FINAL

Site Inspection Report 

Lexington Army Aviation Support 

Facility #1

Lexington, Oklahoma

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 

May 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 Northern Release Areas ............................................................................... 3-1

3.1.1 Flight Line..................................................................................................... 3-1

3.1.2 Burn Pit......................................................................................................... 3-1

3.2 AOI 2 Eastern Release Areas................................................................................. 3-1

3.2.1 Hangar 2....................................................................................................... 3-2

3.2.2 Old Fire Station............................................................................................. 3-2

3.2.3 Old Wash Rack............................................................................................. 3-2

3.2.4 Grassy Area Behind Hangar 1...................................................................... 3-2

3.2.5 Storage Building ........................................................................................... 3-3

3.2.6 Old AFFF Storage Location .......................................................................... 3-3

3.2.7 Lagoons........................................................................................................ 3-3

3.3 AOI 3 Mobile Refueler Parking Area....................................................................... 3-3

3.4 AOI 4 Fuel Point ..................................................................................................... 3-3

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............................................................................... 5-3

5.3 Surface Water Sampling ......................................................................................... 5-4

5.4 Permanent Well Installation and Groundwater Sampling ....................................... 5-4

5.5 Synoptic Water Level Measurements ..................................................................... 5-5

5.6 Surveying................................................................................................................ 5-5
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5.7 Investigation-Derived Waste ................................................................................... 5-5

5.8 Laboratory Analytical Methods................................................................................ 5-6

5.9 Deviations from the SI QAPP Addendum ............................................................... 5-6

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

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 ......................................................... 6-4

6.4.3 AOI 2 Surface Water Analytical Results ....................................................... 6-4

6.4.4 AOI 2 Conclusions........................................................................................ 6-4

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

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

6.5.2 AOI 3 Conclusions........................................................................................ 6-5

6.6 AOI 4....................................................................................................................... 6-5

6.6.1 AOI 4 Soil Analytical Results ........................................................................ 6-5

6.6.2 AOI 4 Conclusions........................................................................................ 6-5

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

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

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

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

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

7.1.4 AOI 4 ............................................................................................................ 7-3

7.2 Groundwater Exposure Pathway ............................................................................ 7-3

7.2.1 AOI 1 ............................................................................................................ 7-3

7.2.2 AOI 2 ............................................................................................................ 7-4

7.2.3 AOI 3 ............................................................................................................ 7-4

7.2.4 AOI 4 ............................................................................................................ 7-4

7.3 Surface Water and Sediment Exposure Pathway................................................... 7-4

7.3.1 AOI 1 ............................................................................................................ 7-4

7.3.2 AOI 2 ............................................................................................................ 7-5

7.3.3 AOI 3 and AOI 4 ........................................................................................... 7-5

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

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

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

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

Appendix A Data Usability Assessment and Validation Reports

Appendix B Field Documentation

B1. Log of Daily Notice of Field Activities

B2. Sampling Forms

B3. Nonconformance and Corrective Action Reports

B4. Survey Data

Appendix C Photographic Log

Appendix D TPP Meeting Minutes

Appendix E Boring Logs and Well Construction Forms 

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, April 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 6-8 PFOA, PFOS, and PFBS Detections in Surface Water

Figure 6-9 PFHxS and PFNA Detections in Surface Water

Figure 7-1 Conceptual Site Model, AOI 1

Figure 7-2 Conceptual Site Model, AOI 2

Figure 7-3 Conceptual Site Model, AOI 3

Figure 7-4 Conceptual Site Model, AOI 4

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 and Permanent Well Screen Intervals

Table 5-3 Depths to Water and Groundwater Elevations in Permanent Wells

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 6-6 PFOA, PFOS, PFBS, PFNA, and PFHxS Results in Surface Water

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

amsl above mean sea level

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

DO dissolved oxygen

DOT Department of Transportation

DQO data quality objective

DUA data usability assessment

ELAP Environmental Laboratory Accreditation Program

EM Engineer Manual

FedEx Federal Express

GPRS Ground Penetrating Radar Systems

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

MIL-SPEC military specification

NELAP National Environmental Laboratory Accreditation Program

ng/L nanograms per liter

OKARNG Oklahoma Army National Guard

OKIE811 Oklahoma 811

ORP oxidation-reduction potential

OSD Office of the Secretary of Defense

PA Preliminary Assessment

PFAS per- and polyfluoroalkyl substances

PFBS perfluorobutanesulfonic acid

PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid
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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

RI Remedial Investigation

SI Site Inspection

SL screening level

sonic rotary sonic

SOP standard operating procedure

TOC total organic carbon

TPP Technical Project Planning

UFP Uniform Federal Policy

US United States

USACE United States Army Corps of Engineers

USCS Unified Soil Classification System

USEPA United States Environmental Protection Agency

USFWS United States Fish and Wildlife Service
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Executive Summary

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

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

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

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

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

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

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

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

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

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

used, stored, disposed, or released historically (see Table ES-2 for AOI 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 SLs for relevant 

compounds. This SI was completed at the Lexington Army Aviation Support Facility (AASF) #1 in 

Lexington, Oklahoma and determined further investigation is warranted for AOI 1: Northern 

Release Areas, AOI 2: Eastern Release Areas, and AOI 3: Mobile Refueler Parking Area. No 

further evaluation is warranted for AOI 4: Fuel Point at this time. Lexington AASF #1 will also be 

referred to as the “facility” throughout this document. 

Lexington AASF #1 is located at 16201 144 Avenue SE, approximately 30 miles southeast of 

Oklahoma City and 5 miles east of downtown Lexington, Cleveland County, Oklahoma. The

approximately 308-acre facility is situated at the junction of 144 Avenue SE and Oklahoma State 

Highway 39. Lexington AASF #1 was built in 1973 and acted as a naval base used for aerial 

gunnery; no naval flight operations took place at this time. In 1975, the ARNG took over the facility. 

The mission of the facility is to act as a maintenance facility for aviation units, to provide helicopter 

search and rescue, and assist in wildfire suppression. The facility includes two hangars, a fuel 

point, storage buildings, a maintenance shop (formally a fire station), administrative and ground 

support buildings, and parking areas (AECOM Technical Services, Inc., 2020).

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

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, AOI 2, and AOI 3.

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

Groundwater –

Facility 

Boundary

Future Action

1 Northern Release 

Areas N/A Proceed to RI 

2 Eastern Release 

Areas Proceed to RI

3 Mobile Refueler 

Parking Area N/A N/A Proceed to RI

4 Fuel Point N/A N/A No further action

Legend:

N/A = not applicable

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels
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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 Lexington Army 

Aviation Support Facility (AASF) #1 in Lexington, Oklahoma. Lexington AASF #1 is also referred 

to as the “facility” throughout this document. 

The SI project elements were performed in compliance with Comprehensive Environmental 

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

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

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

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

investigations. 

1.2 SI Purpose 

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

that identified four 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 

Lexington AASF #1 is located at 16201 144 Avenue SE, approximately 30 miles southeast of 

Oklahoma City and 5 miles east of downtown Lexington, Cleveland County, Oklahoma. The

approximately 308-acre facility is situated at the junction of 144 Avenue SE and Oklahoma State 

Highway 39 (Figure 2-1). Lexington AASF #1 was built in 1973 and acted as a naval base used 

for aerial gunnery; no naval flight operations took place at this time. In 1975, the ARNG took over 

the facility. 

The mission of Lexington AASF #1 is to act as a maintenance facility for aviation units, to provide 

helicopter search and rescue, and assist in wildfire suppression. The facility includes two hangars, 

a fuel point, storage buildings, a maintenance shop (formally a fire station), administrative and 

ground support buildings, and parking areas (AECOM, 2020). The central portion of the facility is 

developed with paved surfaces and buildings; grassy areas surround the buildings and airfield. 

The western portion of the facility is largely undeveloped fields and wooded land, and it is bisected 

by an unnamed tributary, a retention pond, and a section of Little Buckhead Creek. The eastern 

portion of the facility is also undeveloped and is bisected by an unnamed tributary. 

2.2 Facility Environmental Setting

Lexington AASF #1 is in the Central Redbed Plains physiographic region, which is characterized 

by red Permian sedimentary rocks, rolling hills, and flat plains (Tyrl et al., 2007). The topography 

at the facility slopes predominantly to the east and west, away from the airfield, which forms a 

topographic high centrally within the facility. Surface elevations range from approximately 1,060 

to 1,120 feet above mean sea level (amsl). The lowest elevations at the facility are located in the 

western portion, where Little Buckhead Creek crosses through the facility, and the highest 

elevations are located in the northeastern corner of the facility. Several unnamed tributaries to 

Buckhead Creek form lows adjacent to the airfield to the west and east and appear to be the 

primary on-facility drainages (Figure 2-2). 

The area surrounding Lexington AASF #1 is primarily open pasture and woodland. The Lexington 

Wildlife Management Area is located to the north of Lexington AASF #1, a livestock farm and 

residential property are located to the south, and the Oklahoma Department of Corrections

Lexington Correctional Center is located to the east. The Correctional Center and sparse 

residential properties occupy much of the developed land within a 1-mile radius of Lexington 

AASF #1. 

2.2.1 Geology

The geology at the facility consists of Quaternary alluvial deposits underlain by Permian and 

Pennsylvanian-aged units (Figure 2-3). The alluvium deposits in the region range from 0 to 100 

feet thick, have a wide compositional range, and consist of clay, silt, sand, and gravel (Chang and 

Stanley, 2010; Mashburn et al., 2019). The Permian-aged units, from youngest to oldest, consist 

of the Sumner, the Chase, the Council Grove, and the Admire Groups. The Pennsylvanian-aged 

Vanoss Formation underlies the Permian units (Chang and Stanley, 2010; Ellis et al., 2017; 

Mashburn et al., 2019). 

The Permian-aged units in central Oklahoma can generally be described as red to reddish-orange 

massive and cross-bedded, fine-grained sandstone interbedded with shale and siltstone (Ellis et 

al., 2017). The Sumner Group consists of the Garber Sandstone and the underlying Wellington 

Formation. These units are similar and can be difficult to differentiate; consequently, they are often 
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treated as one unit. The Garber Sandstone and Wellington Formation consist of cross-bedded, 

fine-grained sandstone with interbedded shale that range up to approximately 280 feet thick 

(Chang and Stanley, 2010; Mashburn et al., 2019). The Chase, Council Grove, and Admire groups 

are similar and are composed of cross-bedded, fine-grained sandstone, shale, and thin limestone. 

The Permian geologic units dip slightly to the west (Mashburn et al., 2019). The Vanoss Formation 

consists of reddish-brown to gray shale and thin limestone and sandstone beds (Chang and 

Stanley, 2010; Ellis et al., 2017; Mashburn et al., 2019).

During the SI, soil borings were completed to depths ranging between 20 to 65 feet below ground 

surface (bgs). Soils observed generally consisted of red to reddish brown silty sand and low 

plasticity fines (clay and silt), as well as minor concentrations of gravel. Approximately 0.5- to 2-

foot interbedded deposits of caliche, a hard calcified soil often associated with arid environments, 

were observed in four of the five borings. Bedrock was not encountered in the soil borings 

completed to depths up to 65 feet bgs during the SI; however, remnant structures indicative of 

highly weathered rock (blocky textures, laminated bedding, and fissures) were observed in 

several borings and are likely indicative of the Garber Formation, which is mapped as the primary 

surficial unit in the region. The silt, clay, sands, and minor amount of gravel observed during the 

SI are also consistent with Quaternary alluvial deposits that consist of, and were deposited atop 

of, the heavily weathered Garber. Differentiating between the weathered Garber Formation and 

alluvial deposits is difficult due to the degree of bedrock weathering and shared origin of the 

alluvium. Topographic position is likely the distinguishing factor, with alluvium being present along 

the slopes and bottoms of drainages and more intact material forming the topographic highs. 

Boring logs are presented in Appendix E. 

One sample for grain size analysis was collected at location LEX-MW002 (11 to 12 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 (50.03 percent [%]) and clay (36.52%), 

with minor amounts of sand (13.37%) and gravel (0.09%). Grain size results are presented in 

Appendix F. 

2.2.2 Hydrogeology

The hydrogeology at the facility consists of one underlying aquifer, the Central Oklahoma aquifer. 

The Canadian River alluvial aquifer is present less than 5 miles to the west of the facility but 

terminates due to the disappearance of the confining Hennessey Group (Mashburn et al., 2019).

The Central Oklahoma aquifer comprises multiple geologic groups, including (from youngest to 

oldest): Quaternary-aged deposits and the Sumner, Chase, Council Grove, and Admire Groups 

(Ellis et al., 2017; Mashburn et al., 2019). Within Cleveland County, the freshwater sourced from 

the Central Oklahoma aquifer is found in the Sumner Group, although saline water is present in 

the underlying units (Mashburn et al., 2019). The Vanoss Formation acts as a lower confining unit 

for the aquifer. The groundwater surface elevation of the Central Oklahoma aquifer near the facility 

is estimated to be approximately 1,050 feet amsl. Groundwater features in the 4-mile radius 

surrounding the facility are shown in Figure 2-3. 

Numerous local groundwater wells within approximately 2 miles of the facility were identified using 

the database maintained by the Oklahoma Water Resources Board. Over 100 wells were reported 

as domestic use, 9 were reported as agricultural/irrigation use, and 12 were reported as public 

water supply use. Domestic wells within the inferred and measured downgradient of the facility 

have total depths between 65 to over 300 feet bgs. Agricultural/irrigation wells within the inferred 

and measured downgradient of the facility have reported well depths between 160 to 220 feet bgs

(Oklahoma Water Resources Board, 2021). 

The drinking water at the facility comes from four supply wells near the Oklahoma Department of 

Corrections, the closest of which is less than 800 feet east-southeast and side-gradient from the 
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facility. The total depths of the public supply wells were all over 400 feet bgs. Downgradient public 

supply wells within a 2-mile radius were not identified (Oklahoma Water Resources Board, 2021). 

Groundwater in the vicinity of Lexington AASF #1 was anticipated to be encountered at depths of 

approximately 30 to 60 feet bgs. Synoptic groundwater level measurements collected during the 

SI were found to range between 12.75 to 51.08 feet bgs. The shallowest depths to groundwater 

were observed at AOI 2, in the vicinity of the Lagoons. These locations were topographically the 

lowest and were located near the tributary drainage on the east side of the facility; however, it is 

also possible that groundwater could be artificially elevated near the Lagoons. Groundwater 

elevations, calculated using depth to groundwater measurements and the surveyed ground 

surface elevation, were generally higher in the east-northeast investigation area and decreased 

towards the southwest. As a result, the SI findings show an overall southwest groundwater flow 

direction (Figure 2-4). 

2.2.3 Hydrology

Surface water in the vicinity of the facility consists of small creeks, ponds, and constructed

lagoons. The eastern half of AASF #1 drains into small ponds and an unnamed tributary of 

Buckhead Creek that appears to be intermittent throughout the year, noted to flow primarily during 

heavy rain events, but had water during the SI. Retention ponds and sanitary lagoons operated 

by the corrections facility are also found southeast of AASF #1, on the corrections facility property. 

The western side of AASF #1 includes two parallel, southwestern-flowing creeks that are 

tributaries of Buckhead Creek. The creek furthest to the east would receive most runoff from the 

western portion of AASF #1 and is unnamed, while the other is Little Buckhead Creek. These 

tributaries flow from the facility, into Buckhead Creek, and then southeast into the Canadian River. 

The Canadian River is approximately 5 miles south of the facility and has an easterly flow direction 

from the Buckhead Creek outfall. The Canadian River is used for fishing and small size boating 

(Natural Atlas, 2022), and residences sparsely border both the Buckhead Creek and Canadian 

River.

Constructed drainage ditches/pathways are present at the facility, especially on the western side 

of the AASF, and direct surface flow out to a centralized point on the western boundary of the 

facility, near the unnamed tributary. Surface water features at the facility are presented in Figure 

2-5. 

2.2.4 Climate 

Climate in eastern Oklahoma is classified as humid subtropical (Oklahoma Climatological Survey, 

2011). The average temperature of the City of Purcell, located west of the facility, is 60.05 degrees 

Fahrenheit (°F). Seasonally, temperatures vary from a summer average monthly high of 94 °F to 

a winter average monthly low of 23 °F. Average precipitation in Purcell is 41.6 inches (World 

Climate, 2022). 

2.2.5 Current and Future Land Use

Lexington AASF #1 encompasses approximately 308 acres of land and is located 5 miles east of 

Lexington, Oklahoma. The facility is bounded to the north by Lexington Wildlife Management 

Area, to the east by the Lexington Correctional Center, to the west by Little Buckhead Creek and 

Buckhead Creek, and to the south by a livestock farm and residential property. Oklahoma State 

Highway 39 crosses east to west about 0.5-miles south of the operational part of the facility. 

Lexington AASF #1 is a controlled access facility and currently includes two hangars, a fuel point, 

storage buildings, a maintenance shop (formally a fire station), administrative and ground support 

buildings, and parking areas. Reasonably anticipated future land use is not expected to change 

from the current land use. 
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 2-4

2.2.6 Sensitive Habitat and Threatened/ Endangered Species 

The following mammals, birds, fish, and insects are federally endangered, threatened, proposed, 

and/or are listed as candidate species in Cleveland County, Oklahoma (US Fish and Wildlife 

Service [USFWS], 2022). 

• Mammals: Tricolored bat, Perimyotis subflavus (proposed endangered)

• Birds: Whooping crane, Grus americana (endangered); Red knot, Calidris canutus rufa

(threatened); Piping Plover, Charadrius melodus (threatened)

• Fish: Peppered chub, Macrhybopsis tetranema (endangered); Arkansas River shiner,

Notropis girardi (threatened)

• Insects: Monarch butterfly, Danaus plexippus (candidate)

2.3 History of PFAS Use 

Four AOIs were identified in the PA where AFFF may have been used, stored, disposed, or 

released historically at the Lexington AASF (AECOM, 2020). PFAS-containing materials were 

potentially released to surface soil within the boundary of Lexington AASF #1 through equipment 

discharge, accidental leaks and spills, and any potential undocumented fire suppression system 

testing. The potential release areas were grouped into four AOIs based on proximity to one 

another and presumed groundwater flow. These areas include:

• AOI 1: Northern Release Areas

• AOI 2: Eastern Release Areas

• AOI 3: Mobile Refueler Parking Area

• AOI 4: Fuel Point

AFFF may have historically been released at the Flight Line and Burn Pit (Northern Release 

Areas) during fire training activities sometime between the mid to late 1980s to as late as 2008. 

In the Eastern Release Areas, Hangar 2 houses a fire suppression system, installed in 2001, that 

is equipped with two 800-gallon tanks of 3% Military Specification AFFF and two 36-gallon AFFF 

tanks. Additional AFFF releases may also have occurred from incidental spills from AFFF storage, 

firetruck staging, nozzle testing, and the washing of firetrucks as early as 1986 to as late as 2007.

The Lagoons within the AOI 2 received discharge from the Old Wash Rack until 2004, when the 

Old Wash Rack was removed as part of Oklahoma ARNG (OKARNG) efforts to eliminate storm 

water drainage to the Lagoons. The holding tank overflow at Hangar 2 may discharge to the 

Lagoons. The Mobile Refueler Parking Area and Fuel Point were both used for storage of TriMaxTM 30 extinguishers to as late as 2008, when the units were removed from AASF #1. The 

potential release areas were grouped into four AOIs based on preliminary data and presumed 

groundwater flow directions. A description of each AOI is presented in Section 3. 
­12420 Milestone Center Drive

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Figure 2-1

Facility Location

Legend

Facility Boundary

0 0.5 1 2

Miles

Lexington AASF #1

^_

AECOM 2-5
­12420 Milestone Center Drive

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Boundaries Dataset, 3DEP Elevation Program,

Figure 2-2

Facility Topography

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­12420 Milestone Center Drive

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and the GIS User Community

Figure 2-3

Groundwater Features

Legend

Facility Boundary

Water Body

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Direction

Inferred Groundwater

Flow Direction

Geology

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Garber Sandstone

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AECOM 2-7
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 2-8

THIS PAGE INTENTIONALLY BLANK
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­ Figure 2-4

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1:4,320

Groundwater Elevations, April 2022

12420 Milestone Center Drive

Germantown, MD 20876

A! Monitoring Well

Facility Boundary

Water Body

River/Stream

Groundwater Elevation Contour

Inferred Groundwater Elevation Contour

Groundwater Flow Direction

0 180 360 720

Feet

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AECOM 2-9
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

THIS PAGE INTENTIONALLY BLANK

AECOM 2-10
Buckhead

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Lake-Canadian

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­12420 Milestone Center Drive

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and the GIS User Community

Figure 2-5

Surface Water Features

Legend

Facility Boundary

Water Body

River/Stream

Surface Water Flow Direction

0 0.25 0.5 1

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AECOM 2-11
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 2-12

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Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

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, 11 potential release areas were 

identified at Lexington AASF and grouped into four AOIs (AECOM, 2020). The potential release 

areas are shown on Figure 3-1. 

3.1 AOI 1 Northern Release Areas

AOI 1 consists of two potential release areas, as described below. Releases at AOI 1 have 

occurred on both paved areas and grassy surfaces. Some AFFF releases may have occurred 

directly onto surface soil but may also have infiltrated to the subsurface soil via cracks in pavement 

or joints between areas that are paved with different materials. Surface water flows westward via 

drainage ditches along the western side of the AASF #1 and into the unnamed tributary of 

Buckhead Creek.

3.1.1 Flight Line

The Flight Line is located in the central area of the AASF #1. Fire training activities were conducted 

with one or two Tri-MaxTM 30 extinguishers on the concrete of the Flight Line. The dates of AFFF 

releases are unknown, but the releases occurred sometime after the firetrucks were acquired in 

the mid to late 1980s and as late as 2008, when the Tri-MaxTM 30 extinguishers were removed 

from the AASF #1. AFFF released at the Flight Line may have flowed off to the grassy area directly 

to the west. 

3.1.2 Burn Pit

The Burn Pit is located west of the flight line and east of the autorotation zone, in the northern half 

of the facility. During fire training activities, firetrucks discharged AFFF at this location. No 

information was available on the concentration of AFFF used or when the fire training activities 

occurred. Around 1986, the AFFF-equipped firetruck with approximately 100-gallons of AFFF was 

used to put out a fire at the burn pit, but the firetruck caught fire and burned. Documentation was 

not available to determine the degree the firetruck was burned, but it is believed that the facility’s

second firetruck, equipped with Purple K, was used to put out the burning firetruck. Training 

activities on the ramp also included firetrucks equipped with only water and Tri-MaxTM 

extinguishers filled with Dawn® dish soap.

Surface soil in the northern part of the facility, including the Burn Pit, was cut down by 20 feet; the 

removed soil was used as cover in the immediate vicinity. Any remaining soil was stockpiled east 

of AOI 1, although much of it has been taken by Cleveland County for road construction. The 

surface soil remaining at the Burn Pit is native soil, but it is possibly feet below the grade of when 

the Burn Pit was operational.

3.2 AOI 2 Eastern Release Areas 

AOI 2 consists of seven potential release areas, as described below. Releases at AOI 2 have 

occurred on both paved areas and grassy surfaces. Some AFFF releases may have occurred 

directly onto surface soil but may also have infiltrated to the subsurface soil via cracks in pavement 

or joints between areas that are paved with different materials.
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 3-2

3.2.1 Hangar 2

Hangar 2 was constructed in 1999-2000 and is northeast of Hangar 1. Hangar 2 houses a fire 

suppression system equipped with two 800-gallon tanks of 3% Military Specification AFFF and 

two 36-gallon AFFF tanks, one on the north side of the hangar and one on the south side. The 

fire suppression system tanks are located in the mechanical room on the second floor of the 

hangar. The system was installed in 2001, and as of July 2012, it was reported that no spills or 

leaks had occurred. A contractor inspects the system every 6 months. In September 2013, the 

bladder in one of the 800-gallon tanks leaked and resulted in an AFFF spill on the mechanical 

room floor. After the spill, the contractor removed the remaining contents of the tank and disposed 

the AFFF at an offsite location. The bladder was subsequently replaced and refilled. Any releases

or spills in Hangar 2 would flow to the floor drains, which drain to an underground holding tank on 

the south side of the hangar. When the holding tank was originally installed, there was no 

drainpipe or overflow; however, OKARNG personnel indicated that the holding tank may have 

been retrofitted with an overflow. If the tank were to get too full, it would discharge via the overflow 

to the sanitary sewer and into the lagoons. The as-builts for the holding tank were never provided 

to the OKARNG by the contractor to confirm the presence of a drainage pipe. Personnel were not 

aware of the holding tank ever being full or serviced.

3.2.2 Old Fire Station

The Old Fire Station is located east of Hangar 1 and now serves as a maintenance shop. The Old 

Fire Station housed two firetrucks from before 1987 to 2006/2007. One of the firetrucks contained 

Purple K, while the second firetruck contained AFFF. According to interviews, the AFFF-equipped 

firetruck carried 20 5-gallon buckets of AFFF. No information was available on the concentration 

or type of AFFF used in the firetruck. The AFFF-equipped firetruck reportedly caught fire while 

carrying up to 100 gallons of AFFF near the Burn Pit. The firetruck was destroyed during the fire 

and replaced with a new AFFF-equipped firetruck. The arrival date of the new firetruck at AASF 

#1 is unknown. Additionally, no known leaks or spills of AFFF were reported.

The firetrucks reportedly trained with only water at the Burn Pit; however, during the PA,

interviewees indicated that AFFF was pumped from one of the firetrucks, although they were 

uncertain about the time and location of this event. It was also noted that fire crews tested the 

nozzles at the Old Wash Rack. 

3.2.3 Old Wash Rack

The Old Wash Rack is located between Hangar 1 and the Old Fire Station. Once a year, nozzle 

testing occurred at the Old Wash Rack from 1986 to 2004; however, it was not clear whether 

AFFF or only water were discharged during these tests. Fire training activities with the Tri-MaxTM 

30 units occurred twice at the Old Wash Rack. The dates of the training events are unknown, and 

no information was available on the concentration of AFFF used during these events. Additionally, 

the Old Wash Rack was used to wash vehicles, including the AFFF-equipped firetruck. The Old 

Wash Rack drained to the lagoons, but it was removed in 2004 to prevent storm water from 

entering the sanitary sewer system. A total of 23 Tri-MaxTM 30 extinguishers were maintained by 

a contractor at the facility and serviced every 6 years. When serviced, the AFFF removed from 

the extinguishers was discharged at the Old Wash Rack before being refilled. The 23 

extinguishers were serviced at least two times at the Old Wash Rack.

3.2.4 Grassy Area Behind Hangar 1

The Grassy Area Behind Hangar 1 is between the lagoons to the east and Hangar 1 to the west.

During one fire training event with a Tri-MaxTM 30 extinguisher, AFFF was released to the Grassy 
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AECOM 3-3

Area Behind Hangar 1. The date of the training event is unknown, and no information was 

available on the concentration of AFFF used during the event. 

3.2.5 Storage Building

The Storage Building is located directly east of the Old Fire Station. During the PA site visit, a 

265-gallon container of 3% AFFF was observed. It is unknown whether there were any historic 

spills or leaks. There are no floor drains in the Storage Building.

3.2.6 Old AFFF Storage Location

The Old AFFF Storage Location is located east of the Old Fire Station and south of Hangar 2. 

Historically, 25 5-gallon buckets of AFFF were stored at this location. No information was available 

on the concentration or type of AFFF stored in the buckets. No known leaks or spills were 

reported. The Old AFFF Storage Location is an open-sided building with no floor drains. 

3.2.7 Lagoons

The Lagoons are a two-cell sanitary sewer lagoon system and are located on the east side of 

AASF #1. The Lagoons are downslope of the Grassy Area Behind Hangar 1, Hangar 2, Old Fire 

Station, Old Wash Rack, and the Storage Building; however, berms around the Lagoons prevent 

any stormwater runoff from entering them. The berms direct stormwater to the south and east of 

the Lagoons to the intermittent tributary of Buckhead Creek. The Lagoons received discharge 

from the Old Wash Rack until 2004, when the Old Wash Rack was removed as part of OKARNG

efforts to eliminate storm water drainage to the Lagoons. The holding tank overflow at Hangar 2 

may discharge to the Lagoons. 

Wastewater at the Lagoons does not discharge to any other surface water body and eventually 

evaporates. The Lagoons were originally lined with a clay liner. Around 2006, the lagoon system 

was renovated. Additional clay was added to the liners to increase the thickness of clay, and a 

rubberized membrane was put on the sides and tops of the berms to discourage vegetation 

growth. The liners were noted to be torn in a number of places at the time of the PA site visit. 

During SI field activities, a leak was observed on the exterior of the dike at the southeast corner 

of the lagoons and was draining onto the adjacent lowland area. 

3.3 AOI 3 Mobile Refueler Parking Area

AOI 3 consists of one potential release area. The Mobile Refueler Parking Area is a concrete 

covered area west of Hangar 1. At least one Tri-MaxTM 30 extinguisher was historically stored at 

AOI 3 inside the secondary containment structure. No known or recorded leaks or spills occurred 

at AOI 3; however, any AFFF releases inside the containment structure would flow to an oil/water 

separator (OWS) and then toward the eastern side of the facility where the OWS discharges to 

the ground surface in the grassy area behind Hangar 1. Any AFFF release outside of the

secondary containment structure would flow westward, off the concrete, potentially impacting soil. 

Surface water at AOI 3 flows west toward the unnamed tributary of Buckhead Creek.

3.4 AOI 4 Fuel Point

AOI 4 consists of one potential release area. The Fuel Point is located in the southwestern portion 

of Lexington AASF #1 and houses four 20,000-gallon aboveground storage tanks. Historically, 

two Tri-MaxTM 30 extinguishers were stored at the Fuel Point, one at the southeast corner and 

one at the northwest corner. No information was available on the concentration or type of AFFF

in the Tri-MaxTM 30 extinguishers. No leaks or spills were recorded or noted by interviewees. AOI 
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4 has a concrete surface with two storm drains. AFFF releases at the Fuel Point would drain to 

the OWS. The OWS and storm drains channel water northward towards a small pond and an 

unnamed tributary of Buckhead Creek.
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AOI 2

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Site Inspection at Lexington AASF #1, OK

11/3/2022

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4. Project Data Quality Objectives

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

Assurance Project Plan (QAPP) Addendum (AECOM, 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 Lexington AASF #1 (AECOM, 2020); 

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

with the site-specific Uniform Federal Policy (UFP)-QAPP Addendum (AECOM, 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 Spring

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 

facility-specific DQOs. Both sampling and analytical activities are considered to assess whether 
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AECOM 4-2

the collected data are of the right type, quality, and quantity to support the decision-making (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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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, Lexington Army Aviation Support Facility #1,

Oklahoma dated October 2020 (AECOM, 2020);

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

Lexington Army Aviation Support Facility #1, Oklahoma dated September 2021 (AECOM,

2021);

• Final Site Safety and Health Plan, Lexington Army Aviation Support Facility #1, Oklahoma

dated March 2022 (AECOM, 2022).

The SI field activities were conducted from 6 to 22 April 2022 and consisted of utility clearance, 

rotary sonic (sonic) drilling, soil sample collection, permanent monitoring well installation, low-flow

groundwater sample collection, surface water sample collection, and land surveying. Field activities 

were conducted in accordance with the SI QAPP Addendum (AECOM, 2021), except as noted in 

Section 5.9. 

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:

• Thirty-four (34) soil samples from 24 locations;

• Five (5) low-flow groundwater samples from 5 permanent monitoring wells;

• Two (2) surface water samples from 2 surface water locations; and

• Twenty-two (22) 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, a Nonconformance and 

Corrective Action Report is provided in Appendix B3, land survey data are provided in Appendix 

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

5.1 Pre-Investigation Activities

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

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

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

5.1.1 Technical Project Planning

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

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

A combined TPP Meeting 1 and 2 was held on 18 August 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, OKARNG, USACE, and Oklahoma Department of 

Environmental Quality. 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 3 April 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 subcontractor, Environmental Works, Inc., contacted Oklahoma

811 (OKIE811) one-call utility clearance contractor prior to mobilization to notify them of intrusive 

work. Because OKIE811 locators do not locate private utilities, such as those belonging to 

Lexington AASF #1, 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 6 April 2022 using industry standard 

methods in addition to ground-penetrating radar. Additionally, the first 5 feet of each boring were 

pre-cleared using a hand auger to verify utility clearance in shallow subsurface where utilities 

would typically be encountered. 

5.1.3 Source Water and Sampling Equipment Acceptability

Two potable water sources at Lexington AASF #1 were sampled on 27 October 2021 to assess 

usability for decontamination of drilling equipment. Specifically, the samples were analyzed by 

LC/MS/MS compliant with QSM 5.3 Table B-15. A third decontamination water sample was 

collected from the same water source on 21 April 2022 after it had passed through the driller’s 

holding tank. The results of the decontamination water samples used during the SI are provided 

in Appendix F. The decontamination water samples collected in October 2021 displayed 

concentrations greater than the limit of detection for several target analytes. These results were 

evaluated prior to the SI mobilization, at which time the results were noted to be below 1/5 of the 

SLs at that time, as required by the SI QAPP Addendum (AECOM, 2021). As a result, the onfacility decontamination water was determined to be acceptable for use. Comparison of the results 

to the updated SLs shows the PFOS results for decontamination water samples LEX-DECON-01

and LEX-DECON-02 exceed 1/5 of the current SL. However, results for decontamination water 

sample LEX-DECON-03, collected during the April 2022 SI mobilization, were below 1/5 of the SL 

for all target compounds. Sample LEX-DECON-03 is more representative of all decontamination 

water and drilling water used during SI field activities. A discussion of these sample 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. 
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5.2 Soil Borings and Soil Sampling

Soil samples were collected via sonic drilling technology and hand auger in accordance with the 

SI QAPP Addendum (AECOM, 2021). A GeoProbe® 8150LS sonic 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 saturated soil, and one subsurface soil sample at the mid-point 

between the surface and saturated soil. To supplement the drilled boring locations, additional 

surface soil samples were collected at other locations using a hand auger.

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

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

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

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

During the SI, soil borings were completed to depths ranging between 20 to 65 feet bgs. Soils 

observed generally consisted of red to reddish brown silty sand and low plasticity fines (clay and 

silt), as well as minor concentrations of gravel. Interbedded deposits of caliche were observed in 

four of the five borings. Blocky textures, laminated bedding, and fissures, as well as remnant 

structures indicative of weathered rock, were observed in several borings during the SI; however,

competent bedrock was not encountered to depths up to 65 feet bgs. The silt, clay, sands, and 

minor concentrations of gravel are also consistent with Quaternary alluvial deposits environment 

overlying heavily weathered Garber Formation at the facility. 

Difficult drilling conditions at the original LEX-MW004 location caused the drill casing to seize in 

the borehole at a depth of 45 feet bgs. Multiple attempts were made over several days to free the 

casing through cooling and over drilling; however, the tooling could not be freed. The casing was 

disconnected to a depth of 10 feet bgs, and the borehole and interior of the stuck casing were 

abandoned using a cement-bentonite grout. Location LEX-MW004 was offset approximately 20 

feet and drilled, and the permanent monitoring well was installed. The location of the abandoned 

drill casing is shown on Figure 5-1. 

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 duplicates (MSDs) were collected at a rate 

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

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

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

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

preserved at or below 6 degrees Celsius (°C) during shipment.
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AECOM 5-4

Sonic borings were converted to permanent wells in accordance with the SI QAPP Addendum 

(AECOM, 2021). Borings were installed in grass areas to avoid disturbing concrete or asphalt 

surfaces.

5.3 Surface Water Sampling

Surface water samples were collected at AOI 2 within the two sanitary lagoons. AOI02-08-SW 

was collected from the northern lagoon, and AOI02-09-SW was collected from the southern 

lagoon. In accordance with the SI QAPP addendum, sediment samples were not collected due to 

health and safety concerns regarding the sanitary nature of sediments within the lagoons, and to 

avoid potential damage to the lagoon liners (AECOM, 2021). 

Surface water samples were collected from a single point near the bank of each lagoon by dipping 

the laboratory-supplied bottle into the water and filling from approximately halfway up the water 

column. Sampling was performed deliberately and methodically to avoid disturbance of bottom 

sediments and as quickly as possible to ensure a representative sample was collected. 

Additionally, a subsample of each surface water sample was collected in a separate container, 

and a shaker test was completed to identify if there were any foaming. No foaming was noted on 

any of the surface water subsamples.

After collection of the surface water samples from each location, general water quality parameters 

(i.e., temperature, pH, conductivity, dissolved oxygen [DO], and oxidation-reduction potential

[ORP]) were collected with a water quality meter and recorded on the field sampling form 

(Appendix B2). The surface water locations are shown on Figure 5-1, and sample information is

provided in Table 5-1. 

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

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

standard CoC procedures to the laboratory for analysis by LC/MS/MS compliant with QSM 5.1 

Table B-15. Sediment samples were also analyzed for TOC (USEPA Method 9060A) and pH 

(USEPA Method 9045D), 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/MSDs were collected at a rate of 5% and analyzed for the 

same parameters as the accompanying samples. A temperature blank was placed in each cooler 

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

5.4 Permanent Well Installation and Groundwater Sampling

During the SI, five permanent monitoring wells were installed within or downgradient of potential 

source areas. The locations of the wells are shown on Figure 5-2. 

A GeoProbe® 8150LS drill rig was used to install five 2-inch diameter monitoring wells. The 

monitoring wells were constructed with Schedule 40 PVC, flush threaded 10-foot sections of riser, 

0.010-inch slotted well screen, and a threaded bottom cap. A filter pack of #1 Filter Sand was 

installed in the annulus around the well screen to a minimum of 2 feet above the well screen. 

A 3- to 7-foot-thick bentonite seal was placed above the filter sand and hydrated in lifts with water. 

Bentonite-cement grout was placed in the well annulus from the top of the bentonite seal to ground 

surface. The bentonite-cement grout was allowed to set for 24 hours prior to well completion in 

accordance with the SI QAPP Addendum (AECOM, 2021). All monitoring wells were completed 

with flush mount well vaults set in concrete pads. The screen interval of each of the groundwater 

monitoring wells is provided in Table 5-2. 

Development and sampling of wells was completed in accordance with the SI QAPP Addendum 

(AECOM, 2021). The newly installed monitoring wells were developed no sooner than 24 hours 
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following installation by pumping and surging using a variable speed submersible pump. Samples 

were collected no sooner than 24 hours following development via low-flow sampling methods 

using a submersible or peristaltic pump with disposable PFAS-free, HDPE tubing. New tubing 

was used at each well, and the pumps were decontaminated between each well. The wells were 

purged at a rate determined in the field to reduce draw down prior to sampling. Water quality 

parameters (e.g., temperature, specific conductance, pH, DO, and ORP) were measured using a 

water quality meter and recorded on the field sampling form (Appendix B2). Water levels were 

measured to the nearest 0.01 inch and recorded. 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 subsamples.

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

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

standard CoC procedures to the laboratory and analyzed 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/MSDs 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 submersible 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.

5.5 Synoptic Water Level Measurements

A synoptic groundwater gauging event was performed on 22 April 2022. Groundwater elevation 

measurements were collected from the five new permanent monitoring wells. Water level 

measurements ranged between 12.75 to 51.08 feet bgs. A groundwater flow contour map is 

provided in Figure 2-4. Groundwater elevation data is provided in Table 5-3. 

5.6 Surveying 

The northern side of each well casing was surveyed by Oklahoma-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 21 April 2022 in the 

applicable North American Datum 1983 (NAD83, horizontal) in Oklahoma State Plane (3501) 

South Zone and North American Vertical Datum 1988 (NAVD88, vertical). The surveyed well data 

are provided in Appendix B3. 

5.7 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 six soil boring 

locations, including the abandoned LEX-MW004 location. No soil IDW was generated at the 

surface soil sample locations. The soil IDW generated during the SI activities were contained in

eight labeled, 55-gallon Department of Transportation (DOT)-approved steel drums and left onsite

in the northeast portion of the facility in the Connex Storage Yard, east of Hangar 2, pending 

laboratory analysis. The soil IDW was not sampled and assumes the PFAS characteristics of the 
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associated soil samples collected from that source location. ARNG will coordinate the

transportation and disposal of the solid IDW in accordance with the Army Guidance for Addressing 

Releases of PFAS, Q18 (DA, 2018).

Liquid IDW generated during SI activities (i.e., purge water, development water, and 

decontamination fluids) were contained in two labeled, 55-gallon DOT-approved steel drums, and 

left onsite within the Connex Storage Yard pending laboratory analysis. Due to the minimal 

amount of IDW generated, liquid IDW from all locations was consolidated into two drums. The 

liquid IDW was not sampled and assumes the characteristics of the associated groundwater 

samples collected from that source location. ARNG will further manage liquid IDW in accordance 

with the Army Guidance for Addressing Releases of PFAS, Q18 (DA, 2018). Based on laboratory 

results, containerized liquid IDW will be managed and disposed by ARNG (either by offsite 

disposal or onsite disposal, with treatment as appropriate) under a separate contract in 

accordance with SOP No. 042A for Treating Liquid Investigation-Derived Material (Purge water, 

drilling water, and decontamination fluids) (EA Engineering, Science, and Technology, Inc., 2021).

ARNG will further coordinate to ensure proper disposal in accordance with state requirements 

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

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

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

activities were disposed of at a licensed solid waste landfill.

5.8 Laboratory Analytical Methods

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

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

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

5.9 Deviations from the SI QAPP Addendum

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

documentation. The deviation is noted below and is documented in a Nonconformance and 

Corrective Action Report (Appendix B3): 

• During sonic drilling activities, the mid-point subsurface soil sample was collected from 19

to 20 feet bgs at boring LEX-MW001. The approved SI QAPP Addendum states that midpoint subsurface soil samples would be collected from 13 to 15 feet bgs if depth to water

were greater than 30 feet bgs. Water was encountered at approximately 40 feet bgs during

drilling, and the mid-point samples were inadvertently collected at depths greater than 15

feet bgs. Consequently, the analytical results of the collected mid-point sample (19 to 20

feet bgs), as well as the surface soil samples at AOI 1, were used to make conservative

assumptions for the CSM. This action was documented in a nonconformance and corrective

action report provided in Appendix B3.
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, Lexington AASF #1, Oklahoma

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 4/12/2022 0-2 x

AOI01-02-SB-00-02 4/12/2022 0-2 x x x

AOI01-02-SB-00-02-MS 4/12/2022 0-2 x x MS/MSD

AOI01-02-SB-00-02-MSD 4/12/2022 0-2 x x MS/MSD

AOI01-03-SB-00-02 4/12/2022 0-2 x

AOI01-04-SB-00-02 4/14/2022 0-2 x

AOI01-04-SB-00-02-D 4/14/2022 0-2 x Duplicate

AOI01-05-SB-00-02 4/14/2022 0-2 x

AOI01-06-SB-00-02 4/14/2022 0-2 x

AOI01-07-SB-00-02 4/14/2022 0-2 x

AOI01-08-SB-00-02 4/14/2022 0-2 x

AOI01-09-SB-00-02 4/14/2022 0-2 x

AOI01-10-SB-00-02 4/14/2022 0-2 x

AOI02-01-SB-00-02 4/12/2022 0-2 x

AOI02-02-SB-00-02 4/15/2022 0-2 x

AOI02-03-SB-00-02 4/12/2022 0-2 x

AOI02-04-SB-00-02 4/12/2022 0-2 x x x

AOI02-04-SB-00-02-D 4/12/2022 0-2 x x Duplicate

AOI02-05-SB-00-02 4/15/2022 0-2 x

AOI02-06-SB-00-02 4/15/2022 0-2 x

AOI02-07-SB-00-02 4/15/2022 0-2 x

AOI03-01-SB-00-02 4/14/2022 0-2 x x x

AOI03-01-SB-00-02-D 4/14/2022 0-2 x Duplicate

AOI04-01-SB-00-02 4/12/2012 0-2 x x x

AOI04-01-SB-00-02-D 4/12/2012 0-2 x Duplicate

LEX-MW001-SB-00-02 4/12/2022 0-2 x

LEX-MW001-SB-19-20 4/20/2022 19-20 x

LEX-MW001-SB-19-20-MS 4/20/2022 19-20 x MS/MSD

LEX-MW001-SB-19-20-MSD 4/20/2022 19-20 x MS/MSD

LEX-MW001-SB-39-40 4/20/2022 39-40 x

LEX-MW001-SB-34-35 4/20/2022 34-35 x

LEX-MW002-SB-00-02 4/12/2022 0-2 x

LEX-MW002-SB-09-10 4/15/2022 9-10 x

LEX-MW002-SB-11-12 4/15/2022 11-12 x

LEX-MW002-SB-19-20 4/15/2022 19-20 x

LEX-MW003-SB-00-02 4/15/2022 0-2 x

LEX-MW003-SB-00-02-D 4/15/2022 0-2 x Duplicate

LEX-MW003-SB-05-06 4/15/2022 5-6 x

LEX-MW003-SB-10-11 4/15/2022 10-11 x

LEX-MW004-SB-00-02 4/18/2022 0-2 x

LEX-MW004-SB-14-15 4/19/2022 14-15 x

LEX-MW004-SB-28-29 4/19/2022 28-29 x

LEX-MW005-SB-00-02 4/15/2022 0-2 x

LEX-MW005-SB-14-15 4/19/2022 14-15 x

LEX-MW005-SB-14-15-MS 4/19/2022 14-15 x MS/MSD

LEX-MW005-SB-14-15-MSD 4/19/2022 14-15 x MS/MSD

LEX-MW005-SB-59-60 4/19/2020 59-60 x

LEX-MW005-SB-34-35 4/19/2022 34-35 x

Soil Samples

AECOM 5-7
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, Lexington AASF #1, Oklahoma

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

LEX-MW001-042222 4/22/2022 NA x

LEX-MW001-042222-MS 4/22/2022 NA x MS/MSD

LEX-MW001-042222-MSD 4/22/2022 NA x MS/MSD

LEX-MW002-042122 4/21/2022 NA x

LEX-MW003-042122 4/21/2022 NA x

LEX-MW003-042122-D 4/21/2022 NA x Duplicate

LEX-MW004-042222 4/22/2022 NA x

LEX-MW005-042222 4/22/2022 NA x

AOI02-08-SW 4/20/2022 NA x

AOI02-08-SW-D 4/20/2022 NA x Duplicate

AOI02-08-SW-MS 4/20/2022 NA x MS/MSD

AOI02-08-SW-MSD 4/20/2022 NA x MS/MSD

AOI02-09-SW 4/20/2022 NA x

LEX-FRB-01 4/21/2022 NA x

LEX-ERB-01 4/12/2022 NA x

LEX-ERB-02 4/15/2022 NA x

LEX-ERB-03 4/21/2022 NA x

LEX-ERB-04 4/22/2022 NA x

LEX-DECON-01 10/27/2021 NA x

LEX-DECON-02 10/27/2021 NA x

LEX-DECON-03 4/21/2022 NA x

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

Blank Samples

Groundwater Samples

Surface Water Samples

AECOM 5-8
Area of 

Interest

Boring 

Location

Monitoring 

Well ID

Soil Boring 

Depth 

(feet bgs)

Permanent Well 

Screen Interval 

(feet bgs)

1 LEX-MW001 LEX-MW001 50 35-45

LEX-MW002 LEX-MW002 30 19.6-29.6LEX-MW003 LEX-MW003 20 8-18LEX-MW004 LEX-MW004 37 25-35LEX-MW005 LEX-MW005 65 55-65

Notes:

AASF = Army Aviation Support Facility

bgs = below ground surfaceLEX = LexingtonID = identification

2

Table 5-2

Soil Boring Depths and Permanent Well Screen Intervals

Site Inspection Report, Lexington AASF #1, Lexington, Oklahoma

AECOM 
Table 5-3

Depths to Water and Groundwater Elevations in Permanent Wells

Site Inspection Report, Lexington AASF #1, Lexington, Oklahoma

Location ID

Permanent Well 

Screen Interval 

(feet bgs)

Top of Casing

Elevation 

(feet NAVD88)

Ground Surface 

Elevation 

(feet NAVD88)

Depth to Water 

(feet btoc)

Depth to Water

feet bgs)

Groundwater 

Elevation 

(feet NAVD88)

LEX-MW001 35-45 1099.13 1099.48 38.22 38.57 1060.91

LEX-MW002 19.6-29.6 1080.64 1080.91 20.02 20.29 1060.62

LEX-MW003 8-18 1072.81 1073.28 12.28 12.75 1060.53

LEX-MW004 25-35 1078.71 1079.01 23.78 24.08 1054.93

LEX-MW005 55-65 1099.17 1099.47 50.78 51.08 1048.39

Notes:

AASF = Army Aviation Support Facility

bgs = below ground surface

btoc = below top of casing

ID = identification

NAVD88 = North American Vertical Datum 1988

AECOM 5-10
"S

"S

A!

"S

A!

"S

A!

"S

"S "S

"S "S

"S

"S

"S

"S

A!

"S

"J

"J

A!

"S

"S

"S

"S

"S

"

Oklahoma 

Department of 

Corrections/AASF #1 

Supply Well

Grassy Area

Behind Hangar 1

Old Wash Rack

Flight Line

Burn Pit

Fuel Point

Mobile Refueler

Parking Area

Lagoons Old Fire Station

Storage Building

Old AFFF Storage Location

Hangar 2

AOI 4

AOI 3

AOI 2

AOI 1

AOI01-04

AOI01-05

LEX-MW005

AOI03-01

LEX-MW003

AOI01-01

LEX-MW001

AOI01-02

AOI01-06 AOI01-07

AOI01-09

AOI01-08

AOI01-03

AOI02-01

AOI02-02

AOI02-03

LEX-MW002

AOI02-04

AOI02-08

AOI02-09

LEX-MW004

AOI04-01

AOI02-07

AOI02-06

AOI02-05

AOI01-10

Abandoned Drill Casing

0 175 350 700

Feet

­ Figure 5-1

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Lexington AASF #1, OK

1/9/2023

1/9/2023

1/9/2023

MS

MC

CM

GIS BY

CHK BY

PM

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

1/9/2023

1:4,200

Site Inspection Sample Locations

12420 Milestone Center Drive

Germantown, MD 20876

A! Monitoring Well

"S Surface Soil Sample

"J Surface Water

" Abandoned Drill Casing

Area of Interest

Potential Release Area

Facility Boundary

Surface Water Flow Direction

Inferred Groundwater Flow Direction

Groundwater Flow Direction

Alluvium

Garber Sandstone

AECOM 5-11
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

THIS PAGE INTENTIONALLY BLANK

AECOM 5-12
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

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 6.5. Table 6-2 through Table 6-6 present results in soil, groundwater, or surface 

water 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

Lexington AASF #1, Lexington, Oklahoma

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: Northern Release Areas. 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 from AOI01-01 to AOI01-10 and LEX-MW001. Deep 

subsurface soil was sampled from LEX-MW001 (19 to 20 feet bgs and 39 to 40 feet bgs). As 

discussed in Section 5.9, shallow subsurface soil samples, defined as samples collected between 

2 and 15 feet bgs for comparison to the industrial/commercial worker SL, were not collected at 

LEX-MW001. 

AOI01-01, AOI01-02, and LEX-MW001 were collected in the vicinity of the Burn Pit. AOI01-04, 

AOI01-05, and AOI01-10 were located across the taxiway south of the burn pit. In the vicinity of 

the Flight Line fire training area, AOI01-06 and AOI01-08 were located to the west, while AOI01-

07 and AOI01-09 were located to the east. AOI01-03 was located in the dry swale west-southwest

of AOI 1, where most of the surface runoff from AOI 1 appeared to flow before accumulating in a 

ditch. 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 AOI 1, at concentrations 

below the SLs. PFOS was generally the highest relevant compound detected in surface soil at 

AOI 1, with a maximum concentration of 9.37 micrograms per kilogram (μg/kg) at LEX-MW001.

With the exception of PFNA at AOI01-01 (1.83 μg/kg), all other relevant compounds detected 

were below 1 μg/kg. 

In deep subsurface soil (> 15 feet bgs), PFOA, PFOS, PFHxS, and PFNA were detected. The 

maximum concentration detected was PFOA, at 1.53 μg/kg at LEX-MW001 (19 to 20 feet bgs).

6.3.2 AOI 1 Groundwater Analytical Results

Groundwater was sampled from LEX-MW001. Figure 6-6 and Figure 6-7 present the ranges of 

detections in groundwater. Table 6-5 summarizes the groundwater results. 
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 6-3

PFOS exceeded the 4 nanograms per liter (ng/L) SL, at a concentration of 7.93 ng/L at LEXMW001. PFOA, PFBS, PFHxS, and PFNA were detected below their SLs, at concentrations of 

5.07 ng/L, 2.56 J ng/L, 8.90 ng/L, and 2.54 J ng/L, respectively.

6.3.3 AOI 1 Conclusions

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

below their SLs. PFOS was detected in groundwater, at concentrations above the SL. Based on 

the exceedance of the SL for PFOS 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: Eastern Release Areas. The results for the surface water samples are also presented. The 

results in soil, groundwater, and surface water are summarized on Table 6-2 through Table 6-6. 

Soil, groundwater, and surface water results are presented on Figure 6-1 through Figure 6-9. 

6.4.1 AOI 2 Soil Analytical Results

Surface soil was sampled from 0 to 2 feet bgs from AOI02-01 to AOI02-07 and LEX-MW002 to 

LEX-MW005. Soil was also sampled from the shallow subsurface soil (9 to 15 feet bgs) from LEXMW002 to LEX-MW005 and deep subsurface soil (19 to 60 feet bgs) from LEX-MW002, LEXMW004, and LEX-MW005. 

LEX-MW002, AOI02-01, AOI02-03, AOI02-04, and AOI02-07 were located in the Grassy Area 

Behind Hangar 1. AOI02-02, AOI02-05, AOI02-06, and AOI02-08 were located east and 

downslope of Hangar 2. LEX-MW003 was located east of the Lagoons, between AOI 2 and the 

Oklahoma Department of Corrections/AASF #1 Supply Well. LEX-MW004 was located south of 

AOI 2, and LEX-MW005 was located southwest of AOI 2. LEX-MW005 was not associated with 

a specific AOI in the SI QAPP Addendum; however, it is now linked to AOI 2 based on the 

observed groundwater flow direction during the SI. 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. 

PFOS exceeded the SL in surface soil. PFOA, PFHxS, and PFNA were detected below their SLs 

in surface and subsurface soil, and PFOS was detected below the SL in subsurface soil. PFBS 

was not detected in soil at AOI 2. 

In surface soil at AOI 2, PFOS was detected above the 13 μg/kg SL at AOI02-03 (22.6 μg/kg), 

AOI02-07 (15.3 μg/kg), and LEX-MW003 (22.8 μg/kg). PFOA, PFHxS, and PFNA were detected 

at concentrations below their SLs. The maximum concentration detected of these three 

compounds was PFOA at 7.43 μg/kg at AOI02-05. PFBS was not detected in surface soil.

In shallow subsurface soil, PFOA, PFOS, PFHxS, and PFNA were detected at concentrations 

below their SLs. The maximum concentration detected of these four compounds was PFOS at 

37.6 μg/kg at LEX-MW003 (5 to 6 feet bgs). PFBS was not detected in shallow subsurface soil.

In deep subsurface soil, PFOA and PFHxS were detected at only one location, LEX-MW002 (19 

to 20 feet bgs), at concentrations of 0.103 J μg/kg and 0.810 J μg/kg. No other detections of 

PFOA, PFOS, PFBS, PFHxS, or PFNA were reported. Soil was not sampled in the deep 

subsurface soil interval (> 15 feet bgs) at LEX-MW003 because groundwater was encountered 

above this depth. The intermediate and deep soil samples from LEX-MW003 are captured in the 

shallow subsurface results. 
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 6-4

6.4.2 AOI 2 Groundwater Analytical Results

Groundwater was sampled from LEX-MW002 to LEX-MW005. Figure 6-6 and Figure 6-7 present 

the ranges of detections in groundwater. Table 6-5 summarizes the groundwater results. 

PFOA, PFOS, and PFHxS were detected in groundwater, at concentrations exceeding their SLs. 

PFBS and PFNA were detected below their SLs. 

PFOA was detected above the 6 ng/L SL, at concentrations of 250 ng/L at LEX-MW002 and 804 

ng/L at LEX-MW003. PFOS was detected above the 4 ng/L SL, at a concentration of 18.8 ng/L at 

LEX-MW003. PFHxS was detected above the 39 ng/L SL, at concentrations of 2,680 ng/L at LEXMW002 and 4,220 ng/L at LEX-MW003. No exceedances were observed at LEX-MW004 and 

LEX-MW005.

PFBS and PFNA were detected below the SLs, at maximum concentrations of 190 ng/L and 1.46 

J ng/L, respectively. Both maximum concentrations were detected at LEX-MW003.

6.4.3 AOI 2 Surface Water Analytical Results

Surface water was sampled along the shoreline of the two lagoons. AOI02-08-SW was collected 

from the northern lagoon, and AOI02-09-SW was collected from the southern lagoon. Figure 6-8

and Figure 6-9 present the ranges of detections in surface water. Table 6-6 summarizes the 

surface water results. 

PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in both surface water samples. PFOA 

was reported at a maximum concentration of 203 ng/L at AOI02-09. PFOS was reported at a 

maximum concentration of 80.0 ng/L at AOI02-09. PFBS was reported at a maximum 

concentration of 26.4 ng/L at AOI02-09. PFHxS was reported at a maximum concentration of 231 

ng/L at AOI02-09. PFNA was reported at a maximum concentration of 29.4 ng/L at AOI02-08.

There are no established SLs for surface water; therefore, the results are only used to inform the 

CSM. 

6.4.4 AOI 2 Conclusions

Based on the results of the SI, PFOS was detected in soil, above the SL. PFOA, PFOS, and 

PFHxS were detected in groundwater, at concentrations above their SLs. PFOA, PFOS, PFBS, 

PFHxS, and PFNA were also detected in surface water samples collected at AOI 2. Based on the 

exceedances of the SLs in soil and groundwater, further evaluation at AOI 2 is warranted. 

6.5 AOI 3 

This section presents the analytical results for surface soil in comparison to SLs for AOI 3: Mobile 

Refueler Parking Area. The results in surface soil are presented in Table 6-2. Soil results are 

presented on Figure 6-1 through Figure 6-4. Subsurface soil and groundwater were not sampled 

at AOI 3, consistent with the sampling plan provided in the SI QAPP Addendum (AECOM, 2021). 

6.5.1 AOI 3 Soil Analytical Results

Surface soil was sampled from 0 to 2 feet bgs at AOI03-01. AOI03-01 was located north of the 

Mobile Refueler Area, within the stormwater flow path. Figure 6-1 through Figure 6-5 present the 

ranges of detections in soil. Table 6-2 summarizes the soil results. 

In surface soil, PFOS was detected above the 13 μg/kg SL, at a concentration of 18.5 μg/kg. 

PFOA, PFHxS, and PFNA were detected below their SLs, at concentrations less than 1 μg/kg. 

PFBS was not detected in surface soil.
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 6-5

6.5.2 AOI 3 Conclusions

Based on the results of the SI, PFOS was detected in surface soil, above the SL. Subsurface soil 

and groundwater were not sampled. Based on the exceedances of the SL for PFOS in surface 

soil, further evaluation at AOI 3 is warranted.

6.6 AOI 4 

This section presents the analytical results for soil in comparison to SLs for AOI 4: Fuel Point. The 

results in soil are presented in Table 6-2. Soil results are presented on Figure 6-1 through 

Figure 6-4. Subsurface soil and groundwater were not sampled at AOI 4, consistent with the 

sampling plan provided in the SI QAPP Addendum (AECOM, 2021). 

6.6.1 AOI 4 Soil Analytical Results

Surface soil was sampled from 0 to 2 feet bgs at AOI04-01. AOI04-01 was located at the surface 

discharge of the OWS storm drains at the Fuel Point. Figure 6-1 through Figure 6-5 present the 

ranges of detections in soil. Table 6-2 summarizes the soil results. 

In surface soil at AOI 4, PFOA, PFOS, PFHxS, and PFNA were detected at concentrations at 

least one order of magnitude below their SLs. The maximum concentration detected of these four 

compounds was PFOS, at 1.30 μg/kg. PFBS was not detected in surface soil.

6.6.2 AOI 4 Conclusions

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

at least one order of magnitude below their SLs. Subsurface soil and groundwater were not 

sampled. Based on the detections below the SLs in soil, further evaluation at AOI 4 is not

warranted.
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 6-6

THIS PAGE INTENTIONALLY BLANK
Table 6-2

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

Site Inspection Report, Lexington AASF #1

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Re

PFBS 1900 ND U 0.048 J ND U 0.029 J ND UJ ND U ND U ND U 0.094 PFHxS 130 0.112 J 0.583 J 0.130 J 0.146 J 0.071 J ND U 0.053 J 0.229 J 0.172 PFNA 19 1.83 0.287 J 0.092 J ND UJ 0.030 J 0.057 J ND U 0.105 J 0.142 

PFOA 19 0.566 J 0.363 J 0.100 J ND U ND U ND U ND U 0.219 J 0.328 PFOS 13 6.09 2.14 1.94 0.486 J 0.453 J 0.271 J ND U 0.330 J 0.324 

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acidPFOA perfluorooctanoic acidPFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AASF Army Aviation Support FacilityU = The analyte was not detected at a level greater than or equal to the adjusted DL AOI Area of InterestUJ = 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 feetND = Analyte not detected above the LOD. LOD values are presented in Appendix F. HQ hazard quotient

ID identificationLCMSMS liquid chromatography with tandem LEX LexingtonLOD limit of detectionND analyte not detected above the LODOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierSB soil boringUSEPA United States Environmental Protecμg/kg micrograms per kilogram

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

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

AOI01-07-SB-00-02

04/14/2022

0-2 ft

AOI

AOI01-05-SB-00-02

04/14/2022

0-2 ft

AOI01-06-SB-00-02

04/14/2022

0-2 ft

AOI01-04-SB-00-02

04/14/2022

0-2 ft

AOI01-04-SB-00-02-D

04/14/2022

0-2 ft

AOI01-02-SB-00-02

04/12/2022

0-2 ft

AOI01-03-SB-00-02

04/12/2022

0-2 ft

Area of Interest

Sample ID

Sample Date

Depth

AOI01-01-SB-00-02

04/12/2022

0-2 ft

AECOM 
Table 6-2

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

Site Inspection Report, Lexington AASF #1

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual R

PFBS 1900 ND U ND U ND U ND U ND U ND U ND U ND U ND PFHxS 130 ND U 0.237 J ND U 0.144 J 0.181 J 0.109 J+ 0.153 J 0.125 J 0.34PFNA 19 ND U 0.556 J 0.111 J 0.758 J 0.927 J 0.212 J 1.90 1.55 0.15PFOA 19 ND U 0.265 J 0.112 J 0.459 J 0.177 J 0.106 J 7.43 1.54 0.12PFOS 13 ND U 9.37 1.53 6.07 22.6 2.71 0.982 J 3.43 15.3 

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acidPFOA perfluorooctanoic acidPFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AASF Army Aviation Support FacilityU = The analyte was not detected at a level greater than or equal to the adjusted DL AOI Area of InterestUJ = 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 feetND = Analyte not detected above the LOD. LOD values are presented in Appendix F. HQ hazard quotient

ID identificationLCMSMS liquid chromatography with tandem LEX LexingtonLOD limit of detectionND analyte not detected above the LOOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierSB soil boringUSEPA United States Environmental Proteμg/kg micrograms per kilogram

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

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

AOI02-06-SB-00-02

04/15/2022

0-2 ft

AO

AOI02-04-SB-00-02

04/12/2022

0-2 ft

AOI02-05-SB-00-02

04/15/2022

0-2 ft

AOI02-02-SB-00-02

04/15/2022

0-2 ft

AOI02-03-SB-00-02

04/12/2022

0-2 ft

LEX-MW001-SB-00-02

04/12/2022

0-2 ft

AOI02-01-SB-00-02

04/12/2022

0-2 ft

Area of Interest

Sample ID

Sample Date

Depth

AOI01-10-SB-00-02

04/14/2022

0-2 ft

AECOM 
Table 6-2

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

Site Inspection Report, Lexington AASF #1

Analyte OSD Screening 

Level a

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

PFBS 1900 ND U ND U ND U ND U ND U ND U ND U ND UPFHxS 130 0.230 J 0.244 J 0.052 J 0.242 J 0.363 J 0.467 J 0.033 J ND UJPFNA 19 0.466 J 0.535 J 0.031 J 0.031 J 0.155 J 0.205 J 0.091 J 0.115 JPFOA 19 0.362 J 0.424 J 0.089 J ND U 0.221 J 0.278 J 0.096 J 0.129 JPFOS 13 21.9 22.8 0.422 J 0.657 J 14.4 18.5 1.13 1.30

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic ac

References PFHxS perfluorohexanesulfonic ac

PFNA perfluorononanoic acidPFOA perfluorooctanoic acidPFOS perfluorooctanesulfonic ac

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AASF Army Aviation Support FacU = The analyte was not detected at a level greater than or equal to the adjusted DL AOI Area of InterestUJ = 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 feetND = Analyte not detected above the LOD. LOD values are presented in Appendix F. HQ hazard quotient

ID identificationLCMSMS liquid chromatography with LEX LexingtonLOD limit of detectionND analyte not detected above OSD Office of the Secretary of DQSM Quality Systems ManualQual interpreted qualifierSB soil boringUSEPA United States Environmentμg/kg micrograms per kilogram

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.

AOI03 AOI04

LEX-MW005-SB-00-02

04/15/2022

0-2 ft

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

AOI04-01-SB-00-02

04/12/2022

0-2 ft

AOI04-01-SB-00-02-D

04/12/2022

0-2 ft

AOI03-01-SB-00-02

04/14/2022

0-2 ft

AOI03-01-SB-00-02-D

04/14/2022

0-2 ft 0-2 ft

04/18/2022

Area of Interest

Sample ID

Sample Date

Depth

LEX-MW003-SB-00-02

04/15/2022

0-2 ft

AOI02

LEX-MW003-SB-00-02-D

04/15/2022

0-2 ft

LEX-MW004-SB-00-02

AECOM 
Table 6-3

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

Site Inspection Report, Lexington AASF #1

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual Result Qual

PFBS 25000 ND U ND U ND U ND U ND UPFHxS 1600 0.052 J 2.06 1.44 ND UJ ND U

PFNA 250 ND U 1.56 ND U ND UJ ND U

PFOA 250 ND U 1.64 0.504 J ND UJ ND UPFOS 160 ND U 37.6 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 acidPFOA perfluorooctanoic acidPFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AASF Army Aviation Support FaciliU = The analyte was not detected at a level greater than or equal to the adjusted DL AOI Area of InterestUJ = 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. DL detection limit

ft feet

Notes HQ hazard quotient

ND = Analyte not detected above the LOD. LOD values are presented in Appendix F. ID identification

LCMSMS liquid chromatography with taLOD limit of detectionND analyte not detected above tOSD Office of the Secretary of DeQSM Quality Systems ManualQual interpreted qualifierSB soil boringUSEPA United States Environmentaμg/kg micrograms per kilogram

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.

LEX-MW004-SB-14-15

04/19/2022

14-15 ft

LEX-MW005-SB-14-15

04/19/2022

14-15 ft

LEX-MW003-SB-05-06

04/15/2022

5-6 ft

LEX-MW003-SB-10-11

04/15/2022

10-11 ft

LEX-MW002-SB-09-10

AOI02

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

Area of Interest

Sample ID

Sample Date

Depth

04/15/2022

9-10 ft

AECOM 
Table 6-4

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

Site Inspection Report, Lexington AASF #1

Area of Interest

Sample ID

Sample Date

Depth

Analyte Result Qual Result Qual Result Qual Result Qual Result Qual

PFBS ND U ND U ND U ND U ND UPFHxS 1.26 ND U 0.810 J ND U ND U

PFNA 0.065 J ND U ND U ND U ND UPFOA 1.53 ND U 0.103 J ND U ND U

PFOS 0.233 J ND U ND U ND U ND U

Interpreted Qualifiers Chemical AbbreviationsJ = Estimated concentration PFBS perfluorobutanesulfonic acidU = 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 acidND = Analyte not detected above the LOD. LOD values are presented in Appendix F. PFOS perfluorooctanesulfonic acid

Acronyms and Abbreviations

AASF Army Aviation Support FacilityAOI Area of InterestDL detection limitft feetID identificationLCMSMS liquid chromatography with tandem LEX LexingtonLOD limit of detectionND analyte not detected above the LODQSM Quality Systems ManualQual interpreted qualifierSB soil boringμg/kg micrograms per kilogram

AOI02

LEX-MW005-SB-59-60

04/19/2022

59-60 ft

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

AOI01

LEX-MW002-SB-19-20

04/15/2022

19-20 ft

LEX-MW004-SB-28-29

04/19/2022

28-29 ft

LEX-MW001-SB-19-20

04/20/2022

19-20 ft

LEX-MW001-SB-39-40

04/20/2022

39-40 ft

AECOM 
Table 6-5

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

Site Inspection Report, Lexington AASF #1

Analyte OSD Screening 

Level a

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

PFBS 601 2.56 J 141 190 181 3.72 J 8.28PFHxS 39 8.90 2680 4220 4090 9.13 3.58 JPFNA 6 2.54 J ND U 1.46 J 1.36 J ND U ND UPFOA 6 5.07 250 804 786 ND U ND U

PFOS 4 7.93 ND U 18.8 16.9 ND U ND U

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acidPFOA perfluorooctanoic acidPFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

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

D duplicate

Notes DL detection limit

ND = Analyte not detected above the LOD. LOD values are presented in Appendix F. GW groundwater

HQ hazard quotientID identificationLCMSMS liquid chromatography with tandeLEX LexingtonLOD limit of detectionND analyte not detected above the LOOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierUSEPA United States Environmental Protng/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.

LEX-MW003-042122-D

04/21/2022

LEX-MW004-042222

04/22/2022

LEX-MW002-042122

04/21/2022

LEX-MW003-042122

04/21/2022

Sample ID

Sample Date

Area of Interest AOI01

LEX-MW001-042222

04/22/2022

AOI02

LEX-MW005-042222

04/22/2022

AECOM 
Table 6-6

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

Site Inspection Report, Lexington AASF #1

Area of Interest

Sample ID

Sample Date

Analyte Result Qual Result Qual Result Qual

PFBS 10.0 10.7 26.4PFHxS 67.8 74.2 231PFNA 26.8 29.4 25.2PFOA 76.0 83.1 203

PFOS 72.2 78.9 80.0

Notes Chemical AbbreviationsND = Analyte not detected above the LOD. LOD values are presented in Appendix F. PFBS perfluorobutanesulfonic acid

PFHxS perfluorohexanesulfonic acidPFNA perfluorononanoic acidPFOA perfluorooctanoic acidPFOS perfluorooctanesulfonic acidAcronyms and Abbreviations

AASF Army Aviation Support FacilityAOI Area of InterestD duplicateDL detection limitID identificationLCMSMS liquid chromatography with tandem mass LOD limit of detectionND analyte not detected above the LODQSM Quality Systems ManualQual interpreted qualifierng/l nanogram per literSW surface water

AOI02-09-SW

04/20/2022

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

AOI02

AOI02-08-SW

04/20/2022

AOI02-08-SW-D

04/20/2022

AECOM 
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

THIS PAGE INTENTIONALLY BLANK

AECOM 
LEX-MW005

LEX-MW003

LEX-MW001

LEX-MW002

LEX-MW004

AOI01-04

AOI01-05

LEX-MW005

AOI03-01

LEX-MW003

AOI01-01

LEX-MW001

AOI01-02

AOI01-06 AOI01-07

AOI01-09

AOI01-03 AOI01-08

AOI02-01

AOI02-02

AOI02-03

LEX-MW002

AOI02-04

LEX-MW004

AOI04-01

AOI02-07

AOI02-06

AOI02-05

AOI01-10

­ Figure 6-1

CLIENT

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PROJECT

ARNG

Site Inspection at Lexington AASF #1, OK

9/21/2022

9/21/2022

9/21/2022

MS

MC

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GIS BY

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

9/21/2022

1:5,400

PFOA Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

Legend

Facility Boundary

Groundwater Flow Direction

LEX-MW005

LEX-MW003

LEX-MW001

LEX-MW002

LEX-MW004

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

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

0 225 450 900

Feet

PFOA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

Shallow Intermediate Deep

AECOM 6-15
LEX-MW005

LEX-MW003

LEX-MW001

LEX-MW002

LEX-MW004

AOI01-04

AOI01-05

LEX-MW005

AOI03-01

LEX-MW003

AOI01-01

LEX-MW001

AOI01-02

AOI01-06 AOI01-07

AOI01-08 AOI01-09

AOI01-03

AOI02-01

AOI02-02

AOI02-03

LEX-MW002

AOI02-04

LEX-MW004

AOI04-01

AOI02-07

AOI02-06

AOI02-05

AOI01-10

­ Figure 6-2

CLIENT

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ARNG

Site Inspection at Lexington AASF #1, OK

9/21/2022

9/21/2022

9/21/2022

MS

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GIS BY

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

9/21/2022

1:5,400

PFOS Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

Legend

Facility Boundary

Groundwater Flow Direction

LEX-MW005

LEX-MW003

LEX-MW001

LEX-MW002

LEX-MW004

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

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

0 225 450 900

Feet

Shallow Intermediate Deep

PFOS Results (μg/Kg)

ND

>ND - 13

>13 - 160

>160 - 1,600

>1,600

AECOM 6-16
LEX-MW005

LEX-MW003

LEX-MW001

LEX-MW002

LEX-MW004

AOI01-04

AOI01-05

LEX-MW005

AOI03-01

LEX-MW003

AOI01-01

LEX-MW001

AOI01-02

AOI01-06 AOI01-07

AOI01-08 AOI01-09

AOI01-03

AOI02-01

AOI02-02

AOI02-03

LEX-MW002

AOI02-04

LEX-MW004

AOI04-01

AOI02-07

AOI02-06

AOI02-05

AOI01-10

­ Figure 6-3

CLIENT

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Site Inspection at Lexington AASF #1, OK

9/21/2022

9/21/2022

9/21/2022

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

9/21/2022

1:5,400

PFBS Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

Legend

Facility Boundary

Groundwater Flow Direction

LEX-MW005

LEX-MW003

LEX-MW001

LEX-MW002

LEX-MW004

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

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

0 225 450 900

Feet

Shallow Intermediate Deep

PFBS Results (μg/Kg)

ND

>ND - 10

>10 - 1,900

>1,900 - 25,000

>25,000

AECOM 6-17
LEX-MW005

LEX-MW003

LEX-MW001

LEX-MW002

LEX-MW004

AOI01-04

AOI01-05

LEX-MW005

AOI03-01

LEX-MW003

AOI01-01

LEX-MW001

AOI01-02

AOI01-06 AOI01-07

AOI01-08 AOI01-09

AOI01-03

AOI02-01

AOI02-02

AOI02-03

LEX-MW002

AOI02-04

LEX-MW004

AOI04-01

AOI02-07

AOI02-06

AOI02-05

AOI01-10

­ Figure 6-4

CLIENT

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SCALE

PROJECT

ARNG

Site Inspection at Lexington AASF #1, OK

9/21/2022

9/21/2022

9/21/2022

MS

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

9/21/2022

1:5,400

PFHxS Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

Legend

Facility Boundary

Groundwater Flow Direction

LEX-MW005

LEX-MW003

LEX-MW001

LEX-MW002

LEX-MW004

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

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

0 225 450 900

Feet

Shallow Intermediate Deep

PFHxS Results (μg/Kg)

ND

>ND - 10

>10 - 130

>130 - 1,600

>1,600

AECOM 6-18
LEX-MW005

LEX-MW003

LEX-MW001

LEX-MW002

LEX-MW004

AOI01-04

AOI01-05

LEX-MW005

AOI03-01

LEX-MW003

AOI01-01

LEX-MW001

AOI01-02

AOI01-06 AOI01-07

AOI01-08 AOI01-09

AOI01-03

AOI02-01

AOI02-02

AOI02-03

LEX-MW002

AOI02-04

LEX-MW004

AOI04-01

AOI02-07

AOI02-06

AOI02-05

AOI01-10

­ Figure 6-5

CLIENT

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PROJECT

ARNG

Site Inspection at Lexington AASF #1, OK

11/4/2022

11/4/2022

11/4/2022

MS

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

11/4/2022

1:5,400

PFNA Detections in Soil

12420 Milestone Center Drive

Germantown, MD 20876

Legend

Facility Boundary

Groundwater Flow Direction

LEX-MW005

LEX-MW003

LEX-MW001

LEX-MW002

LEX-MW004

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

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

0 225 450 900

Feet

Shallow Intermediate Deep

PFNA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

AECOM 6-19
LEX-MW005

LEX-MW003

LEX-MW001

LEX-MW002

LEX-MW004

LEX-MW005

LEX-MW003

LEX-MW001

LEX-MW002

LEX-MW004

­ Figure 6-6

CLIENT

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PROJECT

ARNG

Site Inspection at Lexington AASF #1, OK

10/6/2022

10/6/2022

10/6/2022

MS

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

10/6/2022

1:5,400

PFOA, PFOS, and PFBS Detections in Groundwater

12420 Milestone Center Drive

Germantown, MD 20876

Legend

Facility Boundary

Groundwater Flow Direction

LEX-MW005

LEX-MW003

LEX-MW001

LEX-MW002

LEX-MW004

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

0 225 450 900

Feet

PFOA PFOS PFBS

PFOA Results (ng/L)

ND

>ND - 6

>6 - 40

>40 - 70

>70

PFOS Results (ng/L)

ND

>ND - 4

>4 - 40

>40 - 70

>70

PFBS Results (ng/L)

ND

>ND - 100

>100 - 601

>601 - 2,000

>2,000

AECOM 6-20
LEX-MW005

LEX-MW003

LEX-MW001

LEX-MW002

LEX-MW004

LEX-MW005

LEX-MW003

LEX-MW001

LEX-MW002

LEX-MW004

­ Figure 6-7

CLIENT

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SCALE

PROJECT

ARNG

Site Inspection at Lexington AASF #1, OK

9/22/2022

9/22/2022

9/22/2022

MS

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GIS BY

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

9/22/2022

1:4,200

PFHxS and PFNA Detections in Groundwater

12420 Milestone Center Drive

Germantown, MD 20876

Legend

Facility Boundary

Groundwater Flow Direction

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

0 175 350 700

Feet

PFHxS PFNA

PFHxS Results (ng/L)

ND

>ND - 39

>39 - 100

>100 - 1,000

>1,000

PFNA Results (ng/L)

ND

>ND - 6

>6 - 100

>100 - 1,000

>1,000

AECOM 6-21
AOI02-08

AOI02-09

AOI02-08

AOI02-09

­ Figure 6-8

CLIENT

REVISED

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ARNG

Site Inspection at Lexington AASF #1, OK

10/6/2022

10/6/2022

10/6/2022

MS

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

10/6/2022

1:5,400

PFOA, PFOS, and PFBS Detections in Surface Water

12420 Milestone Center Drive

Germantown, MD 20876

Legend

Facility Boundary

Surface Water Flow Direction

AOI02-08

AOI02-09

0 225 450 900

Feet

PFOA PFOS PFBS

PFOA Results (ng/L)

ND

>ND - 6

>6 - 40

>40 - 70

>70

PFOS Results (ng/L)

ND

>ND - 4

>4 - 40

>40 - 70

>70

PFBS Results (ng/L)

ND

>ND - 100

>100 - 601

>601 - 2,000

>2,000

AECOM 6-22
AOI02-08

AOI02-09

AOI02-08

AOI02-09

­ Figure 6-9

CLIENT

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ARNG

Site Inspection at Lexington AASF #1, OK

9/22/2022

9/22/2022

9/22/2022

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

9/22/2022

1:4,200

PFHxS and PFNA Detections in Surface Water

12420 Milestone Center Drive

Germantown, MD 20876

Legend

Facility Boundary

Surface Water Flow Direction

0 175 350 700

Feet

PFHxS PFNA

PFHxS Results (ng/L)

ND

>ND - 39

>39 - 100

>100 - 1,000

>1,000

PFNA Results (ng/L)

ND

>ND - 6

>6 - 100

>100 - 1,000

>1,000

AECOM 6-23
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

THIS PAGE INTENTIONALLY BLANK

AECOM 6-24
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

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 7-4. Please note that while the CSM discussion assists in determining if a receptor may 

be impacted, the decision to move from SI to 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, 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, AOI 2, AOI 3, and AOI 4 based on the 

aforementioned criteria. 

7.1.1 AOI 1

At AOI 1, fire training activities were conducted at the Flight Line and nearby Burn Pit sometime 

between the mid to late 1980s to as late as 2008. Releases at AOI 1 have occurred on both paved 

areas and grassy surfaces. Some AFFF releases may have occurred directly onto surface soil 

but may also have infiltrated to the subsurface soil via cracks in pavement or joints between areas 
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 7-2

that are paved with different materials. Surface water flows overland primarily to drainages along 

the western side of the AASF #1 and into the unnamed tributary of Buckhead Creek.

PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in surface soil at AOI 1, at concentrations 

below the SLs. No ongoing construction was observed at the facility during the SI. Site workers 

and future construction workers could contact constituents in surface soil via incidental ingestion 

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

construction workers are potentially complete. The facility is gated, and there are no immediately 

adjacent residential structures; however, the Lexington Wildlife Management area is located just 

north of the Burn Pit. Therefore, the incidental ingestion and inhalation of dust exposure pathways 

for the trespasser and residential receptors are considered incomplete but are potentially 

complete for the recreational user. Shallow subsurface soil was not sampled at AOI 1; however, 

in deep subsurface soil, PFOA, PFOS, PFHxS, and PFNA were detected. The construction worker 

exposure scenario assumes excavation occurs at depths at or above 15 feet bgs. Based on the 

compounds detected in the surface soil and deep subsurface soil, it can be conservatively 

assumed that these compounds would be encountered in the shallow subsurface soil. Therefore, 

construction workers could contact constituents in subsurface soil via incidental ingestion, and 

the subsurface soil exposure pathway for future construction workers is potentially complete. The 

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

7.1.2 AOI 2 

At AOI 2, the Old Fire Station housed two firetrucks from before 1987 to 2006/2007. Once a year, 

nozzle testing occurred at the Old Wash Rack from 1986 to 2004. One reported fire training activity 

was conducted at the Grassy Area Behind Hangar 1; however, the date of the training event is 

unknown. Hangar 2, constructed in 1999-2000, houses a fire suppression system equipped with 

two AFFF 800-gallon tanks and two 36-gallon AFFF tanks. In September 2013, the bladder in one 

of the 800-gallon tanks leaked. The Lagoons are downslope of the Grassy Area Behind Hangar 

1, Hangar 2, Old Fire Station, Old Wash Rack, and the Storage Building; however, berms around 

the Lagoons prevent any stormwater runoff from entering them. The Lagoons received discharge 

from the Old Wash Rack until 2004. Releases at AOI 2 have occurred on both paved areas and 

grassy surfaces. Some AFFF releases may have occurred directly onto surface soil but may also 

have infiltrated to the subsurface soil via cracks in pavement or joints between areas that are 

paved with different materials.

PFOA, PFOS, PFHxS, and PFNA were detected in surface and subsurface soil at AOI 2. 

Additionally, PFOS exceeded the residential SL. Site workers and future construction workers

could contact constituents in surface soil via incidental ingestion and inhalation of dust. Therefore, 

the surface soil exposure pathways for site workers and future construction workers are potentially 

complete. The incidental ingestion and inhalation of dust exposure pathways for the trespasser

and residential receptors are considered incomplete for the same reasons established for AOI 1. 

The recreational user is also considered incomplete at AOI 2 due to the distance to the Lexington 

Wildlife Management Area. Construction workers could contact constituents in subsurface soil via 

incidental ingestion; therefore, the subsurface soil exposure pathway for future construction 

workers is potentially complete. The CSM for AOI 2 is presented on Figure 7-2. 

7.1.3 AOI 3 

AOI 3 is a Mobile Refueler Parking Area where at least one Tri-MaxTM 30 extinguisher was 

historically stored at AOI 3 inside the secondary containment structure. No known or recorded 

leaks or spills occurred at AOI 3; however, any AFFF releases inside the parking area would flow 

to an OWS and flow toward the fence on the eastern side of the facility. Any AFFF release outside 

of the parking area would flow north-northwest, off the pavement, and potentially impact soil.

Surface water at AOI 3 flows west toward the unnamed tributary of Buckhead Creek.
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 7-3

PFOA, PFOS, PFHxS, and PFNA were detected in surface soil at AOI 3. Additionally, PFOS 

exceeded the residential SL. Site workers and future construction workers could contact 

constituents in surface soil via incidental ingestion and inhalation of dust. Therefore, the surface 

soil exposure pathway for site workers and future construction workers are potentially complete

with exceedance of SL. The incidental ingestion and inhalation of dust exposure pathways for the 

trespasser, residential, and recreational user receptors are considered incomplete for the same 

reasons established for AOI 2. The subsurface soil was not sampled at AOI 3; therefore, the 

pathways for subsurface soil ingestion for all receptors cannot be directly evaluated but could be 

conservatively considered to be similar to AOI 1 and AOI 2 due to the presence of relevant 

compounds in surface soil. The CSM for AOI 3 is presented on Figure 7-3. 

7.1.4 AOI 4

AOI 4 is the Fuel Point where two Tri-MaxTM 30 extinguishers were historically stored. No leaks 

or spills were recorded or noted by interviewees. AOI 4 has a concrete surface with two storm 

drains. AFFF releases would drain to the OWS. The OWS and storm drains channel water 

northward to a surface discharge, which then drains overland to a pond and unnamed tributary of 

Buckhead Creek.

PFOA, PFOS, PFHxS, and PFNA were detected in surface soil at AOI 4, 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 surface soil exposure pathway for 

site workers and future construction workers are potentially complete. The incidental ingestion 

and inhalation of dust exposure pathways for the trespasser, residential, and recreational user 

receptors are considered incomplete for the same reasons established for AOI 2 and AOI 3. The 

subsurface soil was not sampled at AOI 4; therefore, the pathways for subsurface soil ingestion 

for all receptors cannot be directly evaluated but could be conservatively considered to be similar 

to AOI 1 and AOI 2 due to the presence of relevant compounds in surface soil. The CSM for AOI 

4 is presented on Figure 7-4. 

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. Drinking 

water at the facility is supplied by a well located on the adjacent Oklahoma Department of 

Corrections facility to the east. Numerous domestic, agricultural, and public supply wells were 

located within a 2-mile radius of the facility. Downgradient public supply wells within a 2-mile 

radius of the facility were not identified; however, a well designated as domestic use was identified

on the property located immediately south of AASF #1 (Oklahoma Water Resources Board, 2021). 

7.2.1 AOI 1

PFOA, PFOS PFBS, PFHxS, and PFNA were detected in groundwater at AOI 1; PFOS was 

measured at a concentration above the SL. 

The facility water supply well is located approximately 2,800 feet east-southeast and side-gradient 

from the well sampled at AOI 1. Additionally, decontamination water source samples collected 

from the facility’s potable water had detections of relevant compounds below their SLs. Therefore, 

the pathway for exposure to site workers via ingestion of groundwater is considered potentially 

complete, but it is incomplete for trespassers because the facility is secure. Due to the presence 

of downgradient wells within 2 miles of the facility, with total depths as shallow as 65 feet bgs, the 

pathway for exposure to off-facility residents via ingestion of groundwater is considered potentially 

complete. Depth to water measured at AOI 1 in April 2022 during the SI was 38.57 feet bgs. The 

construction worker exposure scenario assumes excavation occurs at depths at or above 15 feet 
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 7-4

bgs. Based on the depth to groundwater at AOI 1, the incidental ingestion exposure pathway for 

future construction workers is considered incomplete. The CSM for AOI 1 is presented on Figure 

7-1. 

7.2.2 AOI 2 

PFOA, PFOS PFBS, PFHxS, and PFNA were detected in groundwater at AOI 2; PFOA, PFOS, 

and PFHxS were measured at concentrations above their SLs. 

The facility water supply well is located approximately 800 feet east-southeast and side-gradient 

from AOI 2. Therefore, the pathway for exposure to site workers via ingestion of groundwater is 

considered potentially complete. The ingestion of groundwater exposure pathways for the 

residential receptors are considered potentially complete and incomplete for trespassers, for the 

same reasons established for AOI 1. Depths to water measured during the SI in April 2022 were 

as shallow as 12.75 feet bgs; therefore, the incidental ingestion exposure pathway for future 

construction workers is considered potentially complete. The CSM for AOI 2 is presented on 

Figure 7-2. 

7.2.3 AOI 3 

Groundwater samples were not collected at AOI 3. Groundwater was not sampled at this AOI; 

therefore, the groundwater exposure pathway cannot be directly evaluated, but it is conservatively 

considered similar to AOI 1 and AOI 2 based on the detections of relevant compounds in surface 

soil and the groundwater flow direction; therefore, the ingestion of groundwater exposure pathway

for site workers and residential receptors is potentially complete. The CSM for AOI 3 is presented 

on Figure 7-3. 

7.2.4 AOI 4

Groundwater samples were not collected at AOI 4. Since groundwater was not sampled at this 

AOI, the groundwater exposure pathway cannot be directly evaluated. There were no 

exceedances in surface soil at AOI 4 as at AOI 3, and uncertainty in groundwater flow in this part 

of the facility; therefore, the ingestion of groundwater exposure pathway for all receptors is 

considered incomplete. The CSM for AOI 4 is presented on Figure 7-4. 

7.3 Surface Water and Sediment Exposure Pathway

The SI results in surface water and sediment were used to determine whether a potentially 

complete pathway exists between the source and potential receptors at each AOI based on the 

aforementioned criteria. Surface water samples were only collected at AOI 2. At AOIs where 

surface water and/or sediment samples were not collected, the SI results in soil and groundwater, 

in combination with knowledge of the fate and transport properties of PFAS, were used to 

determine whether a potentially complete pathway exists between the source and potential 

receptors. 

7.3.1 AOI 1

PFAS are water soluble and can migrate readily from soil to surface water via leaching and runoff. Because PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in soil and groundwater at 

AOI 1, it is possible that these compounds may have migrated from soil and groundwater to the 

tributaries to the west. The tributaries then flow into Buckhead Creek and then southwest into the 

Canadian River. Based on the recreational use of the Canadian River, the surface water and 

sediment ingestion exposure pathways for off-facility recreational users are considered potentially 

complete. Surface water is not used as drinking water in the vicinity, so the surface water ingestion 
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 7-5

pathway for residential receptors is incomplete. Due to the presence of constructed drainage 

ditches/pathways at the facility, the surface water and sediment ingestion exposure pathway for 

site workers and future construction workers is considered potentially complete. The CSM for AOI 

1 is presented on Figure 7-1. 

7.3.2 AOI 2 

PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in surface water samples collected in the 

Lagoons. Wastewater in the Lagoons does not discharge to any other surface water body and is 

designed to evaporate. However, the liners were noted to be torn in a number of places during 

the PA and, during the SI, the dike was observed to be leaking to the lowland area southeast of 

the lagoons. Additionally, PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in soil and 

groundwater at AOI 2. The surface water and sediment exposure pathways for off-facility 

recreational user receptors are considered potentially complete for the same reasons established 

for AOI 1. The ingestion of surface water exposure pathways for the off-facility residential 

receptors are considered incomplete for the same reasons established for AOI 1. Due to the 

presence of constructed drainage ditches/pathways at the facility, as well as the Lagoons from 

which the surface water was sampled, the surface water and sediment ingestion exposure 

pathway for site workers and future construction workers is considered potentially complete. The 

CSM is presented on Figure 7-2. 

7.3.3 AOI 3 and AOI 4 

PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in surface soil at AOI 3 and AOI 4. 

Subsurface soil and groundwater were not sampled at these AOIs during the SI. It is possible that 

those compounds may have migrated from surface soil via runoff to the tributaries to the west, 

and subsequently to Buckhead Creek and Canadian River. The surface water and sediment 

exposure pathways for off-facility recreational user, site worker, and future construction worker 

receptors are considered potentially complete for the same reasons established for AOI 1 and 

AOI 2, and they are considered incomplete for off-facility residential receptors. The CSM for AOI 

3 is presented on Figure 7-3, and the CSM for AOI 4 is presented on Figure 7-4. 
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 7-6

THIS PAGE INTENTIONALLY BLANK
Media

SOURCE PATHWAY R

AOI 1

AFFF 

Discharge 

During Fire 

Training 

Activities

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

Lexington AASF #1, Lex

Surface 

Water

Surface 

Water Flow

NOTES1. The resident and recreational users referto off-site receptors.2. Construction was not observed during SIfield activities.

Surface Soil

/ 

Site 

Worker

Con

W

Site 

Worker

Con

W

/ 

/ 

/ 

Potential 

Off-Facility 

Source Not 

Under 

Control of 

ARNG

/ 
Media

SOURCE PATHWAY R

AOI 2

AFFF Fire 

Suppression 

System, AFFFEquipped 

Firetruck Storage/

Washing, AFFF 

Discharge, and 

AFFF Storage

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

Lexington AASF #1, Lex

Surface 

Water

Surface 

Water Flow

NOTES1. The resident and recreational users referto off-site receptors.2. Construction was not observed during SIfield activities.

Surface Soil

/ 

Site 

Worker

Con

W

Site 

Worker

Con

W

/ 

Potential 

Off-Facility 

Source Not 

Under 

Control of 

ARNG

/ / / 
Media

SOURCE PATHWAY

AOI 3 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

Flow-Chart ContinuesPartial / Possible FlowFlow-Chart StopsIncomplete PathwayPotentially Complete PathwayPotentially Complete Pathway with Exceedance of SL

LEGEND

Figure 7

Conceptual Site M

Lexington AASF #1, Lex

Surface 

Water

Surface 

Water Flow

NOTES1. The resident and recreational users referto off-site receptors2. Subsurface soil and groundwater was notsampled at AOI 3.3. Construction was not observed during SIfield activities.

/ 

Site 

Worker

Con

W

Site 

Worker

Con

W

/ 

RHu

C

Potential 

Off-Facility 

Source Not 

Under 

Control of 

ARNG

/ / / 
Media

SOURCE PATHWAY R

AOI 4 AFFF Storage

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

Lexington AASF #1, Lex

Surface 

Water

Surface 

Water Flow

NOTES1. The resident and recreational users referto off-site receptors.2. Subsurface soil and groundwater was notsampled at AOI 4.3. Construction was not observed during SIfield activities.

Surface Soil

/ 

Site 

Worker

Con

W

Site 

Worker

Con

W

/ / 

/ 

/ 

Potential 

Off-Facility 

Source Not 

Under 

Control of 

ARNG
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

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 6 to 22 April 2022 and consisted of utility clearance, 

sonic drilling, soil sample collection, permanent monitoring well installation, low-flow groundwater 

sample collection, surface water sample collection, and land surveying. Field activities were 

conducted in accordance with the SI QAPP Addendum (AECOM, 2021), except as previously noted 

in Section 5.9. 

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

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

Table B-15 as follows. 

• Thirty-four (34) soil samples from 24 locations; 

• Five (5) low-flow groundwater samples from 5 permanent monitoring wells; 

• Two (2) surface water samples from 2 surface water locations; and

• Twenty-two (22) 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: Northern Release 

Areas, AOI 2: Eastern Release Areas, and AOI 3: Mobile Refueler Parking Area. No further 

evaluation is warranted for AOI 4: Fuel Point at this time. Based on the CSMs developed and 

revised in light of the SI findings, there is potential for exposure to drinking water receptors 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, PFBS, PFHxS, and PFNA in soil at 

AOI 1 were below their SLs. 

• PFOS in groundwater exceeded the 4 ng/L SL, at a concentration of 7.93 ng/L at 

LEX-MW001. PFOA, PFBS, PFHxS, and PFNA were detected in groundwater, below 

their SLs.

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

Lexington AASF #1, Lexington, Oklahoma

AECOM 8-2

• At AOI 2: 

• PFOS exceeded the 13 μg/kg SL in surface soil, at a maximum concentration of 22.8 

μg/kg at LEX-MW003. The detected concentrations of PFOA, PFBS, PFHxS, and 

PFNA in soil at AOI 2 were below their SLs. 

• In groundwater, PFOA exceeded the 6 ng/L SL, with a maximum concentration of 

804 ng/L. PFOS exceeded the 4 ng/L SL, with a maximum concentration of 18.8 ng/L. 

PFHxS exceeded the 39 ng/L SL, with a maximum concentration of 4,220 ng/L. The 

maximum concentrations were all detected at LEX-MW003. PFBS and PFNA were 

detected in groundwater below their SLs at AOI 2.

• PFOA, PFOS, PFBS, PFHxS, and PFNA were detected in surface water. The 

maximum concentration detected was PFHxS, at 231 ng/L at AOI02-09. 

• Based on the results of the SI, further evaluation of AOI 2 is warranted in an RI.

• At AOI 3: 

• PFOS exceeded the 13 μg/kg SL in surface soil, at a concentration of 18.5 μg/kg at 

AOI03-01. PFOA, PFHxS, and PFNA were detected at concentrations at least two

orders of magnitude below their SLs, and PFBS was not detected. Subsurface soil 

was not sampled.

• Groundwater was not sampled at AOI 3.

• Based on the results of the SI, further evaluation of AOI 3 is warranted in an RI.

• At AOI 4:

• The detected concentrations of PFOA, PFOS, PFHxS, and PFNA in soil at AOI 4 

were below their SLs. PFBS was not detected. Subsurface soil was not sampled.

• Groundwater was not sampled at AOI 4.

• Based on the results of the SI, further evaluation of AOI 4 is not warranted at this 

time. 

Groundwater in the vicinity of the facility was anticipated to flow south. Based on the results of 

the SI, local groundwater at the facility flows southwest. The shallowest depths to groundwater 

were observed at AOI 2 in the vicinity of the Lagoons.

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. 
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 8-3

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

AOI Potential 

Release Area

Soil – 

Source Area

Groundwater – 

Source Area

Groundwater –

Facility 

Boundary

Future Action

1 Northern Release 

Areas N/A Proceed to RI 

2 Eastern Release 

Areas Proceed to RI

3 Mobile Refueler 

Parking Area N/A N/A Proceed to RI

4 Fuel Point N/A N/A No further 

action

Legend:

N/A = not applicable

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels
Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 8-4

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Site Inspection Report

Lexington AASF #1, Lexington, Oklahoma

AECOM 9-1

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W912DR17F0192. 9 March.

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Contract No. W912DR-12-D-0014/W912DR17F0192. July.

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Acid (PFOS) and Perfluorooctanoic Acid (PFOA) Impacted Sites ARNG Installations, 

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AECOM 9-2

Mashburn, S.L, Ryter, D.W., Neel, C.R., Smith, S.J., and Correll, J.S. 2019. Hydrogeology and 

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