. PFOS was detected in subsurface soil (3 to 5 feet bgs 

and 6 to 8 feet bgs) at concentrations of 1.42 μg/kg and 1.03 J μg/kg, respectively. PFBS was 

detected subsurface soil (3 to 5 feet bgs and 6 to 8 feet bgs) at concentrations of 0.171 J μg/kg 

and 0.066 J μg/kg, respectively. PFOS and PFBS were not detected in surface soil (0 to 2 feet 

bgs) at GPF-01.

At the upgradient location GPF-02, soil was sampled from surface soil (0 to 2 feet bgs), 

intermediate subsurface soil (3 to 5 feet bgs), and deep subsurface soil (5 to 6 feet bgs) from the 

boring location. PFOA, PFOS, and PFBS were not detected in soil at GPF-02. 

6.6.2 Facility Boundary Groundwater Analytical Results

PFOA exceeded the SLs for PFOA of 40 ng/L in groundwater at the facility boundary location 

(GPF-01). Figure 6-4 presents the ranges of detections of PFOA, PFOS, and PFBS in 

groundwater. Table 6-4 summarizes the detected compounds in groundwater. 

At the downgradient location GPF-01, groundwater was sampled from the temporary monitoring 

well location. The SL of 40 ng/L for PFOA was exceeded at a concentration of 369 ng/L. PFOS 

was detected below the SL of 40 ng/L at a concentration of 13.0 ng/L. PFBS was detected below 

the SL of 600 ng/L at a concentration of 32.9 ng/L. 

At the upgradient location GPF-02, groundwater was sampled from the temporary monitoring well 

location. PFOA was detected below the SL of 40 ng/L at a concentration of 15.1 ng/L. PFOS was 

detected below the SL of 40 ng/L at a concentration of 8.08 ng/L. PFBS was detected below the 

SL of 600 ng/L at a concentration of 2.79 J ng/L.

6.6.3 Facility Boundary Conclusions

Based on the results of the SI, PFOA, PFOS, and PFBS were detected in soil at the facility 

boundary; however, the detected concentrations were several orders of magnitude lower than the 

soil SLs. At location GPF-01, PFOA was detected in groundwater at a concentration exceeding 

the SL of 40 ng/L. PFOS and PFBS were detected in groundwater at concentrations below their 

respective SLs. Based on the exceedances of the SL for PFOA in groundwater, further evaluation 

at the facility boundary is warranted. 
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 6-6

THIS PAGE INTENTIONALLY BLANK
Table 6-2

PFAS Detections in Surface Soil

Site Inspection Report, Grand Prairie AASF

Analyte OSD Screening 

Level a,b

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

Soil, PFAS by LCMSMS Compliant with QSM 5.3 Table B-15 (μg/kg)PFBS 1900 ND ND ND 0.061 J ND NDPFDA - ND ND 0.067 J ND ND NDPFHxA - 0.106 J ND ND 0.163 J ND NDPFHxS - ND ND 0.241 J ND ND NDPFOA 130 0.358 J ND 0.069 J 0.518 J 0.075 J NDPFOS 130 0.367 J ND 0.472 J 0.523 J ND NDPFPeA - 0.134 J ND ND 0.082 J ND ND

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abb

PFAS PFBS PFDA PFHxA 

References PFHxS 

PFOA PFOS PFPeA 

Interpreted Qualifiers Acronyms and 

J = Estimated concentration AASF 

AOI ft GPF HQ ID LCMSMS LOD ND OSD QSM Qual SB USEPA μg/kg - 

AOI1 AOI2

AOI02-01-SB-00-02

03/22/2021

0 - 2 ft

GPF-02

GPF-02-SB-00-02

03/22/2021

0 - 2 ft

GPF-01

GPF-01-SB-00-02

03/23/2021

0 - 2 ft

a. Assistant Secretary of Defense, 2019. Risk Based Screening Levels Calculated for PFOS and PFOA in Groundwater or Soil using USEPA’s Regional Screening Level Calculator. HQ=0.1. 15 October 2019. Soilscreening levels based on residential scenario for incidental ingestion of contaminated soil.b. USEPA, 2021. Risk Based Screening Levels Calculated for PFBS in Groundwater and Soil using USEPA's Regional Screening Level Calculator. HQ=0.1. 8 April 2021.

AOI3

AOI03-01-SB-00-02

03/22/2021

0 - 2 ft 0 - 2 ft

Area of Interest

Sample ID

Sample Date

Depth

AOI01-01-SB-00-02

03/23/2021

0 - 2 ft

AOI01-02-SB-00-02

03/23/2021

AECOM 
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

THIS PAGE INTENTIONALLY BLANK

AECOM 6-8
Table 6-3

PFAS Detections in Subsurface Soil

Site Inspection Report, Grand Prairie AASF

Analyte OSD Screening 

Level a,b

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

Soil, PFAS by LCMSMS Compliant with QSM 5.3 Table B-15 (μg/kg)

6:2 FTS - ND ND ND ND ND ND ND ND 0.093 J ND

PFBS 25000 ND ND ND ND ND ND ND ND ND ND

PFHpA - ND ND ND ND ND ND ND ND ND ND

PFHxA - ND ND ND ND ND ND ND ND ND ND

PFHxS - ND ND ND ND ND ND ND ND ND ND

PFOA 1600 0.262 J 0.151 J 0.248 J 0.110 J 0.161 J 0.107 J ND ND ND ND

PFOS 1600 ND ND ND ND ND ND ND ND ND ND

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

6:2 FTS 6:2 fluorotelomer sulfonate

PFAS per- and polyfluoroalkyl substances

PFBS perfluorobutanesulfonic acid

PFHpA perfluoroheptanoic acid

References PFHxA perfluorohexanoic acid

PFHxS perfluorohexanesulfonic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AASF Army Aviation Support Facility

AOI Area of Interest

D Duplicate

ft feet

GPF Grand Prairie Facility

HQ Hazard quotient

ID Identification

LCMSMS Liquid Chromatography Mass Spectrometry

LOD Limit of Detection

ND Analyte not detected above the LOD

OSD Office of the Secretary of Defense

QSM Quality Systems Manual

Qual Interpreted Qualifier

SB Soil boring

USEPA United States Environmental Protection Agency

μg/kg micrograms per kilogram

- Not applicable

a. Assistant Secretary of Defense, 2019. Risk Based Screening Levels Calculated for PFOS and PFOA in Groundwater or Soil using USEPA’s Regional Screening Level Calculator. HQ=0.1. 15 October 2019.

Soil screening levels based on industrial/commercial composite worker scenario for incidental ingestion of contaminated soil.

b. USEPA, 2021. Risk Based Screening Levels Calculated for PFBS in Groundwater and Soil using USEPA's Regional Screening Level Calculator. HQ=0.1. 8 April 2021.

Area of Interest

Sample ID

Sample Date

Depth

AOI01-01-SB-03-05

03/23/2021

3 - 5 ft 3 - 5 ft

AOI01-01-SB-06-08

03/23/2021

6 - 8 ft

AOI01-01-SB-06-08-D

03/23/2021

6 - 8 ft

AOI03-01-SB-08-10

03/22/2021

8 - 10 ft

AOI1 AOI2 AOI3

AOI01-01-SB-03-05-D

03/23/2021

AOI03-01-SB-04-06

03/22/2021

4 - 6 ft

AOI02-01-SB-02-04

03/22/2021

2 - 4 ft

AOI02-01-SB-06-08

03/22/2021

3 - 5 ft 6 - 8 ft

AOI01-02-SB-08-10

03/23/2021

8 - 10 ft

AOI01-02-SB-03-05

03/23/2021

AECOM 6-9
Table 6-3

PFAS Detections in Shallow Subsurface Soil

Site Inspection Report, Grand Prairie AASF

Analyte OSD Screening 

Level a,b

Result Qual Result Qual Result Qual Result Qual

Soil, PFAS by LCMSMS Compliant with QSM 5.3 Table B-15 (μg/kg)

6:2 FTS - ND ND ND ND

PFBS 25000 0.171 J 0.066 J ND ND

PFHpA - 0.099 J ND ND ND

PFHxA - 0.678 J 0.069 J ND ND

PFHxS - 7.48 0.621 J ND ND

PFOA 1600 3.50 0.596 J ND ND

PFOS 1600 1.42 1.03 J ND ND

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

6:2 FTS 6:2 fluorotelomer sulfonate

PFAS per- and polyfluoroalkyl substances

PFBS perfluorobutanesulfonic acid

PFHpA perfluoroheptanoic acid

References PFHxA perfluorohexanoic acid

PFHxS perfluorohexanesulfonic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AASF Army Aviation Support Facility

AOI Area of Interest

D Duplicate

ft feet

GPF Grand Prairie Facility

HQ Hazard quotient

ID Identification

LCMSMS Liquid Chromatography Mass Spectrometry

LOD Limit of Detection

ND Analyte not detected above the LOD

OSD Office of the Secretary of Defense

QSM Quality Systems Manual

Qual Interpreted Qualifier

SB Soil boring

USEPA United States Environmental Protection Agency

μg/kg micrograms per kilogram

- Not applicable

03/22/2021 03/22/2021

3 - 5 ft 5 - 6 ft

b. USEPA, 2021. Risk Based Screening Levels Calculated for PFBS in Groundwater and Soil using USEPA's Regional Screening Level Calculator. HQ=0.1. 8 April 2021.

a. Assistant Secretary of Defense, 2019. Risk Based Screening Levels Calculated for PFOS and PFOA in Groundwater or Soil using USEPA’s Regional Screening Level Calculator. HQ=0.1. 15 October 2019.

Soil screening levels based on industrial/commercial composite worker scenario for incidental ingestion of contaminated soil.

Area of Interest

Sample ID

Sample Date

Depth

GPF-01-SB-06-08

03/23/2021

6 - 8 ft

GPF-01

GPF-01-SB-03-05

03/23/2021

3 - 5 ft

GPF-02-SB-03-05

GPF-02

GPF-02-SB-05-06

AECOM 6-10
Table 6-4

PFAS Detections in Groundwater

Site Inspection Report, Grand Prairie AASF

Analyte OSD Screening 

Level a,b

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

PFBA - 10.3 9.38 10.6 23.7 12.4 56.5 11.7

PFBS 600 3.24 J 2.97 J 1.75 J 37.5 14.8 32.9 2.79 

PFHpA - 7.25 7.12 8.03 13.3 2.92 J 11.1 7.07PFHxA - 13.3 12.2 11.0 66.1 17.6 100 12.9

PFHxS - 23.9 24.6 25.9 88.6 68.6 946 8.92

PFNA - LOD UJ 1.39 J 1.99 J LOD LOD LOD LOD

PFOA 40 106 J+ 106 J+ 94.4 33.3 9.71 369 15.1

PFOS 40 19.6 23.5 6.37 39.0 2.97 J 13.0 8.08

PFPeA - 9.82 9.35 10.8 29.2 6.54 18.2 15.7

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical AbbreviationsBold Font Detected concentration exceeded USEPA HA Screening Levels PFAS 

PFBA PFBS PFHpA 

References PFHxA 

PFHxS PFNA PFOA PFOS 

Interpreted Qualifiers PFPeA J = Estimated concentrationJ+ = Estimated concentration, biased high Acronyms and Abbreviations

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

AOI D DL GPF GW HA HQ ID LCMSMS LOD ND OSD QSM Qual USEPA ng/L - 

AOI01-01-GW-D

03/23/2021

AOI01-02-GW

03/23/2021

Area of Interest

Sample ID

Sample Date

AOI01-01-GW

03/23/2021

b. USEPA, 2021. Risk Based Screening Levels Calculated for PFBS in Groundwater and Soil using USEPA's Regional Screening Level Calculator. HQ=0.1. 8 April 2021.

Water, PFAS by LCMSMS Compliant with QSM 5.3 Table B-15 (ng/L)

AOI1 GPF-01

GPF-01-GW

03/24/2021

GPF

GPF-0

03/22/

AOI2

AOI02-01-GW

03/23/2021

AOI3

AOI03-01-GW

a. Assistant Secretary of Defense, 2019. Risk Based Screening Levels Calculated for PFOS and PFOA in Groundwater or Soil using USEPA’s Regional Screening Level Calculator. HQ=0.1. 15October 2019. Groundwater screening levels based on residential scenario for direct ingestion of groundwater.

03/22/2021

AECOM 
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

THIS PAGE INTENTIONALLY BLANK

AECOM 6-12
Cottonwood

Bay

Diversion Channel

AOI01-01

AOI01-02

AOI02-01

AOI03-01

GPF-01

GPF-02

Cottonwood

Bay

Diversion Channel

AOI01-01

AOI01-02

AOI02-01

AOI03-01

GPF-01

GPF-02

­ Figure 6-1

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection for PFAS at Grand Prairie AASF, TX

11/2/2021

11/2/2021

11/2/2021

MS

MB

CM

GIS BY

CHK BY

PM

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

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

11/2/2021

1:5,263

C:\Users\stankevichm\OneDrive - AECOM Directory\ARNG_PFAS_GIS_60552172\MXDs\TX\Grand_Prairie_Figures\Grand_Prairie_SI_Figures\SI_Report\Fig_6-1_Grand_Prairie_AASF_SI_Soil_PFOS_Results.mxd

PFOS Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

0 220 440 880

Feet

PFOS Results (μg/Kg)

ND

>ND - 10

>10 - 130

>130 - 1,600

>1,600

Approximate Facility

Boundary per TX ARNG

Water Body

Surface Water Flow

Direction

Groundwater Flow Direction

Cottonwood

Bay

Diversion Channel

AOI01-01

AOI01-02

AOI02-01

AOI03-01

GPF-01

GPF-02

Shallow Intermediate Deep

AECOM 6-13
Cottonwood

Bay

Diversion Channel

AOI01-01

AOI01-02

AOI02-01

AOI03-01

GPF-01

GPF-02

Cottonwood

Bay

Diversion Channel

AOI01-01

AOI01-02

AOI02-01

AOI03-01

GPF-01

GPF-02

­ Figure 6-2

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection for PFAS at Grand Prairie AASF, TX

11/2/2021

11/2/2021

11/2/2021

MS

MB

CM

GIS BY

CHK BY

PM

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

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

11/2/2021

1:5,263

C:\Users\stankevichm\OneDrive - AECOM Directory\ARNG_PFAS_GIS_60552172\MXDs\TX\Grand_Prairie_Figures\Grand_Prairie_SI_Figures\SI_Report\Fig_6-2_Grand_Prairie_AASF_SI_Soil_PFOA_Results.mxd

PFOA Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

0 220 440 880

Feet

PFOA Results (μg/Kg)

ND

>ND - 10

>10 - 130

>130 - 1,600

>1,600

Approximate Facility

Boundary per TX ARNG

Water Body

Surface Water Flow

Direction

Groundwater Flow Direction

Cottonwood

Bay

Diversion Channel

AOI01-01

AOI01-02

AOI02-01

AOI03-01

GPF-01

GPF-02

Shallow Intermediate Deep

AECOM 6-14
Cottonwood

Bay

Diversion Channel

AOI01-01

AOI01-02

AOI02-01

AOI03-01

GPF-01

GPF-02

Cottonwood

Bay

Diversion Channel

AOI01-01

AOI01-02

AOI02-01

AOI03-01

GPF-01

GPF-02

­ Figure 6-3

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection for PFAS at Grand Prairie AASF, TX

11/2/2021

11/2/2021

11/2/2021

MS

JZ

CM

GIS BY

CHK BY

PM

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

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

11/2/2021

1:5,263

C:\Users\stankevichm\OneDrive - AECOM Directory\ARNG_PFAS_GIS_60552172\MXDs\TX\Grand_Prairie_Figures\Grand_Prairie_SI_Figures\SI_Report\Fig_6-3_Grand_Prairie_AASF_SI_Soil_PFBS_Results.mxd

PFBS Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

0 220 440 880

Feet

PFBS Results (μg/Kg)

ND

>ND - 10

>10 - 1,900

>1,900 - 25,000

>25,000

Approximate Facility

Boundary per TX ARNG

Water Body

Surface Water Flow

Direction

Groundwater Flow Direction

Cottonwood

Bay

Diversion Channel

AOI01-01

AOI01-02

AOI02-01

AOI03-01

GPF-01

GPF-02

Shallow Intermediate Deep

AECOM 6-15
Cottonwood

Bay

AOI01-01

AOI01-02

AOI02-01

AOI03-01

GPF-01

GPF-02

Cottonwood

Bay

AOI01-01

AOI01-02

AOI02-01

AOI03-01

GPF-01

GPF-02

­ Figure 6-4

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection for PFAS at Grand Prairie AASF, TX

11/2/2021

11/2/2021

11/2/2021

MS

MB

CM

GIS BY

CHK BY

PM

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

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

11/2/2021

1:5,280

C:\Users\stankevichm\OneDrive - AECOM Directory\ARNG_PFAS_GIS_60552172\MXDs\TX\Grand_Prairie_Figures\Grand_Prairie_SI_Figures\SI_Report\Fig_6-4_Grand_Prairie_AASF_SI_GW_PFOA_PFOS_PFBS.mxd

PFOS, PFOA, PFBS Detections in Groundwater

12420 Milestone Center Drive

Germantown, MD 20876

PFOA Results (ng/L)

ND

>ND - 10

>10 - 40

>40 - 70

>70 - 400

>400

0 220 440 880

Feet

PFOS Results (ng/L)

ND

>ND - 10

>10 - 40

>40 - 70

>70 - 400

>400

Approximate Facility

Boundary per TX ARNG

Water Body

Surface Water Flow

Direction

Groundwater Flow Direction

PFOS PFOA

Cottonwood

Bay

AOI01-01

AOI01-02

AOI02-01

AOI03-01

GPF-01

GPF-02

PFBS

PFBS Results (ng/L)

ND

>ND - 100

>100 - 600

>600 - 1,000

>1,000 - 6,000

>6,000

AECOM 6-16
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 7-1

7. Exposure Pathways

The CSMs for each AOI, revised based on the SI findings, are presented on Figure 7-1 through 

Figure 7-7. A CSM presents the current understanding of the site conditions with respect to known 

and suspected sources, potential transport mechanisms and migration pathways, and potentially 

exposed human receptors. A human exposure pathway is considered potentially complete when 

the following conditions are present:

1. Contaminant source;

2. Environmental fate and transport;

3. Exposure point;

4. Exposure route; and

5. Potentially exposed populations.

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

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

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

PFOA, PFOS, or PFBS are detected, in which case the CSM figure uses a half-filled circle symbol 

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

is used to indicate when a potentially complete exposure pathway has detections of PFOA, PFOS, 

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

investigation. 

In general, the potential routes of exposure to PFAS 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, 

trespassers, residents outside the facility boundary, and recreational users outside of the facility 

boundary. This SI programmatically focuses on potential human exposures and does not address 

potential ecological receptors.

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 the AOIs based on the 

aforementioned criteria. 

7.1.1 AOI 1

Between 2000 and 2012, AFFF was used during fire training activities at the Wash Rack and 

AFFF was stored at the hazardous materials storage building and the fuel station. PFOA and 

PFOS were detected in soil at AOI 1 and confirm the release of PFAS to soil. 

Based on the results of the SI in AOI 1, ground-disturbing activities could potentially result in site 

worker, future construction worker, trespasser, recreational user, and future resident exposure to 

PFOA and PFOS via inhalation of dust and ingestion of surface soil. Ground-disturbing activities 

could also potentially result in construction worker exposure to PFOA in subsurface soil via 

ingestion. The CSM is presented on Figure 7-1. 
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 7-2

7.1.2 AOI 2

From 2000 to 2012, AFFF was used during fire training activities at the Flight Line Ramp. PFOA

and PFOS were detected in soil at AOI 2 and confirm the release of PFAS to soil in AOI 2. Based 

on the results of the SI in AOI 2, ground-disturbing activities could potentially result in site worker, 

future construction worker, trespasser, recreational user, and future resident exposure to PFOA 

and PFOS via inhalation of dust and ingestion of surface soil. The CSM is presented on Figure 

7-2.

7.1.3 AOI 3

A firetruck equipped with AFFF was historically stored in the southern corner of the facility. PFOA, 

PFOS, and PFBS were detected in surface soil at AOI 3 and confirm the release of PFAS to soil 

in AOI 3. Based on the results of the SI in AOI 3, ground-disturbing activities could potentially 

result in site worker, future construction worker, trespasser, recreational user, and future resident 

exposure to PFOA, PFOS, and PFBS via inhalation of dust and ingestion of surface soil. The 

CSM is presented on Figure 7-3.

7.1.4 Facility Boundary

PFOA, PFOS, and PFBS were detected in soil near the facility boundary. Based on the results of 

the SI near the facility boundary, ground-disturbing activities could potentially result in site worker, 

future construction worker, trespasser, recreational user, and future resident exposure to PFOA 

via inhalation of dust and ingestion of surface soil. Ground-disturbing activities could also 

potentially result in construction worker exposure to PFOA, PFOS, and PFBS in subsurface soil 

via ingestion. The CSM is presented on Figure 7-4.

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 the AOIs based 

on the aforementioned criteria. Grand Prairie AASF receives its potable water from the City of 

Grand Prairie; therefore, the ingestion exposure pathway for site workers and trespassers is 

considered incomplete. A query of the Texas Water Development Board Submitted Drillers 

Reports Database identified the presence of public supply wells and domestic wells downgradient 

from Grand Prairie AASF. However, these wells range in depth from 80 ft bgs to 1158 ft bgs. Of 

these wells, the shallowest well is an 80-foot-deep domestic well 4 miles away and the closest 

well is a 2,084-foot-deep public supply well located within a mile of the facility. Groundwater within 

the facility boundary is shallow ranging from 2.67 feet bgs to 13.08 feet bgs during the SI. 

Therefore, based on the depth of the downgradient wells and distance from the facility, the 

ingestion exposure pathway for residential receptors is considered incomplete. 

7.2.1 AOI 1

PFOA exceeded the SL in two temporary monitoring wells in AOI 1. PFOS and PFBS were 

detected in groundwater from the two temporary monitoring wells at concentrations below SLs. 

Depths to water measured in March 2021 during the SI ranged from 6.36 to 13.08 feet bgs. 

Therefore, groundwater may be encountered during construction activities and the ingestion 

exposure pathway for construction workers is considered potentially complete. The CSM is 

presented on Figure 7-1. 
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 7-3

7.2.2 AOI 2 

PFOA, PFOS, and PFBS were detected in groundwater from one temporary monitoring well at 

AOI 2 at concentrations below SLs. Depth to water measured at this well in March 2021 during 

the SI was 7.91 feet bgs. Therefore, groundwater may be encountered during construction 

activities and the ingestion exposure pathway for construction workers is considered potentially 

complete. The CSM is presented on Figure 7-2. 

7.2.3 AOI 3 

PFOA, PFOS, and PFBS were detected in groundwater from one temporary monitoring well at 

AOI 3 at concentrations below SLs. Depth to water measured at this well in March 2021 during 

the SI was 10.91 feet bgs. Therefore, groundwater may be encountered during construction 

activities and the ingestion exposure pathway for construction workers is considered potentially 

complete. The CSM is presented on Figure 7-3. 

7.2.4 Facility Boundary

PFOA exceeded the SL in one temporary monitoring well near the northern facility boundary. 

PFOA was detected in groundwater from one temporary monitoring well near the eastern 

boundary at a concentration below the SL. PFOS and PFBS were detected in groundwater from 

the two temporary monitoring wells at concentrations below SLs. Depths to water measured in 

March 2021 during the SI ranged from 2.67 to 7.70 feet bgs. Therefore, groundwater may be 

encountered during construction activities and the ingestion exposure pathway for construction 

workers is considered potentially complete. The CSM is presented on Figure 7-4. 

7.3 Surface Water and Sediment Exposure Pathway

No surface water or sediment features exist within the facility; therefore, the exposure pathways 

via surface water or sediment for incidental ingestion are considered incomplete. However, the 

facility is bordered to the north and west by Cottonwood Bay. Surface water and groundwater flow 

direction is towards Cottonwood Bay and may present a potentially complete pathway for 

contamination to surface water and sediment within the bay for the recreational user. 
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 7-4

THIS PAGE INTENTIONALLY BLANK
Media

SOURCE PATHWAY RECEPTOR

AOI 1 

AFFF release 

during AFFF fire 

extinguisher testing/

training at the wash 

rack, and storage of 

AFFF in the Haz. 

Materials Storage 

Building and the 

Fuel Station 

PFAS in 

Surface Soil 

near AOI 1 

PFAS in 

Subsurface 

Soil via soil 

infiltration 

and from 

leaks in 

drains, 

OWS, and 

underground 

piping

Human 

Activities

Precipitation/ 

Run-Off

Leaching/ 

Infiltration

Airborne Soil 

particulate

Surface Soil 

at AOI

Surface 

Water/ 

sediment3 Subsurface 

Soil

Shallow 

Groundwater

Source Release 

Mechanism Media Transport and Migration Media Exposure Routes

Inhalation of 

Dust

Ingestion

Ingestion

Ingestion

Ingestion

Human Receptors: 

Current/ Future

Flow-Chart Continues

Partial / Possible Flow

Flow-Chart Stops

Incomplete Pathway

Potentially Complete Pathway

Complete Pathway

Site Worker Construction Worker2 Resident1 Trespasser/ Recreational User

Site Worker Construction Worker2 Resident1 Trespasser/ Recreational User

/ /

LEGEND

/ /

/ / /

Figure 7-1

Preliminary Conceptual Site Model, AOI 1

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

/

/

/

/

/

/ /

/

/

Note: 

1. The residential receptor

refers to future residential

properties planned by the City

of Dallas.

2. No current active

construction at the facility.

/

/ / /

7-5
Media

SOURCE PATHWAY RECEPTOR

AOI 2 

AFFF release

during AFFF fire 

extinguisher testing/

training at the flight 

line ramp 

PFAS in 

Surface Soil 

near AOI 2 

PFAS in 

Subsurface 

Soil via soil 

infiltration 

Human 

Activities

Precipitation/ 

Run-Off

Leaching/ 

Infiltration

Airborne Soil 

particulate

Surface Soil 

at AOI

Surface 

Water/ 

sediment3 Subsurface 

Soil

Shallow 

Groundwater

Source Release 

Mechanism Media Transport and Migration Media Exposure Routes

Inhalation of 

Dust

Ingestion

Ingestion

Ingestion

Ingestion

Human Receptors: 

Current/ Future

Flow-Chart Continues

Partial / Possible Flow

Flow-Chart Stops

Incomplete Pathway

Potentially Complete Pathway

Complete Pathway

Site Worker Construction Worker2 Resident1 Trespasser/ Recreational User

Site Worker Construction Worker2 Resident1 Trespasser/ Recreational User

/

LEGEND

/ /

/ / /

Figure 7-2

Preliminary Conceptual Site Model, AOI 2

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

/

/

/

/

/

/ /

/

/

Note: 

1. The residential receptor

refers to future residential

properties planned by the City

of Dallas.

2. No current active

construction at the facility.

/

/ / /

/

7-6
Media

SOURCE PATHWAY RECEPTOR

AOI 3 Storage of AFFF in 

the Firetruck

PFAS in 

Surface Soil 

near AOI 3 

PFAS in 

Subsurface 

Soil via soil 

infiltration 

Human 

Activities

Precipitation/ 

Run-Off

Leaching/ 

Infiltration

Airborne Soil 

particulate

Surface Soil 

at AOI

Surface 

Water/ 

sediment3 Subsurface 

Soil

Shallow 

Groundwater

Source Release 

Mechanism Media Transport and Migration Media Exposure Routes

Inhalation of 

Dust

Ingestion

Ingestion

Ingestion

Ingestion

Human Receptors: 

Current/ Future

Flow-Chart Continues

Partial / Possible Flow

Flow-Chart Stops

Incomplete Pathway

Potentially Complete Pathway

Complete Pathway

Site Worker Construction Worker2 Resident1 Trespasser/ Recreational User

Site Worker Construction Worker2 Resident1 Trespasser/ Recreational User

/

LEGEND

/ /

/ / /

Figure 7-3

Preliminary Conceptual Site Model, AOI 3

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

/

/

/

/

/

/ /

/

/

Note: 

1. The residential receptor

refers to future residential

properties planned by the City

of Dallas.

2. No current active

construction at the facility.

/

/ / /

/

7-7
Media

SOURCE PATHWAY RECEPTOR

Facility 

Boundary 

AFFF release 

during AFFF fire 

extinguisher testing/

training at the wash

rack and the flight 

line ramp, and 

storage of AFFF in 

the Haz. Materials 

Storage Building 

and the Fuel Station 

PFAS in 

Surface Soil 

near the 

Facility 

Boundary 

PFAS in 

Subsurface 

Soil via soil 

infiltration 

and from 

leaks in 

drains, 

OWS, and 

underground 

piping

Human 

Activities

Precipitation/ 

Run-Off

Leaching/ 

Infiltration

Airborne Soil 

particulate

Surface Soil 

at AOI

Surface 

Water/ 

sediment3 Subsurface 

Soil

Shallow 

Groundwater

Source Release 

Mechanism Media Transport and Migration Media Exposure Routes

Inhalation of 

Dust

Ingestion

Ingestion

Ingestion

Ingestion

Human Receptors: 

Current/ Future

Flow-Chart Continues

Partial / Possible Flow

Flow-Chart Stops

Incomplete Pathway

Potentially Complete Pathway

Complete Pathway

Site Worker Construction Worker2 Resident1 Trespasser/ Recreational User

Site Worker Construction Worker2 Resident1 Trespasser/ Recreational User

/ /

LEGEND

/ /

/ / /

Figure 7-4

Preliminary Conceptual Site Model, Facility Boundary

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

/

/

/

/

/

/ /

/

/

Note: 

1. The residential receptor

refers to future residential

properties planned by the City

of Dallas.

2. No current active

construction at the facility.

/

/ / /

7-8
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 8-1

8. Summary and Outcome

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

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

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

8.1 SI Activities

The SI field activities were conducted from 22 to 24 March 2021 and consisted of utility clearance, 

direct push boring, soil sample collection, temporary monitoring well installation/plug and 

abandonment, grab groundwater sample collection, and land surveying. Field activities were 

conducted in accordance with the SI QAPP Addendum (AECOM, 2021b), except as previously 

noted in Section 5.8.

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

samples were collected and analyzed for a subset of PFAS by LC/MS/MS compliant with QSM

5.3 Table B-15 as follows. The 18 PFAS analyzed as part of the ARNG SI program are specified 

in Section 5.7 of this Report.

• 18 soil samples from 6 boring locations; 

• 6 grab groundwater samples from 6 temporary well locations; and

• 10 QA samples.

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

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 Section 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.

PFOA, PFOS, and PFBS were detected at the facility in soil and groundwater. PFOA, 

PFOS, and PFBS were detected both at the source areas, as well as at the facility 

boundary. PFOA in groundwater at AOI 1: Wash Rack and Fuel Station and the facility 

boundary exceeded the SL of 40 ng/L (individually). The detected concentrations of PFOS 

and PFBS in groundwater from all AOIs were below the SLs. Additionally, the detected 

concentrations of PFOA, PFOS, and PFBS in soil samples from all AOIs were below the 

SLs.

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.

Two PFAS release areas were removed from further consideration based on the 

groundwater and soil data collected during this SI: Flight Line Ram in AOI 2 and Former 

Firetruck Area in AOI 3. PFOA, PFOS, and PFBS were not detected in groundwater and/ 

or soil above the SLs in either of these areas; therefore, these areas pose no significant 

threat to human health or the environment. 
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 8-2

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.

A query of the Texas Water Development Board Submitted Drillers Reports Database

identified the presence of public supply wells and domestic wells downgradient from Grand

Prairie AASF. However, these wells range in depth from 80 ft bgs to 1158 ft bgs. Of these

wells, the shallowest well is an 80-foot-deep domestic well 4 miles away and the closest

well is a 2,084-foot-deep public supply well located within a mile of the facility.

Groundwater within the facility boundary is shallow ranging from 2.67 feet bgs to 13.08

feet bgs during the SI. Based on the depth of the downgradient wells and distance from

the facility, a TCRA is not recommended.

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

of a RI (if determined necessary).

The geological data collected as part of the SI indicate an overall permeable and

conductive environment, with soils mostly consisting of poorly-graded fine to very fine

sand and silt. Well graded sand with thin beds and lenses of gravel and mud clasts were

present along with intervals of clay and clayey sand ranging from a few inches to a few

feet thick.

These site observations are consistent with the SI QAPP which reported the general

stratigraphic sequence present throughout the TXARNG facility consists of Holocene and

Pleistocene alluvial terrace deposits overlaying the Cretaceous Eagle Ford Shale. The

upper soil horizons and alluvium have been disturbed locally by industrial development;

therefore, shallow surface and subsurface soils are composed of fill materials in some

areas. The lithology of sediments is primarily clay and silty clay. The clays are interspersed

with sporadic deposits of streambed sand and gravel (Geo-Marine, Inc [GMI], 2002).

During the SI, depth to water at Grand Prairie AASF ranged from approximately 2.67 to

13.08 feet bgs. Groundwater flows northward in the direction of Cottonwood Bay and

westward in the direction of the Diversion Channel. These geologic and hydrogeologic

observations inform development of technical approach for the RI.

5. 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 evaluation of groundwater and soil results in comparison to SLs, in

combination with the groundwater flow direction analysis, the results of the SI indicate that

ARNG activities may have contributed to the detected concentrations of PFOA, PFOS,

and PFBS at the facility, however, potential; releases from the adjacent property, as noted

in the Grand Prairie PA (AECOM, 2020), could have contributed to the higher

concentrations observed in the northeast corner of the property.

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

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

Detections of PFOA, PFOS, and PFBS in soil and groundwater underlying the facility and

the SL exceedance at the boundary indicate there is potentially a complete pathway

between the source and receptor.
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 8-3

8.3 Outcome 

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

exposure to receptors on facility resulting from historical DoD activities. Sample analytical 

concentrations collected during the SI were compared against the project SLs for PFOA, PFOS, 

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

data relative to the SLs is as follows:

• At AOI 1, PFOA in groundwater at the Wash Rack, Fuel Station, and downgradient of the 

Hazardous Materials Storage Building exceeded the SL of 40 ng/L at concentrations of 106 

ng/L and 94.4 ng/L, at locations AOI01-01 and AOI01-02, respectively. Based on the results 

of the SI, further evaluation of AOI 1 is warranted in the RI.

• At the facility boundary, PFOA in groundwater near the northeastern boundary exceeded 

the SL of 40 ng/L at a concentration of 369 ng/L at location GPF-01. Based on the results 

of the SI, further evaluation of the northeastern facility boundary is warranted in the RI. 

• At AOI 1 and GPF-01, detected concentrations of PFOS and PFBS in groundwater were 

below SLs.

• At AOI 2, AOI 3, and the eastern facility boundary (GPF-02) detected concentrations of 

PFOA, PFOS, and PFBS in groundwater were below SLs. 

• The detected concentrations of PFOA, PFOS, and PFBS in soil at all AOIs were below the 

SLs. 

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 receptors on facility caused 

by DoD activities at or adjacent to the facility.

Table 8-2 summarizes the rationale used to determine if an AOI should be considered for further 

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

is warranted in the RI for AOI 1: Wash Rack, AOI 1: Fuel Station, and Facility Boundary: GPF-01 

area.
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 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 

Wash Rack

Hazardous Materials 

Storage Building

N/A N/A

Fuel Station

2 Flight Line Ramp N/A

3 Former Firetruck 

Location

Facility 

Boundary 

GPF-01

GPF-02

Legend:

N/A = Not applicable 

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected

Table 8-2: Site Inspection Recommendations

AOI Description Rationale Future Action

1 

Wash Rack, 

Hazardous 

Materials 

Storage 

Building, and 

Fuel Station

Exceedances of SLs in groundwater at 

source areas. No exceedances of SLs in 

soil. 

Proceed to RI 

2 Flight Line 

Ramp

Detections in groundwater but no 

exceedances of SLs. No exceedances of 

SLs in soil.

No further action

3 Former Firetruck 

Location

Detections in groundwater but no 

exceedances of SLs. No exceedances of 

SLs in soil. 

No further action

Facility 

Boundary

GPF-01

(northeastern 

boundary)

Exceedances of SLs in groundwater at 

source areas. No exceedances of SLs in 

soil. 

Proceed to RI

GPF-02

(eastern 

boundary)

Detections in groundwater but no 

exceedances of SLs. No exceedances of 

SLs in soil.

No further action
Site Inspection Report

Grand Prairie Army Aviation Support Facility, Grand Prairie, Texas

AECOM 9-1

9. References

AECOM. 2018a. Final Site Inspection Programmatic Uniform Federal Policy-Quality Assurance 

Project Plan, Perfluorooctane Sulfonic Acid (PFOS) and Perfluorooctanoic Acid (PFOA) 

Impacted Sites ARNG Installations, Nationwide Contract No. W912DR-12-D-0014/

W912DR17F0192. 9 March.

AECOM. 2018b. Final Programmatic Accident Prevention Plan, Perfluorooctane Sulfonic Acid 

(PFOS) and Perfluorooctanoic Acid (PFOA) Impacted Sites ARNG Installations, Nationwide 

Contract No. W912DR-12-D-0014/W912DR17F0192. July.

AECOM. 2020. Final Preliminary Assessment Report, Grand Prairie Army Aviation Support 

Facility, Texas. July.

AECOM. 2021a. Final Site Safety and Health Plan, Grand Prairie Army Aviation Support Facility, 

Grand Prairie, Texas, Perfluorooctane Sulfonic Acid (PFOS) and Perfluorooctanoic Acid 

(PFOA) Impacted Sites ARNG Installations, Nationwide. March.

AECOM. 2021b. Final Site Inspection Uniform Federal Policy-Quality Assurance Project Plan 

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