FINAL

Site Inspection Report 

Army Aviation Support Facility #3 

Bates Field

Mobile, Alabama

Site Inspection for Perfluorooctanoic acid (PFOA), 

Perfluorooctanesulfonic acid (PFOS), Perfluorohexanesulfonic 

acid (PFHxS), Perfluorononanoic acid (PFNA), 

Hexafluoropropylene oxide dimer acid (HFPO-DA), and 

Perfluorobutanesulfonic acid (PFBS) at ARNG Installations, 

Nationwide

August 2023

Prepared for:

Army National Guard Bureau

111 S. George Mason Drive

Arlington, VA 22204

UNCLASSIFIED
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Table of Contents

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

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

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

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

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

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

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

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

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

2.2.3 Hydrology....................................................................................................2-3

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

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

2.2.6 Sensitive Habitat and Threatened/ Endangered Species.............................2-4

2.3 History of PFAS Use..............................................................................................2-4

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

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

3.1.1 Flight Ramp.................................................................................................3-1

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

3.2.1 Hangar Fire Suppression System................................................................3-1

3.2.2 Wash Rack..................................................................................................3-2

3.2.3 AFFF Storage Area .....................................................................................3-2

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

6.3.2 AOI 1 Groundwater Analytical Results.........................................................6-2
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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 ......................................................................................6-4

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

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

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

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

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

7.3.1 AOI 1...........................................................................................................7-3

7.3.2 AOI 2...........................................................................................................7-3

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

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

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

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

Appendix A Data Usability Assessment and Validation Reports

Appendix B Field Documentation

B1. Log of Daily Notice of Field Activities

B2. Sampling Forms

B3. 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, January 2022

Figure 2-5 Surface Water Features

Figure 3-1 Areas of Interest

Figure 5-1 Site Inspection Sample Locations

Figure 6-1 PFOA Detections in Soil

Figure 6-2 PFOS Detections in Soil

Figure 6-3 PFBS Detections in Soil

Figure 6-4 PFHxS Detections in Soil

Figure 6-5 PFNA Detections in Soil

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

Figure 6-7 PFHxS and PFNA Detections in Groundwater

Figure 7-1 Conceptual Site Model, AOI 1

Figure 7-2 Conceptual Site Model, AOI 2

Tables

Table ES-1 Screening Levels (Soil and Groundwater)

Table ES-2 Summary of Site Inspection Findings and Recommendations

Table 5-1 Site Inspection Samples by Medium

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

Elevations

Table 6-1 Screening Levels (Soil and Groundwater)

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

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

Table 6-4 PFOA, PFOS, PFBS, PFNA, and PFHxS Results in Deep Subsurface Soil

Table 6-5 PFOA, PFOS, PFBS, PFNA, and PFHxS Results in Groundwater

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

% percent

°C degrees Celsius

°F degrees Fahrenheit

μg/kg micrograms per kilogram

AASF Army Aviation Support Facility

AECOM AECOM Technical Services, Inc.

AFFF aqueous film-forming foam

ALARNG Alabama Army National Guard

AOI Area of Interest

ARNG Army National Guard

bgs below ground surface 

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act 

CoC chain of custody

CSM conceptual site model

DA Department of the Army

DoD Department of Defense

DOT Department of Transportation

DPT direct push technology

DQO data quality objective 

DUA data usability assessment

EDRTM Environmental Data Resources, Inc.TM

ELAP Environmental Laboratory Accreditation Program

EM Engineer Manual

FedEx Federal Express

FTA Fire Training Area

GPRS Ground Penetrating Radar Systems

GSA Geological Survey of Alabama

HDPE high-density polyethylene 

HFPO-DA hexafluoropropylene oxide dimer acid

IDW investigation-derived waste

ITRC Interstate Technology Regulatory Council

LC/MS/MS liquid chromatography with tandem mass spectrometry

MAWSS Mobile Area Water & Sewer System

MIL-SPEC military specification

MS/MSD matrix spike/matrix spike duplicate 

NELAP National Environmental Laboratory Accreditation Program

ng/L nanograms per liter

OSD Office of the Secretary of Defense

OWS oil-water separator

PA Preliminary Assessment 

PFAS per- and polyfluoroalkyl substances

PFBS perfluorobutanesulfonic acid

PFHxS perfluorohexanesulfonic acid
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PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

PID photoionization detector

PQAPP Programmatic UFP-QAPP

PVC polyvinyl chloride

QA quality assurance

QAPP Quality Assurance Project Plan

QC quality control

QSM Quality Systems Manual

SI Site Inspection

SL screening level

SOP standard operating procedure

TOC total organic carbon

TPP Technical Project Planning

UCMR 3 Third Unregulated Contaminant Monitoring Rule

UFP Uniform Federal Policy

US United States

USACE United States Army Corps of Engineers

USCG United States Coast Guard

USCS Unified Soil Classification System

USEPA United States Environmental Protection Agency

USFWS United States Fish and Wildlife Service

USGS United States Geological Survey
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Executive Summary

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

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

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

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

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

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

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

, and perfluorobutanesulfonic acid 

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

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

The PA identified two Areas of Interest (AOIs) where PFAS-containing materials may have been 

used, stored, disposed, or released historically (see Table ES-2 for locations). The objective of 

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

in the PA and determine whether further investigation is warranted, a removal action is required 

to address immediate threats, or no further action is required based on screening levels (SLs) for 

relevant compounds. This SI was completed at the Army Aviation Support Facility (AASF) #3

Bates Field in Mobile, Alabama and determined further investigation is warranted for AOI 1: Flight 

Ramp and AOI 2: Hangar Fire Suppression System, Wash Rack, and AFFF Storage Area. AASF 

#3 will also be referred to as the “facility” throughout this document.

AASF #3 is located at 9055 Tanner Williams Road, approximately 12 miles west of downtown 

Mobile, in Mobile County, Alabama. The facility is in the northeast-most section of the Mobile 

Regional Airport property. AASF #3 occupies approximately 35 acres and is used for the 

operation, maintenance, and repair of Alabama ARNG (ALARNG) rotary-winged aircraft. The 

facility houses a single hangar, administrative offices, and classrooms. According to ALARNG 

personnel, construction of the facility began in 1996 and was completed in 1999. Water and 

electric utilities are provided by the City of Mobile. 

The PA identified two AOIs for investigation during the SI phase. SI sampling results from the two

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

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

for AOI 1 and AOI 2. 

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

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

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

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

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

individual chemical of concern in the absence of other PFAS.
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Table ES-1: Screening Levels (Soil and Groundwater)

Analyteb

Residential

(Soil)

(μg/kg)a 

0-2 feet bgs

Industrial/ Commercial 

Composite Worker

(Soil)

(μg/kg)a 

2-15 feet bgs

Tap Water

(Groundwater)

(ng/L)a

PFOA 19 250 6

PFOS 13 160 4 

PFBS 1,900 25,000 601 

PFHxS 130 1,600 39

PFNA 19 250 6

Notes:

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

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

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

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

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

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

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

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

AOI Potential 

Release Area

Soil –

Source Area

Groundwater –

Source Area

Future 

Action

1 Flight Ramp Proceed 

to RI 

2

Hangar Fire 

Suppression System, 

Wash Rack, and 

AFFF Storage Area

Proceed 

to RI

Legend:

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected
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1. Introduction

1.1 Project Authorization

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

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

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

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

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

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

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

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

, and perfluorobutanesulfonic 

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

Support Facility (AASF) #3 Bates Field in Mobile, Alabama. AASF #3 is also referred to as the 

“facility” throughout this document. 

The SI project elements were performed in compliance with Comprehensive Environmental 

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

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

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

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

investigations. 

1.2 SI Purpose

A PA was performed at AASF #3 (AECOM Technical Services, Inc. [AECOM], 2020) that identified 

two Areas of Interest (AOIs) where PFAS-containing materials may have been used, stored, 

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

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

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

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

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

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

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

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

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

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

2.1 Facility Location and Description

AASF #3 is located at 9055 Tanner Williams Road, approximately 12 miles west of downtown 

Mobile, in Mobile County, Alabama. The facility occupies a 35-acre parcel of land along the west 

side of Tanner Williams Road, in the northeast-most section of the Mobile Regional Airport, within 

the airport property boundary. The latitude and longitude for the approximate center of the AASF 

are 30°42’21.06” N; 88°15’10.08” W. According to Alabama ARNG (ALARNG) personnel, 

construction of the facility began in 1996 and was completed in 1999. The site location is depicted 

on Figure 2-1. 

AASF #3 is used for the operation, maintenance, and repair of ALARNG rotary-winged aircraft. 

The facility includes one hangar and flight ramp and also houses administrative offices and 

classrooms. Roughly 50 percent (%) of AASF #3 is covered by developed or paved surfaces that 

are centrally located within the facility and are surrounded by maintained open fields. The AASF 

#3 flight ramp is connected to the Mobile Regional Airport via a taxiway located at the southwest 

corner of the facility. 

2.2 Facility Environmental Setting

AASF #3 is located within in the Alluvial-Deltaic Plain district of the Coastal Plain physiographic 

province. The Alluvial-Deltaic Plain is characterized by shallow topographic relief with poorly 

defined drainage patterns. AASF #3 sits at an elevation of approximately 200 feet above mean 

sea level. The land surface is relatively flat across the facility, with some constructed berms and 

drainage features present throughout. The facility and surrounding topography generally slope to 

the northwest, with the grade steepening off-facility towards Pierce Creek (Figure 2-2). The facility 

lies within the Southern Coastal Plain ecoregion, which is characterized by low-lying plains, 

swampy areas, and bottomlands; it is drained by meandering, low-gradient, and sandy bottom 

streams (US Geological Survey [USGS], 2002).

Land use in the vicinity of AASF #3 includes residential and commercial areas to the north and 

east, and the Mobile Regional Airport to the south and west. The north end of the Mobile Regional 

Airport runway is connected to the southwest corner of AASF #3 by a taxiway. A US Coast Guard 

(USCG) facility, also on the Mobile Airport property, is located approximately 0.6, miles southeast 

of the AASF.

2.2.1 Geology

Near-surface geology in the vicinity of AASF #3 consists of undifferentiated Holocene and 

Pleistocene age alluvial, coastal, and low terrace deposits characterized by white, gray, orange, 

and red very fine- to coarse-grained sand with gravel and gray and orange sandy clay in some 

places (Geological Survey of Alabama [GSA], 1972). Throughout most of the area, these sands 

are less than 50 feet thick; however, in the Mobile River floodplain, alluvial deposits are as much 

as 150 feet thick (USGS, 2019). 

Stratigraphically, the Pliocene age Citronelle Formation underlies the undifferentiated Holocene 

and Pleistocene units throughout the region; however, the Citronelle Formation is the recognized 

surficial unit present at AASF #3, where the alluvial deposits are absent (GSA, 1971). The 

Citronelle formation is characterized by moderate-reddish-brown, deeply weathered, fine to very 

coarse quartz sand with varicolored, typically mottled, lenticular beds of clay and clayey gravel. 

Limonite pebbles and lenses of limonite-cemented sand occur locally in weathered exposures. 

Gravel found in the Citronelle formation is composed of chert and quartz pebbles. (USGS, 2019). 
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The undifferentiated Miocene Series unconformably underlies the Citronelle Formation and is 

characterized by moderate-yellowish-orange, thinly bedded to massive, fine to coarse sand, 

gravelly sand, thin-bedded to massive clay, and sandy clay. Limonite pellets occur in places along 

clay sand contacts. Gravel in the Miocene Series is composed of quartz and chert granules and 

pebbles (USGS, 2019).

The Miocene age Pensacola Clay Formation conformably underlies the undifferentiated Miocene 

Series and is characterized by greenish-gray to light olive-gray, slightly calcareous, slightly 

micaceous silty to sandy clay containing beds and lenses of sand (GSA, 1985). Geologic units 

are depicted on Figure 2-3.

Direct push soil borings were completed during the SI at depths ranging between 30 to 45 feet 

below ground surface (bgs). The soil borings generally encountered poorly graded sand and 

sandy silt. Observed sands were generally fine-grained. Silty sand was encountered within the 

upper 10 and 20 feet of two boring locations in the northern portion of the facility. Additionally, 

isolated layers of lean clay were observed in borings located in the southwestern portion of the 

facility. Based on the depths, thicknesses, and intermittent frequency of the encountered clay 

layers, the clay layers appear to be lenticular. These boring observations are consistent with the 

Citronelle Formation; which is described as moderate-reddish-brown, deeply weathered, fine to 

very coarse quartz sand with varicolored, typically mottled, lenticular beds of clay, and is the 

recognized surficial formation present at AASF #3.

A sample for grain size analysis was collected at one location where a shift to fine grained 

materials was observed, AOI01-01 (28 to 30 feet bgs), and was analyzed via American Society 

for Testing and Materials (ASTM) Method D-422. The results indicate that the soil sample is 

comprised primarily of silt (56.35%) and clay (32.56%), with the remaining fraction comprised 

mostly of fine sand (10.51%). Boring logs are presented in Appendix E, and grain size results 

are presented in Appendix F.

2.2.2 Hydrogeology

The principal groundwater-bearing units in Mobile County are the permeable sands of the 

Miocene Series and overlying Citronelle Formation. Hydrogeologically, these units are referred to 

collectively as the Miocene-Pliocene Aquifer. Individual sand beds within the aquifer may be up 

to 50 to 100 feet thick and are separated by clay layers that can be equal in thickness (GSA, 

1972). A widespread confining unit is not recognized within the aquifer, as the sand and clay beds 

vary unpredictably in many areas. As a result, only locally confining clay beds are expected to be 

present throughout the aquifer; this is supported by observations from the SI that found clay layers 

were encountered infrequently and at various depths and are, therefore, considered to be 

lenticular and not consistent with a large-scale confining unit.

High-capacity wells tapping the aquifer in Mobile County target the prominent sands and generally 

range in depth from 150 to 800 feet. Wells requiring lower capacity likely do not reach these sands 

because of the availability of adequate supplies at shallower depths (GSA, 1972). Groundwater 

features surrounding the facility are shown in Figure 2-3. 

Groundwater in the vicinity of AASF #3 was anticipated to be encountered at depths of 

approximately 20 to 30 feet bgs. Synoptic groundwater level measurements collected during the 

SI were found to range between 22.68 to 34.63 feet bgs. Groundwater elevations, calculated 

using depth to groundwater measurements and the surveyed ground surface elevation, were 

generally higher in the north-northwest investigation area and decreased towards the southsoutheast, with the exception of elevated groundwater measured in the southern portion of the 

facility. As a result, the SI findings show an overall southeasterly groundwater flow direction over 

much of the facility (Figure 2-4). In the northern portion of the facility, a retention pond is situated 

in the vicinity of temporary monitoring wells AOI01-01 and MOB-01. The retention pond appears 
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to artificially elevate the groundwater levels through groundwater mounding, potentially causing 

groundwater to flow radially from the pond. In the southern portion of the facility, elevated 

groundwater was observed at AOI01-03. The boring log from this location shows lean clay was 

observed from 32.5 feet bgs to at least the terminal boring depth. It is possible that this clay is the 

same clay layer observed at a higher elevation in adjacent boring AOI01-02, in which case the 

dipping clay surface may form a localized basin that is creating perched groundwater conditions

in this part of the facility. As a result of these influences on the localized groundwater elevations 

and flow directions on-facility, the inferred regional groundwater flow direction in the surrounding 

vicinity of AASF #3 must still be assumed from topography and surface water drainage patterns 

and is considered to be to the southwest. 

Drinking water at the facility and surrounding area is supplied by the Mobile Area Water & Sewer 

System (MAWSS), which sources all of its drinking water from Big Creek Lake (MAWSS, 2022). 

According to the USGS National Water Information System Mapper, the only wells identified in a 

4-mile radius of the facility were 15 inactive USGS wells. A recent review of available well records

on the Geological Survey of Alabama Groundwater Assessment Program’s Water Well Finder

indicated the presence of up to 26 wells within a 1-mile radius of the facility (GSA, 2022). The

wells are located to the northeast and southeast of AASF #3 and were identified as domestic,

industrial, and observation use. The nearest identified well is located approximately 1,500 feet

northeast of the facility. All of the identified wells are within the MAWSS public drinking water

supply area, so it is not known if any are still used as a potable source. Drinking water at AASF

#3 is provided by MAWSS, which sources all drinking water from Big Creek Lake, located

approximately 3 miles northwest of the facility.

2.2.3 Hydrology 

AASF #3 lies within the Escatawpa River Basin, just west of the drainage divide of the Escatawpa 

and Mobile River Basins, and is part of the Pierce Creek-Big Creek watershed. Surface water in 

the vicinity of AASF #3 drains to the northwest, towards Pierce Creek, located 0.5 miles northwest 

of the facility. Pierce Creek flows approximately 7 miles southwest and drains into Big Creek 

downstream of Big Creek Lake, which is the main source of drinking water for almost 70% of 

Mobile County (MAWSS, 2019). Big Creek continues to flow southwest into Mississippi, where it 

empties into the Escatawpa River. Surface water features surrounding the facility are shown in 

Figure 2-5. 

Drainage at AASF #3 is controlled by sheet flow and several shallow drainages that direct surface 

runoff to the northwest. A retention pond is located at the northwest corner of the facility that, per 

ALARNG personnel, collects all on-facility runoff as well as some runoff from parts of the nearby 

airport property to the west. The retention pond also receives overflow from the facility’s oil-water 

separator (OWS) during upset conditions. Runoff captured by the retention pond either 

evaporates or infiltrates to groundwater, as there is no outflow from the pond. 

2.2.4 Climate 

Alabama’s climate is humid and subtropical. The average temperature in Mobile is 67.25 degrees 

Fahrenheit (°F), with an average high of 77.5 °F and an average low of 57 °F. Rainfall in Alabama 

usually is abundant and distributed throughout the year. Mobile receives an average of 66.22 

inches of rain per year (World Climate, 2022). 

2.2.5 Current and Future Land Use

The ALARNG AASF #3 facility is within the Mobile Regional Airport property and is used for the 

operation, maintenance, and repair of ALARNG rotary-winged aircraft. Properties surrounding 

AASF #3 primarily consist of the Mobile Regional Airport to the west and south, including a USCG 
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facility located on the airport property southeast of the AASF. Residential areas are located 

immediately north and east of AASF #4, across Tanner Williams Road, and a recreational park is 

immediately east of the facility. Commercial properties exist southeast of the facility and 

undeveloped land is located to the west and southwest, beyond the airport. Reasonably 

anticipated future land use is not expected to change from the current land use.

2.2.6 Sensitive Habitat and Threatened/ Endangered Species 

The following amphibians, birds, clams, insects, fish, mammals, and reptiles are federally 

endangered, threatened, proposed, and/ or are listed as candidate species in Mobile County, 

Alabama (US Fish and Wildlife Service [USFWS], 2022). 

• Amphibians: Dusky gopher frog, Rana sevosa (endangered)

• Birds: Red knot, Piping Plover, Calidris canutus rufa (threatened), Charadrius melodus 

(threatened), Wood stork, Mycteria americana (threatened), Eastern Black rail, Laterallus 

jamaicensis ssp. jamaicensis (threatened)

• Clams: Southern clubshell, Pleurobema decisum (endangered), Inflated heelsplitter, 

Potamilus inflatus (threatened)

• Insects: Monarch butterfly, Danaus plexippus (candidate)

• Fish: Gulf sturgeon, Acipenser oxyrinchus (=oxyrhynchus) desotoi (threatened), Alabama 

sturgeon, Scaphirhynchus suttkusi (endangered)

• Mammals: West Indian Manatee, Trichechus manatus (threatened) 

• Reptiles: Alligator snapping turtle, Macrochelys temminckii (proposed), Loggerhead sea 

turtle, Caretta caretta (threatened), Gopher tortoise, Gopherus polyphemus (candidate), 

Eastern indigo snake, Drymarchon corais couper (threatened), Kemp's ridley sea turtle, 

Lepidochelys kempii (endangered), Hawksbill sea turtle, Eretmochelys imbricata 

(endangered), Black pinesnake, Pituophis melanoleucus lodingi (threatened), Alabama redbellied turtle, Pseudemys alabamensis (endangered), Leatherback sea turtle, Dermochelys 

coriacea (endangered)

2.3 History of PFAS Use

Four potential release areas (grouped into two AOIs) where AFFF may have been used or 

released historically were identified at AASF #3 (AECOM, 2020). PFAS-containing materials were 

potentially released to surface soil within the boundary of AASF #3 through equipment discharge, 

accidental leaks and spills, and any potential undocumented fire suppression system testing. The 

potential release areas were grouped into two AOIs based on proximity to one another and 

presumed groundwater flow. These areas include:

• AOI 1: Flight Ramp

• AOI 2: Hangar Fire Suppression System, Wash Rack, and the AFFF Storage Area located 

east of the Flight Ramp

Foam-containing firefighting equipment was known to have been present at the facility as early 

as 1999 until present. AFFF Tri-MaxTM 30 mobile extinguisher units were staged along the Flight 

Ramp southwest of the hangar building. The Tri-MaxTM 30 units were maintained by a contractor. 

Prior to removal of the Tri-MaxTM 30 units around 2008, some of the units were discharged on the 

southeast portion of the Flight Ramp. 
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AECOM 2-5

The AASF #3 hangar overhead fire suppression system is equipped with an 800-gallon AFFF tank 

filled with Chemguard 3% AFFF. The current system was installed from 2016 to 2018 and replaced 

the AFFF system that was part of the original hangar construction in 1999. Prior to replacement, 

ALARNG noted that the original overhead dispensing nozzles were rusted, the bladder system 

within the AFFF concentrate tank was found to be ruptured, and the shutoff valve/backflow 

preventer had been installed backward. Information regarding a full-scale test of the original 

suppression system is not available. Two poly 55-gallon drums containing Chemguard 3% left 

over from the system hangar fire suppression system upgrade are stored on secondary 

containment in the chemical storage building. Descriptions of AOI 1 and AOI 2 are further 

presented in Section 3. 
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Army Aviation Support Facility #3, Mobile, Alabama

AECOM 2-12

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Site Inspection Report

Army Aviation Support Facility #3, Mobile, Alabama

AECOM 3-1

3. Summary of Areas of Interest 

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

disposed, or released historically. Based on the PA findings, three potential release areas were 

identified at AASF #3 and grouped into two AOIs (AECOM, 2020). A fourth potential release area, 

AFFF Storage Area, was added after the PA was finalized and grouped into AOI 2. The potential 

release areas are shown on Figure 3-1.

Two potential off-facility sources of PFAS adjacent to AASF #3, not under the control of the 

ALARNG, were identified during the PA (AECOM, 2020). These potential off-facility sources 

include the USCG facility (adjacent to the southeast and also within the Mobile Regional Airport) 

and all other hangars, ramps, taxiways, runways, and facilities located on the Mobile Regional 

Airport property not associated with ALARNG activity. According to interviewed ALARNG 

personnel, the hangar at the USCG facility may be equipped with an AFFF dispensing system, 

and an AFFF release may have occurred between 2014 and 2015. Additionally, the ALARNG 

personnel stated some hangars at the Mobile Regional Airport are suspected to be equipped with 

AFFF suppression systems; however, the use and storage of AFFF at the Mobile Regional Airport 

are unknown. The USCG facility and Mobile Airport are also shown on Figure 3-1 as a potential 

adjacent sources; however, it must be noted that this SI did not evaluate off-facility sources, and 

these locations are shown for informational purposes only. 

3.1 AOI 1 

AOI 1 consists of one potential release area. The potential release area is described below.

3.1.1 Flight Ramp

AOI 1 is the Flight Ramp located along the western portion of the facility. According to ALARNG 

personnel with knowledge of the facility dating back to 2002, approximately 10 AFFF Tri-MaxTM

30 mobile extinguisher units were historically (until about 2008) staged along the Flight Ramp

southwest of the hangar building. The Tri-MaxTM 30 units were maintained by a contractor, and 

ALARNG did not have copies of the disposal documents or knowledge of the type and where the 

Tri-MaxTM 30 units were transported and disposed. However, ALARNG personnel did indicate that 

prior to removal of the Tri-MaxTM 30 units around 2008, at least some of these units were 

discharged on the southeast portion of the Flight Ramp. Currently, dry chemical Purple K units 

are used on the ramp. It was noted during the PA that the ramp is not constructed with storm 

drains. Surface water drainage from the Flight Ramp appears to flow northwest via sheet flow or

via shallow drainage on the west side of the ramp to the retention pond located at the northwest 

corner of the facility property. 

3.2 AOI 2

AOI 2 consists of three potential release areas, as described below. Any releases at AOI 2 could 

have occurred on the hangar floor or on the pavement of the Wash Rack and AFFF storage area. 

It is possible AFFF may have infiltrated into the subsurface soil via joints or cracks in the floor slab 

and pavement or run off to the surrounding grassy areas. 

3.2.1 Hangar Fire Suppression System

The AASF #3 hangar building contains an overhead fire suppression system equipped with an 

800-gallon AFFF tank filled with Chemguard 3% AFFF. Two 60,000-gallon water tanks located 

approximately 300 feet northeast of the hangar are used as the water supply for the AFFF system. 
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Army Aviation Support Facility #3, Mobile, Alabama

AECOM 3-2

The current system was installed as part of a state-wide effort to upgrade fire suppression systems 

and was constructed from 2016 to 2018, replacing the AFFF system that was part of the original 

hangar construction in 1999. During the PA interviews, ALARNG personnel indicated that an 

unknown type of AFFF was used in the original suppression system. It is unknown where the 

components and concentrate from the original system were taken. Information regarding a fullscale test of the original suppression system could not be ascertained. According to the ALARNG 

personnel interviewed, a full-scale test of the new system was not conducted, and the system has

not been triggered. During the visual inspection, some corrosion and rust staining were observed 

at the floor drain beneath the current AFFF concentrate tank. 

Floor and trench drains in the hangar building drain to the above-ground OWS, which discharges 

to the MAWSS municipal sanitary sewer system. An overflow basin located beside the OWS 

receives flow during upset conditions when the OWS is not functioning properly or is overwhelmed 

during significant rainfall events. According to ALARNG personnel, recent dye testing indicated 

that the overflow basin drains to the retention pond. 

3.2.2 Wash Rack

The Wash Rack is located southeast of the hangar building and is used to wash aircraft. According 

to ALARNG personnel with knowledge of the property dating back to 2002, annual fire training 

using a burn barrel and Purple K units was conducted at the Wash Rack. ALARNG personnel 

stated that AFFF was not used as part of these fire training exercises. As identified earlier, 

approximately 10 AFFF Tri-MaxTM 30 units were historically staged along the Flight Ramp located 

southwest of the hangar building. Although ALARNG personnel stated that only Purple K units 

were used in fire training, there is the possibility that the AFFF Tri-MaxTM 30 units may have been 

used for fire training, or that some of the AFFF known to have been discharged on the Flight 

Ramp drained to the Wash Rack. The Wash Rack is sloped on all sides towards one drain in the 

center of the Wash Rack. The Wash Rack drains to the OWS and combines with drainage from 

the hangar, then drains to the sanitary sewer system, or to the overflow basin and retention pond

in upset conditions.

3.2.3 AFFF Storage Area

During the PA site visit, ALARNG personnel noted two poly 55-gallon drums containing 

Chemguard 3% AFFF that are currently staged on secondary containment, within a chemical 

storage building southeast of the hangar and Wash Rack. These drums contain AFFF concentrate 

left over by a contractor after the 800-gallon tank for the overhead suppression system had been 

filled to capacity. At the time of the visual inspection, no evidence of drum leaks or spills were 

apparent. No floor drains were evident in the storage building.
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Site Inspection Report

Army Aviation Support Facility #3, Mobile, Alabama

AECOM 4-1

4. Project Data Quality Objectives

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

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

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

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

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

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

AOIs.

4.1 Problem Statement

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

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

SLs are presented in Section 6.1 of this report.

4.2 Information Inputs

Primary information inputs included:

• The PA for AASF #3 (AECOM, 2020);

• Analytical data collected as part of ALARNG drinking water at the facility (ALARNG, 2017);

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

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

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

parameters measured at the time of sampling.

4.3 Study Boundaries

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

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

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

owner(s). The SI scope was bounded vertically by the observed depths of the surficial groundwater 

table. Temporal boundaries of the study were limited by seasonal conditions present during the Winter 

2022 field work.

4.4 Analytical Approach

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

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

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

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

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

4.5 Data Usability Assessment

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

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

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

methods, the assessment determines whether project execution and the resulting data have met 
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AECOM 4-2

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 decisionmaking (DoD, 2019a; DoD, 2019b; USEPA, 2017).

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

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

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

requirements of the SI QAPP Addendum (AECOM, 2021). 
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Army Aviation Support Facility #3, Mobile, Alabama

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 Uniform Federal Policy-Quality Assurance Project Plan 

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

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

• Final Preliminary Assessment Report, AASF #3 Bates Field, Mobile, Alabama dated 

September 2020 (AECOM, 2020);

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

AASF #3 Bates Field, Mobile, Alabama dated November 2021 (AECOM, 2021); and

• Final Site Safety and Health Plan, AASF #3 Bates Field, Mobile, Alabama dated January 

2022 (AECOM, 2022).

The SI field activities were conducted from 18 to 25 January 2022 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, 2021).

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

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

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

• Twenty-four (24) soil samples from ten (10) locations; 

• Seven (7) grab groundwater samples from seven (7) temporary wells; and

• Sixteen (16) quality assurance (QA)/quality control (QC) samples.

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

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

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

in Appendix B1. Sampling forms are provided in Appendix B2. Land survey data are provided 

in Appendix B3. Additionally, a photographic log of field activities is provided in Appendix C. 

5.1 Pre-Investigation Activities

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

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

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

5.1.1 Technical Project Planning

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

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

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

collection plan. The process encourages stakeholder involvement in the SI, beginning with 

defining overall project objectives, including DQOs, and formulating a sampling approach to 

address the AOIs identified in the PA. 
AECOM 5-2

Site Inspection Report

Army Aviation Support Facility #3, Mobile, Alabama

A combined TPP Meeting 1 and 2 was held on 22 September 2021, prior to SI field activities. The 

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

stakeholders for this SI include the ARNG G-9, ALARNG, and USACE. 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, 2021). 

A TPP Meeting 3 was held on 26 July 2023 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 

Both AECOM and their drilling contractor, Walker-Hill Environmental, contacted Alabama 811 onecall utility clearance contractor prior to mobilization to notify them of intrusive work. Because 

Alabama 811 locators do not locate private utilities, such as those belonging to AASF #3, AECOM 

contracted Ground Penetrating Radar Systems, LLC (GPRS) to perform utility clearance for 

private utilities at all boring locations. GPRS performed the utility clearance under the oversight 

of the AECOM field team on 19 January 2022 using industry standard methods in addition to 

ground-penetrating radar. Additionally, the first 5 feet of the direct-push borings were advanced 

using hand augering methods to visually verify utility clearance in the shallow subsurface where 

utilities would typically be encountered.

5.1.3 Source Water and Sampling Equipment Acceptability

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

acceptable for use prior to the start of field activities. Potable water samples from two sources at 

AASF #3 were collected on 17 November 2021, prior to mobilization, and analyzed by LC/MS/MS 

compliant with QSM 5.3 Table B-15. The results of the decontamination water sample are 

provided in Appendix F. A discussion of the results is presented in the DUA (Appendix A). 

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

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

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

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

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

regarding the allowable materials within the sampling environment. 

5.2 Soil Borings and Soil Sampling

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

Addendum (AECOM, 2021). 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 5 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 observed groundwater table, and one subsurface soil sample at 

the mid-point between the surface and the groundwater table. If groundwater was not 

encountered above 30 feet bgs, the intermediate sample was collected from the 13- to 15-foot 

bgs interval.
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AECOM 5-3

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

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

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

Observations and measurements were recorded on boring logs (Appendix E) and in a nontreated 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.

Direct push soil borings were completed during the SI at depths ranging between 30 to 45 feet 

bgs. The soil borings generally encountered poorly graded sand and sandy silt. Observed sands 

were generally fine-grained. Silty sand was encountered within the upper 10 and 20 feet of two 

boring locations in the northern portion of the facility, AOI01-01 and MOB-01, respectively. 

Additionally, isolated layers of lean clay were observed below 25 feet bgs in several borings 

located in the southwestern portion of the facility. Based on the depths, thicknesses, and 

intermittent frequency of the encountered clay layers in the soil borings, the clay layers appear to 

be lenticular. Red and brown colored soils were generally encountered in the upper portion of the 

soil borings, suggesting a higher degree of weathering, while white, pink, and yellow soils were 

generally encountered in the lower portions of the soil borings. These results and facility 

observations are consistent with the Citronelle Formation, which is the recognized surficial unit 

present at the facility, and is described as moderate-reddish-brown, deeply weathered, fine to 

very coarse quartz sand with varicolored, typically mottled, lenticular beds of clay.

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

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

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

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

carbon (TOC) (USEPA Method 9060A), pH (USEPA Method 9045D), and grain size (ASTM 

Method D-422) in accordance with the SI QAPP Addendum (AECOM, 2021).

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

as the accompanying samples. Matrix spike (MS)/MS duplicate (MSD) samples were collected at 

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

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

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

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

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

The boreholes were converted to temporary wells, as described in Section 5.3, and then 

subsequently abandoned in accordance with the SI QAPP Addendum (AECOM, 2021) at the 

completion of sampling activities. The ground surface at each boring location was restored to 

match surrounding cover.

5.3 Temporary Well Installation and Groundwater Grab Sampling

Temporary wells were installed in seven boring locations using a GeoProbe® 7822DT dual-tube 

sampling system. Once the borehole was advanced to the desired depth, a temporary well was 

constructed of a 5-foot section 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.

Sufficient time was allowed for groundwater accumulation in the temporary wells before 

proceeding with collection of groundwater samples. Wells were purged using a peristaltic pump 

or bladder pump with PFAS-free HDPE tubing to remove sediment to the extent reasonable in an 

effort to minimize the turbidity of the samples. The temporary wells were purged at a rate 
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Army Aviation Support Facility #3, Mobile, Alabama

AECOM 5-4

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

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

sampling form (Appendix B2) before each grab sample was collected. Each sample was 

collected into laboratory-supplied PFAS-free HDPE bottles and labeled using a PFAS-free marker 

or pen. Additionally, a subsample of each groundwater sample was collected in a separate 

container, and a shaker test was completed to identify if there were any foaming. No foaming was 

noted in any of the groundwater samples. Samples were packaged on ice and transported via 

FedEx under standard CoC procedures to the laboratory and analyzed by LC/MS/MS compliant 

with QSM 5.3 Table B-15 in accordance with the SI QAPP Addendum (AECOM, 2021).

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

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

for the same parameters as the accompanying samples. Because non-dedicated sampling 

equipment was required due to the use of a bladder pump at several locations, equipment rinsate 

blanks were collected at a rate of 5% and analyzed for the same parameters as the groundwater 

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.

Following well surveying (described below in Section 5.5), temporary wells were abandoned in 

accordance with the SI QAPP Addendum (AECOM, 2021) by removing the PVC and backfilling 

the hole with bentonite-cement grout. Upon completion of well abandonment, the ground surface 

at each location was patched to match existing surrounding conditions. Temporary wells were 

installed in grass areas to avoid disturbing concrete or asphalt.

5.4 Synoptic Water Level Measurements

A synoptic groundwater gauging event was performed on 25 January 2022. Groundwater level 

measurements were collected from the temporary monitoring wells. Water level measurements 

were taken from the northern side of the well casing. Groundwater was measured between 22.68 

to 34.63 feet bgs. A groundwater flow contour map is provided in Figure 2-4. Groundwater 

elevation data are provided in Table 5-2.

5.5 Surveying

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

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

data from the newly installed wells on the facility were collected on 25 January 2022 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 B3.

5.6 Investigation-Derived Waste

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

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

accordance with the SI QAPP Addendum (AECOM, 2021) and with the DA Guidance for 

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

Soil IDW (i.e., soil cuttings) were generated during the SI activities from the ten soil boring 

locations. No soil IDW was generated at the surface soil sample locations. Due to the minimal 

amount of soil IDW generated, all soil IDW were containerized in one labeled, 55-gallon 

Department of Transportation (DOT)-approved steel drums and stored on the east-central portion 
Site Inspection Report

Army Aviation Support Facility #3, Mobile, Alabama

AECOM 5-5

of the facility (near AOI02-03). Based on laboratory results, containerized soil cuttings will be 

managed and disposed of off-facility by ARNG, under a separate contract held by EA Engineering, 

Science, and Technology, Inc. (EA). Specifics on the disposal of solid IDW will be addressed in 

an IDW Treatment Memorandum submitted by EA.

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

containerized in two labeled, 55-gallon DOT-approved steel drums and stored next to the soil IDW 

drums. Based on laboratory results, ARNG will manage and dispose of the liquid IDW off-facility 

under a separate contract held by EA. Specifics on the disposal of liquid IDW will be addressed 

in an IDW Treatment Memorandum submitted by EA.

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

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

activities were disposed of at a licensed solid waste landfill.

5.7 Laboratory Analytical Methods

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

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

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

Army Aviation Support Facility #3, Mobile, Alabama

AECOM 5-6

THIS PAGE INTENTIONALLY BLANK
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, AASF #3 Bates Field, Mobile, Alabama

Sample Identification

Sample

Collection 

Date/Time

Sample Depth 

(feet bgs)

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

Comments

AOI01-01-SB-00-02 1/22/2022 13:40 00-02 x x x

AOI01-01-SB-00-02-D 1/22/2022 13:40 00-02 x x x Duplicate

AOI01-01-SB-00-02-MS 1/22/2022 13:40 00-02 x x x MS/MSD

AOI01-01-SB-00-02-MSD 1/22/2022 13:40 00-02 x x x MS/MSD

AOI01-01-SB-10-12 1/23/2022 9:12 10-12 x

AOI01-01-SB-10-12-MS 1/23/2022 9:12 10-12 x MS/MSD

AOI01-01-SB-10-12-MSD 1/23/2022 9:12 10-12 x MS/MSD

AOI01-01-SB-22-24 1/23/2022 9:15 22-24 x

AOI01-01-SB-28-30 1/23/2022 9:20 28-30 x

AOI01-02-SB-00-02 1/23/2022 10:30 00-02 x

AOI01-02-SB-13-15 1/23/2022 10:40 13-15 x

AOI01-02-SB-30-32 1/24/2022 16:30 30-32 x

AOI01-03-SB-00-02 1/23/2022 11:24 00-02 x

AOI01-03-SB-13-15 1/23/2022 13:30 13-15 x

AOI01-03-SB-30-32 1/23/2022 14:00 30-32 x

AOI02-01-SB-00-02 1/24/2022 9:00 00-02 x

AOI02-01-SB-13-15 1/24/2022 9:25 13-15 x

AOI02-01-SB-33-35 1/24/2022 9:38 33-35 x

AOI02-02-SB-00-02 1/24/2022 9:55 00-02 x x x

AOI02-02-SB-00-02-D 1/24/2022 9:55 00-02 x Duplicate

AOI02-02-SB-13-15 1/24/2022 12:00 13-15 x

AOI02-02-SB-33-35 1/24/2022 12:35 33-35 x

AOI02-03-SB-00-02 1/23/2022 12:30 00-02 x

AOI02-03-SB-13-15 1/23/2022 14:55 13-15 x

AOI02-03-SB-33-35 1/24/2022 15:30 33-35 x

AOI02-04-SB-00-02 1/23/2022 14:20 00-02 x

MOB-01-SB-00-02 1/22/2022 10:50 00-02 x

MOB-01-SB-13-15 1/22/2022 11:40 13-15 x

MOB-01-SB-28-30 1/22/2022 12:30 28-30 x

MOB-02-SB-00-02 1/22/2022 14:05 00-02 x

MOB-03-SB-00-02 1/23/2022 11:00 00-02 x

MOB-03-SB-00-02-D 1/23/2022 11:00 00-02 x Duplicate

Soil Samples

AECOM 5-7
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, AASF #3 Bates Field, Mobile, Alabama

Sample Identification

Sample

Collection 

Date/Time

Sample Depth 

(feet bgs)

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

Comments

AOI01-01-GW 1/23/2022 16:17 NA x

AOI01-01-GW-D 1/23/2022 16:17 NA x Duplicate

AOI01-02-GW 1/25/2022 10:51 NA x

AOI01-03-GW 1/24/2022 12:27 NA x

AOI02-01-GW 1/25/2022 9:23 NA x

AOI02-02-GW 1/24/2022 16:02 NA x

AOI02-02-GW-MS 1/24/2022 16:02 NA x MS/MSD

AOI02-02-GW-MSD 1/24/2022 16:02 NA x MS/MSD

AOI02-03-GW 1/25/2022 12:24 NA x

MOB-01 1/23/2022 9:42 NA x

MOB-DECON-01 11/17/2021 11:05 NA x DECON

MOB-DECON-02 11/17/2021 10:30 NA x DECON

MOB-FRB-01 1/25/2022 13:15 NA x FRB

MOB-ERB-01 1/22/2022 14:44 NA x ERB

MOB-ERB-02 1/25/2022 13:30 NA x ERB

MOB-ERB-03 1/25/2022 9:40 NA x ERB

Notes:

ASTM = American Society for Testing and Materials

bgs = below ground surface

ERB = equipment rinsate blank

FRB = field reagent blank

LC/MS/MS = Liquid Chromatography Mass Spectrometry

MS/MSD = matrix spike/ matrix spike duplicate

QSM = Quality Systems Manual

TOC = total organic carbon

USEPA = United States Environmental Protection Agency

Quality Control Samples

Groundwater Samples

AECOM 5-8
Table 5-2

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

Site Inspection Report, AASF #3 Bates Field, Mobile, Alabama

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)

Dept

Wa

(feet 

AOI01-01 30 21-26 206.04 204.88 23.84 22

AOI01-02 43 38-43 209.19 208.29 34.13 33AOI01-03 33 28-33 210.82 210.43 30.05 29

MOB-1 35 30-35 207.52 207.00 30.35 29

AOI02-01 40 35-40 209.90 209.37 34.65 34AOI02-02 40 35-40 211.25 209.85 35.28 33AOI02-03 45 40-45 211.21 210.64 35.20 34

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

12

AECOM 
THIS PAGE INTENTIONALLY BLANK

COM 5-10
?!

?!

?!

?!

?!

?!

"S

?!

"S

"S

AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

AOI02-04

MOB-01

MOB-02

MOB-03

Legend

?! Soil and Groundwater Sample

"S Surface Soil Sample

Facility Boundary

Surface Water Flow Direction

Groundwater Flow Direction

CLIENT

REVISED

SCALE

ARNG

GIS BY

CHK BY

MS

VG

9/1/2022

9/1/2022

Site Inspection at Bates Field AASF #3, AL

9/1/2022 ­ Figure 5-1 PM CM 9/1/2022

12420 Milestone Center Drive

Germantown, MD 20876

Site Inspection Sample Locations

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

and the GIS User Community

1:3,600

0 150 300 600

Feet

PROJECT

AECOM 5-11
Site Inspection Report

Army Aviation Support Facility #3, Mobile, Alabama

AECOM 5-12

THIS PAGE INTENTIONALLY BLANK
Site Inspection Report

Army Aviation Support Facility #3, Mobile, Alabama

AECOM 6-1

6. Site Inspection Results 

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

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

through Section 6.4. Table 6-2 through Table 6-5 present results in soil or groundwater for the 

relevant compounds. Tables that contain all results are provided in Appendix F, and the 

laboratory reports are provided in Appendix G. 

6.1 Screening Levels 

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

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

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

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

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

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

6-1 below.

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

Analyteb 

Residential

(Soil)

(μg/kg)a 

0-2 feet bgs

Industrial/ 

Commercial 

Composite 

Worker

(Soil)

(μg/kg)a 

2-15 feet bgs

Tap Water

(Groundwater)

(ng/L)a

PFOA 19 250 6 

PFOS 13 160 4

PFBS 1,900 25,000 601 

PFHxS 130 1,600 39

PFNA 19 250 6 

Notes:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Army Aviation Support Facility #3, Mobile, Alabama

AECOM 6-2

6.2 Soil Physicochemical Analyses

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

size, which are important for evaluating transport through the soil medium. Appendix F contains 

the results of the TOC, pH, and grain size sampling. 

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

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

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

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

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

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

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

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

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

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

6.3 AOI 1

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

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

6-5. Soil and groundwater results are presented on Figure 6-1 through Figure 6-7.

6.3.1 AOI 1 Soil Analytical Results

Surface soil was sampled from 0 to 2 feet bgs at boring locations AOI01-01 through AOI01-03

and MOB-01 through MOB-03. Soil was also sampled from shallow subsurface soil (10 to 15 feet 

bgs) and deep subsurface soil (22 to 32 feet bgs) at boring locations AOI01-01 through AOI01-03 

and MOB-01. AOI01-01 and MOB-02 were located to the north-northwest of the Flight Ramp;

MOB-01 was located to the east-northeast of the Flight Ramp; AOI01-02 and MOB-03 were 

located to the west-southwest of the Flight Ramp; and AOI01-03 was located to the south of the 

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

through Table 6-4 summarize the soil results.

PFOA, PFOS, PFHxS, and PFNA were detected in surface soil at concentrations below their SLs. 

PFOS and PFHxS were also detected in deep subsurface soil. There were no detections of PFOA, 

PFOS, PFHxS, or PFNA in shallow subsurface soil. PFBS was not detected in soil at any interval.

In surface soil, PFOA, PFOS, PFHxS, and PFNA were detected at least two orders of magnitude 

below their SLs. The maximum detected concentration among all four compounds was PFOA, 

which was detected at 0.547 J micrograms per kilogram (μg/kg) at MOB-02. PFBS was not 

detected.

In the shallow subsurface soil, PFOA, PFOS, PFBS, PFHxS, and PFNA were not detected. In the 

deep subsurface soil, PFOA, PFBS, and PFNA were not detected. PFOS and PFHxS were 

detected in deep subsurface soil at MOB-01, at concentrations below 1 μg/kg.

6.3.2 AOI 1 Groundwater Analytical Results

Groundwater was sampled from temporary monitoring wells AOI01-01 through AOI01-03 and 

MOB-01. Figure 6-6 and Figure 6-7 present the ranges of detections in groundwater. Table 6-5 

summarizes the groundwater results. 
Site Inspection Report

Army Aviation Support Facility #3, Mobile, Alabama

AECOM 6-3

PFOS was detected in groundwater at concentrations above the SL. PFOA, PFBS, and PFHxS 

were detected in groundwater, at concentrations below their SLs. PFNA was not detected in 

groundwater.

PFOS exceeded the 4 nanograms per liter (ng/L) groundwater SL at all AOI 1 temporary wells,

except AOI01-02, and was detected at a maximum concentration of 12.6 ng/L in MOB-01. The 

maximum observed concentrations of PFOA, PFBS, and PFHxS were also detected at MOB-01, 

but were below their SLs, at concentrations of 2.09 J ng/L, 1.08 J ng/L, and 4.32 J ng/L, 

respectively.

6.3.3 AOI 1 Conclusions

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

concentrations below their SLs. PFOS was detected in groundwater at several locations, at 

concentrations above the SL. PFOA, PFBS, and PFHxS were detected in groundwater, at 

concentrations below their SLs. Based on the exceedances of the PFOS SL 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: Hangar Fire Suppression System, Wash Rack, and AFFF Storage Area. The results in soil 

and groundwater are summarized on Table 6-2 through Table 6-5. Soil and groundwater results 

are presented on Figure 6-1 through Figure 6-7.

6.4.1 AOI 2 Soil Analytical Results

Surface soil was sampled from 0 to 2 feet bgs at boring locations AOI02-01 through AOI02-04. 

Soil was also sampled from shallow subsurface soil (13 to 15 feet bgs) and deep subsurface soil 

(33 to 35 feet bgs) at boring locations AOI02-01 through AOI02-03. AOI02-01 was located to the 

north of the Hangar; AOI02-02 was located to the east of the Hangar and north of the Wash Rack;

AOI02-03 was located to the west of the AFFF Storage Area; and AOI02-04 was located to the 

east of the Wash Rack. Figure 6-1 through Figure 6-5 present the ranges of detections in soil. 

Table 6-2 through Table 6-4 summarize the soil results.

PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in surface soil, at concentrations below 

their SLs. PFOS was also detected in deep subsurface soil. There were no detections of PFOA, 

PFOS, PFBS, PFHxS, or PFNA in shallow subsurface soil.

In surface soil, PFOA, PFOS, PFBS, PFHxS, and PFNA were detected at least one order of 

magnitude below their SLs. The maximum detected concentration among all five compounds was 

PFOS, which was detected at 1.74 μg/kg at A0I02-04.

In the shallow subsurface soil, PFOA, PFOS, PFBS, PFHxS, and PFNA were not detected. In the 

deep subsurface soil, PFOA, PFBS, PFHxS, and PFNA were not detected. PFOS was detected 

in deep subsurface soil only at AOI02-03, at a concentration of 0.068 J μg/kg.

6.4.2 AOI 2 Groundwater Analytical Results

Groundwater was sampled from temporary monitoring wells AOI02-01 through AOI02-03. Figure 

6-6 and Figure 6-7 present the ranges of detections in groundwater. Table 6-5 summarizes the 

groundwater results.
Site Inspection Report

Army Aviation Support Facility #3, Mobile, Alabama

AECOM 6-4

PFOA was detected in groundwater, at a concentration above the SL. PFOS, PFBS, and PFHxS 

were detected in groundwater, at concentrations below their SLs. PFNA was not detected in 

groundwater.

PFOA exceeded the 6 ng/L groundwater SL at one location, AOI02-02, at a concentration of 6.96 

ng/L. The maximum observed concentrations of PFOS, PFBS, and PFHxS were also detected at

AOI02-02, but below their SLs, at concentrations of 2.20 J ng/L, 3.50 J ng/L, and 16.0 ng/L, 

respectively.

6.4.3 AOI 2 Conclusions

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

concentrations below their SLs. PFOA was detected in groundwater, at a concentration above the

SL. PFOS, PFBS, and PFHxS were detected in groundwater, at concentrations below their SLs. 

Based on the exceedance of the PFOA SL in groundwater, further evaluation at AOI 2 is 

warranted. 
Table 6-2

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

Site Inspection Report, AASF #3 Bates Field

Analyte OSD Screening 

Level a

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

PFBS 1900 ND U ND U ND U ND U ND U ND U ND U ND U ND U ND U

PFHxS 130 ND U ND U ND U ND U ND U 0.057 J ND U ND U ND U ND U

PFNA 19 0.075 J 0.075 J 0.021 J 0.035 J 0.039 J 0.239 J 0.033 J ND UJ 0.027 J 0.026 J

PFOA 19 0.171 J 0.153 J ND U 0.143 J ND U 0.547 J ND U ND U 0.083 J ND U

PFOS 13 0.184 J 0.189 J ND U 0.076 J 0.169 J 0.221 J 0.123 J 0.062 J 0.106 J ND U

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AASF Army Aviation Support Facility

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

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

DL detection limit

Notes ft feet

ND = Analyte not detected above the LOD. LOD values are presented in Appendix F. HQ hazard quotient

ID identification

LCMSMS liquid chromatography with tandem mass spectrometry

LOD limit of detection

MOB Mobile

ND analyte not detected above the LOD

OSD Office of the Secretary of Defense

QSM Quality Systems Manual

Qual interpreted qualifier

SB soil boring

USEPA United States Environmental Protection Agency

μg/kg micrograms per kilogram

Area of Interest

Sample ID

Sample Date

Depth

AOI01-01-SB-00-02

01/22/2022

0-2 ft

AOI01-01-SB-00-02-D

01/22/2022

0-2 ft

AOI01-02-SB-00-02

01/23/2022

0-2 ft

MOB-03-SB-00-02

01/23/2022

0-2 ft

AOI01-03-SB-00-02

01/23/2022

0-2 ft

MOB-01-SB-00-02

01/22/2022

0-2 ft

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

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

AOI01 AOI02

AOI02-02-SB-00-02

01/24/2022

0-2 ft

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

MOB-03-SB-00-02-D

01/23/2022

0-2 ft

AOI02-01-SB-00-02

01/24/2022

0-2 ft

MOB-02-SB-00-02

01/22/2022

0-2 ft

AECOM 6-5
Table 6-2

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

Site Inspection Report, AASF #3 Bates Field

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual

PFBS 1900 ND U 0.039 J ND U

PFHxS 130 ND U 0.157 J 0.045 J

PFNA 19 0.027 J 0.039 J 0.031 J

PFOA 19 ND U ND U ND U

PFOS 13 ND U 0.725 J 1.74

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AASF Army Aviation Support Facility

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

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

DL detection limit

Notes ft feet

ND = Analyte not detected above the LOD. LOD values are presented in Appendix F. HQ hazard quotient

ID identification

LCMSMS liquid chromatography with tandem mass spectrometry

LOD limit of detection

MOB Mobile

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

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

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

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

AOI02

AOI02-03-SB-00-02

01/23/2022

0-2 ft

AOI02-04-SB-00-02

01/23/2022

0-2 ft

Area of Interest

Sample ID

Sample Date

Depth

AOI02-02-SB-00-02-D

01/24/2022

0-2 ft

AECOM 6-6
Table 6-3

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

Site Inspection Report, AASF #3 Bates Field

Analyte OSD Screening 

Level a

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

PFBS 25000 ND U ND U ND U ND U ND U ND U ND U

PFHxS 1600 ND U ND U ND U ND U ND U ND U ND U

PFNA 250 ND U ND U ND U ND U ND U ND U ND U

PFOA 250 ND U ND U ND U ND U ND U ND U ND U

PFOS 160 ND U ND U ND U ND U ND U ND U ND U

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

U = The analyte was not detected at a level greater than or equal to the adjusted DL AASF Army Aviation Support Facility

AOI Area of Interest

Notes D duplicate

ND = Analyte not detected above the LOD. LOD values are presented in Appendix F. DL detection limit

ft feet

HQ hazard quotient

ID identification

LCMSMS liquid chromatography with tandem mass spectrometry

LOD limit of detection

MOB Mobile

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

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

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

USEPA’s Regional Screening Level Calculator. HQ=0.1, May 2022. Soil screening levels based on industrial/commercial composite worker scenario for incidental

ingestion of contaminated soil.

AOI02

AOI02-03-SB-13-15

01/23/2022

13-15 ft

MOB-01-SB-13-15

01/22/2022

13-15 ft

AOI02-01-SB-13-15

01/24/2022

13-15 ft

AOI02-02-SB-13-15

01/24/2022

13-15 ft

AOI01-02-SB-13-15

Area of Interest

Sample ID

Sample Date

Depth

AOI01-01-SB-10-12

01/23/2022

10-12 ft

AOI01

01/23/2022

13-15 ft

AOI01-03-SB-13-15

01/23/2022

13-15 ft

AECOM 6-7
Table 6-4

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

Site Inspection Report, AASF #3 Bates Field

Area of Interest

Sample ID

Sample Date

Depth

Analyte Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual

PFBS ND U ND U ND U ND U ND U ND U ND U

PFHxS ND U ND U ND U 0.138 J ND U ND U ND U

PFNA ND U ND U ND U ND U ND U ND U ND U

PFOA ND U ND U ND U ND U ND U ND U ND U

PFOS ND U ND U ND U 0.951 J ND U ND U 0.068 J

Interpreted Qualifiers Chemical Abbreviations

J = Estimated concentration PFBS perfluorobutanesulfonic acid

U = The analyte was not detected at a level greater than or equal to the adjusted DL PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

Notes PFOA perfluorooctanoic acid

ND = Analyte not detected above the LOD. LOD values are presented in Appendix F. PFOS perfluorooctanesulfonic acid

Acronyms and Abbreviations

AASF Army Aviation Support Facility

AOI Area of Interest

D duplicate

DL detection limit

ft feet

ID identification

LCMSMS liquid chromatography with tandem mass spectrometry

LOD limit of detection

MOB Mobile

ND analyte not detected above the LOD

QSM Quality Systems Manual

Qual interpreted qualifier

SB soil boring

μg/kg micrograms per kilogram

28-30 ft

AOI01

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

AOI02-01-SB-33-35

01/24/2022

33-35 ft

AOI01-01-SB-22-24

01/23/2022

22-24 ft

AOI01-02-SB-30-32

01/24/2022

30-32 ft

MOB-01-SB-28-30

01/22/2022

AOI01-03-SB-30-32

01/23/2022

30-32 ft

AOI02

AOI02-02-SB-33-35 AOI02-03-SB-33-35

01/24/2022

33-35 ft

01/24/2022

33-35 ft

AECOM 6-8
Table 6-5

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

Site Inspection Report, AASF #3 Bates Field

Analyte OSD Screening 

Level a

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

PFBS 601 ND U ND U ND U ND U 1.08 J ND U 3.50 J ND U

PFHxS 39 ND UJ 1.34 J ND U ND U 4.32 J ND U 16.0 ND U

PFNA 6 ND U ND U ND U ND U ND U ND U ND U ND U

PFOA 6 ND U ND U ND U 0.969 J 2.09 J ND U 6.96 ND U

PFOS 4 6.71 7.66 2.08 J 5.31 12.6 1.97 J 2.20 J 1.11 J

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AASF Army Aviation Support Facility

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

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

DL detection limit

Notes GW groundwater

ND = Analyte not detected above the LOD. LOD values are presented in Appendix F. HQ hazard quotient

ID identification

LCMSMS liquid chromatography with tandem mass spectrometry

LOD limit of detection

MOB Mobile

ND analyte not detected above the LOD

OSD Office of the Secretary of Defense

QSM Quality Systems Manual

Qual interpreted qualifier

USEPA United States Environmental Protection Agency

ng/l nanogram per liter

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

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

USEPA’s Regional Screening Level Calculator. HQ=0.1, May 2022 Groundwater screening levels based on residential scenario for direct ingestion of groundwater.

AOI02

AOI02-02-GW

01/24/2022

AOI02-03-GW

01/25/2022

AOI01-03-GW

01/24/2022

AOI02-01-GW

01/25/2022

AOI01-01-GW-D

01/23/2022

AOI01-02-GW

01/25/2022

Area of Interest

Sample ID

Sample Date

AOI01-01-GW

01/23/2022

AOI01

MOB-01-GW

01/23/2022

AECOM 6-9
THIS PAGE INTENTIONALLY BLANK

COM 6-10
AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

AOI02-04

MOB-01

MOB-02

MOB-03

AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

MOB-01 AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

MOB-01

­ Figure 6-1

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Bates Field AASF #3, AL

9/1/2022

9/1/2022

9/1/2022

MS

VG

CM

GIS BY

CHK BY

PM

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

9/1/2022

1:4,208

Legend

Facility Boundary

PFOA Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

0 175 350 700

Feet

Shallow Intermediate Deep

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

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

PFOA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

AECOM 6-11
AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

AOI02-04

MOB-01

MOB-02

MOB-03

AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

MOB-01 AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

MOB-01

­ Figure 6-2

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Bates Field AASF #3, AL

8/12/2022

8/12/2022

8/12/2022

MS

VG

CM

GIS BY

CHK BY

PM

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

8/12/2022

1:4,208

Legend

Facility Boundary

PFOS Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

0 175 350 700

Feet

Shallow Intermediate Deep

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

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

PFOS Results (μg/Kg)

ND

>ND - 13

>13 - 160

>160 - 1,600

>1,600

AECOM 6-12
AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

AOI02-04

MOB-01

MOB-02

MOB-03

AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

MOB-01 AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

MOB-01

­ Figure 6-3

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Bates Field AASF #3, AL

8/12/2022

8/12/2022

8/12/2022

MS

VG

CM

GIS BY

CHK BY

PM

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

8/12/2022

1:4,208

Legend

Facility Boundary

PFBS Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

0 175 350 700

Feet

Shallow Intermediate Deep

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

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

PFBS Results (μg/Kg)

ND

>ND - 10

>10 - 1,900

>1,900 - 25,000

>25,000

AECOM 6-13
AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

AOI02-04

MOB-01

MOB-02

MOB-03

AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

MOB-01 AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

MOB-01

­ Figure 6-4

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Bates Field AASF #3, AL

8/12/2022

8/12/2022

8/12/2022

MS

VG

CM

GIS BY

CHK BY

PM

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

8/12/2022

1:4,208

Legend

Facility Boundary

PFHxS Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

0 175 350 700

Feet

Shallow Intermediate Deep

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

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

PFHxS Results (μg/Kg)

ND

>ND - 10

>10 - 130

>130 - 1,600

>1,600

AECOM 6-14
AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

AOI02-04

MOB-01

MOB-02

MOB-03

AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

MOB-01 AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

MOB-01

­ Figure 6-5

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Bates Field AASF #3, AL

8/12/2022

8/12/2022

8/12/2022

MS

VG

CM

GIS BY

CHK BY

PM

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

8/12/2022

1:4,208

Legend

Facility Boundary

PFNA Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

0 175 350 700

Feet

Shallow Intermediate Deep

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

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

PFNA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

AECOM 6-15
AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

MOB-01

PFOA Results (ng/L)

ND

>ND - 6

>6 - 40

>40 - 70

>70

AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

MOB-01 AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

MOB-01

­ Figure 6-6

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Bates Field AASF #3, AL

10/5/2022

10/5/2022

10/5/2022

MS

VG

CM

GIS BY

CHK BY

PM

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

10/5/2022

1:4,208

Legend

Facility Boundary

Groundwater Flow Direction

PFOA, PFOS, and PFBS Detections in Groundwater

12420 Milestone Center Drive

Germantown, MD 20876

0 175 350 700

Feet

PFOA PFOS PFBS

PFBS Results (ng/L)

ND

>ND - 100

>100 - 601

>601 - 2,000

>2,000

PFOS Results (ng/L)

ND

>ND - 4

>4 - 40

>40 - 70

>70

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

AECOM 6-16
AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

MOB-01

PFHxS Results (ng/L)

ND

>ND - 39

>39 - 100

>100 - 1,000

>1,000

AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI02-03

MOB-01

­ Figure 6-7

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Bates Field AASF #3, AL

9/1/2022

9/1/2022

9/1/2022

MS

VG

CM

GIS BY

CHK BY

PM

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

9/1/2022

1:4,196

Legend

Facility Boundary

Groundwater Flow Direction

PFHxS and PFNA Detections in Groundwater

12420 Milestone Center Drive

Germantown, MD 20876

0 175 350 700

Feet

PFHxS PFNA

PFNA Results (ng/L)

ND

>ND - 6

>6 - 100

>100 - 1,000

>1,000

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

AECOM 6-17
THIS PAGE INTENTIONALLY BLANK

6-18
Site Inspection Report

Army Aviation Support Facility #3, Mobile, Alabama

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 7-2. Please note that while the CSM discussion assists in determining if a receptor may 

be impacted, the decision to move from SI to Remedial Investigation (RI) or interim action is 

determined based upon exceedances of the SLs for the relevant compounds and whether the 

release is more than likely attributable to the DoD. A CSM presents the current understanding of 

the site conditions with respect to known and suspected sources, potential transport mechanisms 

and migration pathways, and potentially exposed human receptors. A human exposure pathway 

is considered potentially complete when the following conditions are present:

1. Contaminant source;

2. Environmental fate and transport;

3. Exposure point;

4. Exposure route; and

5. Potentially exposed populations.

If any of these elements are missing, the pathway is incomplete. The CSM 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 the 

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

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

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

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

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

the CSMs indicate whether potentially complete exposure pathways may exist, the 

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

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

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

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

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

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

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

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

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

boundary, and recreational users outside of the facility boundary.

7.1 Soil Exposure Pathway

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

between the source and potential receptors at AOI 1 and AOI 2 based on the aforementioned 

criteria.

7.1.1 AOI 1

AOI 1 contains one potential release area. According to ALARNG personnel with knowledge of 

the facility dating back to 2002, approximately 10 AFFF Tri-MaxTM 30 mobile extinguisher units 

were staged along the Flight Ramp southwest of the hangar building. The Tri-MaxTM 30 units were 

maintained by a contractor. Prior to removal of the Tri-MaxTM 30 units around 2008, some of the 
Site Inspection Report

Army Aviation Support Facility #3, Mobile, Alabama

AECOM 7-2

units were discharged on the southeast portion of the Flight Ramp. Grassy areas are adjacent to 

the Flight Ramp.

PFOA, PFOS, PFHxS, and PFNA were detected in surface soil, at concentrations below their 

SLs. Site workers and future construction workers could contact constituents in surface soil via 

incidental ingestion and inhalation of dust. Therefore, the soil exposure pathways for those 

receptors are considered potentially complete. Additionally, off-facility residential and recreational 

users across Tanner Williams Road to the northeast may be potentially exposed to constituents 

in surface soil via inhalation of dust. The surface soil exposure pathway for trespassers is 

incomplete because the facility has secure access. In the shallow subsurface soil, PFOA, PFOS, 

PFBS, PFHxS, and PFNA were not detected. PFOS and PFHxS were detected at trace 

concentrations in the deep subsurface soil; however, the construction worker exposure scenario 

assumes excavation occurs at depths at or above 15 feet bgs. Therefore, the soil exposure 

pathway for incidental ingestion of subsurface soil by construction workers is considered 

incomplete. The CSM for AOI 1 is presented on Figure 7-1. 

7.1.2 AOI 2

AOI 2 contains three potential release areas. Since 1999, the AASF #3 hangar has used an 

overhead fire suppression system. The current overhead fire suppression system is equipped 

with an 800-gallon AFFF tank filled with Chemguard 3% AFFF. Two poly 55-gallon drums 

containing Chemguard 3% are stored in the chemical storage building. Annual fire training using 

Purple K units was reportedly conducted at the Wash Rack. The Wash Rack and all hangar drains 

convey to the OWS, which then drains to the sanitary sewer, or to the overflow basin in upset 

conditions and on to the retention pond. Grassy areas are adjacent to AOI 2.

PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in surface soil, at concentrations below 

their SLs. Site workers and future construction workers could contact constituents in surface soil 

via incidental ingestion and inhalation of dust. Therefore, the soil exposure pathways for those 

receptors are considered potentially complete. Additionally, off-facility residential and recreational 

users across Tanner Williams Road to the northeast may be potentially exposed to constituents 

in surface soil via inhalation of dust. The surface soil exposure pathway for trespassers is 

incomplete because the facility has secure access. In the shallow subsurface soil, PFOA, PFOS, 

PFBS, PFHxS, and PFNA were not detected. PFOS was detected at trace concentrations in the 

deep subsurface soil; however, the construction worker exposure scenario assumes excavation 

occurs at depths at or above 15 feet bgs. Therefore, the soil exposure pathway for incidental 

ingestion of subsurface soil by construction workers is considered incomplete. The CSM for AOI 

2 is presented on Figure 7-2. 

7.2 Groundwater Exposure Pathway

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

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

7.2.1 AOI 1

PFOS was detected in groundwater, at concentrations above the SL. Drinking water at AASF #3

is provided by MAWSS, which sources all drinking water from Big Creek Lake, located 

approximately 3 miles northwest of the facility. Therefore, the ingestion exposure pathway for site 

workers and the groundwater exposure pathway for trespassers are incomplete due to secure 

facility access. Multiple domestic wells that could potentially be in use were identified within 1 mile 

of the facility. These wells are in the up- and side-gradient directions relative to inferred regional 

groundwater flow; however, the variability in groundwater flow observed at the facility may place

some of these wells downgradient. Therefore, the ingestion pathway for off-facility residents is 
Site Inspection Report

Army Aviation Support Facility #3, Mobile, Alabama

AECOM 7-3

conservatively considered potentially complete. At AOI 1, groundwater was observed at depths 

ranging between 22.68 to 33.23 feet bgs. The construction worker exposure scenario assumes 

excavation occurs at depths at or above 15 feet bgs. Therefore, the incidental ingestion exposure 

pathway is considered incomplete for future construction workers. The CSM for AOI 1 is presented 

on Figure 7-1.

7.2.2 AOI 2

PFOA was detected in groundwater, at concentrations above the SL. Drinking water at AASF #3

is provided by MAWSS, which sources all drinking water from Big Creek Lake, located 

approximately 3 miles northwest of the facility. Therefore, the ingestion exposure pathway to site 

workers is considered incomplete. Multiple domestic wells that could potentially still be in use 

were identified within 1 mile of the facility. These wells are in the up- and side-gradient directions 

relative to inferred regional groundwater flow; however, the variability in groundwater flow 

observed at the facility may place some of these wells downgradient. Therefore, the ingestion 

pathway for off-facility residents is considered potentially complete. At AOI 2, groundwater was 

observed at depths ranging between 33.88 to 34.63 feet bgs. Therefore, the incidental 

groundwater exposure pathway is considered incomplete for future construction workers. The 

CSM for AOI 2 is presented on Figure 7-2.

7.3 Surface Water and Sediment Exposure Pathway

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

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

between the source and potential receptors. PFAS are water soluble and can migrate readily from 

soil to surface water via leaching and run-off. Surface water drainage from the Flight Ramp

appears to flow northwest via sheet flow or via shallow drainage on the west side of the ramp to 

the retention pond located at the northwest corner of the facility property. The retention pond has 

no outflow and empties through infiltration or evaporation. Surface water in the vicinity of AASF 

#3 that is not captured by the retention pond drains to the northwest, towards Pierce Creek, 

located 0.5 miles northwest of the facility. Pierce Creek flows southwest and drains into Big Creek 

downstream of Big Creek Lake, which is the main source of drinking water for almost 70% of 

Mobile County (MAWSS, 2019). Big Creek continues to flow southwest into Mississippi, where it 

empties into the Escatawpa River.

7.3.1 AOI 1

At AOI 1, PFOA, PFOS, PFHxS, and PFNA were detected in soil. Runoff from the Flight Ramp 

drains primarily to the on-facility retention pond. It is also possible that constituents released to 

the ground surface and not captured by the pond may have migrated off-facility to Pierce Creek.

Therefore, site workers, future construction workers, and off-facility recreational users may be 

exposed to these constituents in surface water and sediment via the incidental ingestion exposure 

pathway. The surface water and sediment exposure pathway is incomplete for trespassers due to 

the secure facility access. PFOA, PFOS, PFBS, and PFHxS were detected in groundwater; 

however, groundwater to surface water discharge is not anticipated based on site conditions. The 

CSM for AOI 1 is presented on Figure 7-1.

7.3.2 AOI 2

At AOI 2, PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in soil. Drainage from the 

Hangar and Wash Rack during upset conditions flows to the retention pond. It is also possible 

that those constituents released to the ground surface and not captured by the pond may have 

migrated from off-facility to Pierce Creek. Therefore, site workers, future construction workers, 
Site Inspection Report

Army Aviation Support Facility #3, Mobile, Alabama

AECOM 7-4

and off-facility recreational users may be exposed to these constituents in surface water and 

sediment via the incidental ingestion exposure pathway. PFOA, PFOS, PFBS, and PFHxS were 

detected in groundwater; however, groundwater to surface water discharge is not anticipated 

based on facility conditions. The CSM for AOI 2 is presented on Figure 7-2. 
Media

SOURCE PATHWAY R

AOI 1

Historical 

Mobile Fire 

Extinguisher 

Staging and 

Discharge on 

Flight Ramp

Subsurface 

Soil

Human 

Activities

Precipitation/ 

Run-Off

Leaching/ Infiltration

Airborne Soil 

particulate

Surface Soil 

Surface 

Water/ 

sediment

Subsurface 

Soil

Shallow 

Groundwater

Source Release Mechanism Media Transport and Migration Media Exposure Routes

Inhalation of 

Dust

IngestionIngestion

Ingestion

Ingestion

Hu

C

Flow-Chart ContinuesPartial / Possible FlowFlow-Chart StopsIncomplete PathwayPotentially Complete PathwayPotentially Complete Pathway with Exceedance of SL

/ 

LEGEND

Figure 7

Conceptual Site M

AASF #3, Mobile

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

Surface 

Water

Surface 

Water Flow

NOTES1. The resident and recreational usersrefer to off-site receptors.2. No active construction was observedat the AOI during the SI field event.

Surface Soil

Site 

Worker

Con

W

/ 

/ 

Site 

Worker

Con

W

/ 

/ 

AECOM 
Media

SOURCE PATHWAY R

AOI 2

AFFF Fire 

Suppression 

System, 

Annual Fire 

Training 

Activities, and 

AFFF Storage

Surface Soil

Subsurface 

Soil

Human 

Activities

Precipitation/ 

Run-Off

Leaching/ Infiltration

Airborne Soil 

particulate

Surface Soil 

Surface 

Water/ 

sediment

Subsurface 

Soil

Shallow 

Groundwater

Source Release Mechanism Media Transport and Migration Media Exposure Routes

Inhalation of 

Dust

IngestionIngestion

Ingestion

Ingestion

Hu

C

Flow-Chart ContinuesPartial / Possible FlowFlow-Chart StopsIncomplete PathwayPotentially Complete PathwayPotentially Complete Pathway with Exceedance of SL

LEGEND

Figure 7

Conceptual Site M

AASF #3, Mobile

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

Surface 

Water

Surface 

Water Flow

NOTES1. The resident and recreational usersrefer to off-site receptors.2. No active construction was observedat the AOI during the SI field event.

Site 

Worker

Con

W

Site 

Worker

Con

W

/ / 

/ 

/ 

/ 

AECOM 
Site Inspection Report

Army Aviation Support Facility #3, Mobile, Alabama

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 18 to 25 January 2022 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, 2021).

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

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

Table B-15 as follows. 

• Twenty-four (24) soil samples from ten (10) locations; 

• Seven (7) grab groundwater samples from seven (7) temporary wells; and

• Sixteen (16) QA/QC samples.

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

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

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

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

required. Additionally, the CSMs were refined to assess whether a potentially complete pathway 

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

described in Section 7.

8.2 Outcome 

Based on the results of this SI, further evaluation is warranted in an RI for AOI 1: Flight Ramp and 

AOI 2: Hangar Fire Suppression System, Wash Rack, and AFFF Storage Area. Based on the 

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

water receptors from AOI 1 and AOI 2 from sources on the facility resulting from historical DoD 

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

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

relative to the SLs is as follows:

• At AOI 1:

• The detected concentrations of PFOA, PFOS, PFHxS, and PFNA in soil at AOI 1 

were below their SLs. PFBS was not detected in soil at AOI 1.

• PFOS in groundwater exceeded the SL of 4 ng/L at wells AOI01-01, AOI01-03, and 

MOB-01, at concentrations of 7.66 ng/L, 5.31 ng/L, and 12.6 ng/L, respectively. 

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

• At AOI 2:

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

AOI 1 were below their SLs. 
Site Inspection Report

Army Aviation Support Facility #3, Mobile, Alabama

AECOM 8-2

• PFOA in groundwater exceeded the SL of 6 ng/L at AOI02-02, at a concentration of 

6.96 ng/L. Based on the results of the SI, further evaluation of AOI 2 is warranted in 

an RI.

Groundwater elevations, calculated using depth to groundwater measurements and the surveyed 

ground surface elevation, were generally higher in the north-northwest investigation area and 

decreased towards the south-southeast, with the exception of elevated groundwater measured in 

the southern portion of the facility. As a result, the SI findings show an overall southeasterly 

groundwater flow direction on the facility. In the northern portion of the facility, groundwater may 

be artificially elevated by the retention pond, and in the southern portion of the facility, groundwater 

may be perched atop a clay layer. The natural groundwater flow direction in the vicinity of AASF 

#3 is not known, but it is inferred to be to the southwest.

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

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

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

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

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

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

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

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

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

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

AOI Potential 

Release Area

Soil –

Source 

Area

Groundwater – 

Source Area

Future 

Action

1 Flight Ramp Proceed to 

RI 

2

Hangar Fire 

Suppression 

System, Wash 

Rack, and AFFF 

Storage Area

Proceed to 

RI

Legend:

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected
Site Inspection Report

Army Aviation Support Facility #3, Mobile, Alabama

AECOM 9-1

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