FINAL

Site Inspection Report 

Buckley Army Aviation Support Facility

Aurora, Colorado

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 

September 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........................................................................................................2-4

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

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 Building 1510 ..............................................................................................3-1

3.2 AOI 2 Former Tri-MaxTM Storage Area...................................................................3-1

3.3 Adjacent Sources ..................................................................................................3-2

3.3.1 Buckley Space Force Base .........................................................................3-2

3.3.2 City of Aurora Fire Stations .........................................................................3-3

3.3.3 Site 3 – Former Base Landfill ......................................................................3-3

3.3.4 Waste Water Treatment Plants....................................................................3-4

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

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

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

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

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

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

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

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

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

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

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

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

5.3 Permanent Well Installation and Groundwater Sampling.......................................5-3

5.4 Synoptic Water Level Measurements ....................................................................5-4

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

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

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

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

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

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

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

6.3 AOI 1.....................................................................................................................6-2
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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 Conclusions ......................................................................................6-4

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

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

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

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

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

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

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

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

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. Field Change Request Form

B4. Nonconformance and Corrective Action Report

B5. 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, July 2022

Figure 2-5 Surface Water Features

Figure 3-1 Areas of Interest

Figure 5-1 Site Inspection Sample Locations

Figure 6-1 PFOA Detections in Soil

Figure 6-2 PFOS Detections in Soil

Figure 6-3 PFBS Detections in Soil

Figure 6-4 PFHxS Detections in Soil

Figure 6-5 PFNA Detections in Soil

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

Figure 6-7 PFHxS and PFNA Detections in Groundwater

Figure 7-1 Conceptual Site Model, AOI 1

Figure 7-2 Conceptual Site Model, AOI 2

Tables

Table ES-1 Screening Levels (Soil and Groundwater)

Table ES-2 Summary of Site Inspection Findings and Recommendations

Table 5-1 Site Inspection Samples by Medium

Table 5-2 Soil Boring Depths and Permanent Well Screen Intervals

Table 5-3 Permanent Monitoring Well Screen Intervals and Groundwater Elevations

Table 6-1 Screening Levels (Soil and Groundwater)

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

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

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

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

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

% percent

°C degrees Celsius

°F degrees Fahrenheit

μg/kg micrograms per kilogram

μg/L micrograms per liter

AASF Army Aviation Support Facility

AECOM AECOM Technical Services, Inc.

AFB Air Force Base

AFFF aqueous film-forming foam

amsl above mean sea level

ANG Air National Guard

AOI Area of Interest

ARNG Army National Guard

ASTM American Society for Testing and Materials

bgs below ground surface 

CDPHE Colorado Department of Public Health and Environment

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act 

COARNG Colorado Army National Guard

CoC chain of custody

CSM conceptual site model

DA Department of the Army

DoD Department of Defense

DOT Department of Transportation

DQO data quality objective

DUA data usability assessment

ELAP Environmental Laboratory Accreditation Program

EM Engineer Manual

FedEx Federal Express

FEMA Federal Emergency Management Agency

FTA Fire Training Area

GPRS Ground Penetrating Radar Systems

GSE Ground Services Equipment

HA Health Advisory

HDPE high-density polyethylene 

HEF High Expansion Foam

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

MS matrix spike

MSD matrix spike duplicate

NAD83 North American Datum 1983
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NELAP National Environmental Laboratory Accreditation Program

NOAA National Oceanic and Atmospheric Administration

ng/L nanograms per liter

OSD Office of the Secretary of Defense

OWS oil-water separator

PA Preliminary Assessment 

PFAS per- and polyfluoroalkyl substances

PFBS perfluorobutanesulfonic acid

PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

PID photoionization detector

PQAPP Programmatic UFP-QAPP

PVC polyvinyl chloride

QA quality assurance 

QAPP Quality Assurance Project Plan

QC quality control

QSM Quality Systems Manual

RI Remedial Investigation

ROD Record of Decision

SACWSD South Adams County Water and Sanitation District

SFB Space Force Base

SI Site Inspection 

SL screening level

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

WWTP wastewater treatment plant
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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 6 July 2022 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 two 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 screening 

levels (SLs) for relevant compounds. This SI was completed at the Buckley Army Aviation 

Support Facility (AASF) in Aurora, Colorado and determined further evaluation under the 

Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) is 

warranted for AOI 1 and AOI 2. The Buckley AASF will also be referred to as the “facility” 

throughout this document. 

The Buckley AASF is a tenant of the Buckley Space Force Base (SFB) located in Aurora, 

Colorado. The facility is located west of the Buckley SFB runway and includes hangar space for 

aircraft maintenance and storage, office and administrative buildings, a readiness center, a flight 

ramp, a helipad, and a taxiway connecting the facility flight ramp to the Buckley SFB runway. An 

additional joint-use building shared by the Colorado ARNG (COARNG) and Buckley SFB that is 

predominantly used by Buckley SFB is located on a flight ramp approximately 0.5 miles north of 

the COARNG Buckley AASF complex. The larger Buckley SFB property, which is zoned entirely 

for Buckley SFB use, encompasses 3,540 acres. The COARNG Buckley AASF is leased from 

the Buckley SFB (AECOM Technical Services, Inc. [AECOM], 2021).

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

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

Based on the results of the SI, particularly the detections in groundwater at BKLY-MW003, there 

is evidence of contaminated groundwater entering the facility at the upgradient boundary that is 

not attributable to ARNG activities. Based on the results of this SI, further evaluation under 

CERCLA is warranted in a Remedial Investigation (RI) for AOI 1 and AOI 2. 

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

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

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

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

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

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

Analyteb

Residential

(Soil)

(μg/kg)a 

0-2 feet bgs

Industrial/ Commercial 

Composite Worker

(Soil)

(μg/kg)a 

2-15 feet bgs

Tap Water

(Groundwater)

(ng/L)a

PFOA 19 250 6

PFOS 13 160 4 

PFBS 1,900 25,000 601 

PFHxS 130 1,600 39

PFNA 19 250 6

Notes:

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

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

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

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

included as an analyte at the time of this SI. Based on the CSM developed during the PA and revised based on SI findings, the presence 

of 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 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 Building 1510 NS Proceed to 

RI 

2 Former Tri-MaxTM 

Storage Area NS Proceed to RI

Legend:

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected

NS = not sampled
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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 perand 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 6 July 2022 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 (HFPODA)1

, and perfluorobutanesulfonic acid (PFBS) at ARNG facilities nationwide. The ARNG 

performed this SI at the Buckley Army Aviation Support Facility (AASF) in Aurora, Colorado. The 

Buckley AASF is also referred to as the “facility” throughout this document. 

The SI project elements were performed in compliance with Comprehensive Environmental 

Response, Compensation, and Liability Act (CERCLA; United States [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 Buckley AASF (AECOM Technical Services, Inc. [AECOM], 2021) that

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

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

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

further investigation is warranted, a removal action is required to address immediate threats, or 

no further action is required based on screening levels (SLs) for the relevant compounds. 

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

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

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

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

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

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

2.1 Facility Location and Description

The Buckley AASF is a tenant of the Buckley Space Force Base (SFB) located in Aurora, 

Colorado (Figure 2-1). The Colorado ARNG (COARNG) has maintained a presence at Buckley 

SFB since 1977, when Building 1500 was constructed to be the facility hangar. Since 1977, the 

facility has been improved with numerous buildings and developments, with the most recent 

being the construction of Building 1510, a new facility main hangar. Buckley AASF is designed 

to house, equip, support, and maintain military aircraft. The facility is located west of the Buckley 

SFB runway and includes hangar space for aircraft maintenance and storage, office and 

administrative buildings, a readiness center, a flight ramp, a helipad, and a taxiway connecting 

the facility flight ramp to the Buckley SFB runway. An additional joint-use building shared by the 

COARNG and Buckley SFB is located on a flight ramp predominantly used by Buckley SFB, 

located approximately 0.5 miles north of the COARNG Buckley AASF complex. The larger 

Buckley SFB property, which is zoned entirely for Buckley SFB use, encompasses 3,540 acres. 

The COARNG Buckley AASF is leased from the Buckley SFB. 

The DA opened Buckley Field in 1942 to train the Army Air Corps, and they transferred the field 

to the Department of the Navy in 1945. The Navy deactivated the facility in 1959, and operation 

of the facility transferred to the State of Colorado as Buckley Air National Guard (ANG) Base. 

Buckley ANG Base was used for military aviation and support activities for the Colorado ANG. 

The base was reassigned from the ANG to the Air Force Space Command and renamed 

Buckley Air Force Base in 2001. In 2021, Buckley Air Force Base was renamed Buckley Space 

Force Base.

2.2 Facility Environmental Setting

Buckley SFB is situated on high ground dividing the Sand Creek and Toll Gate Creek drainage 

basins. The ground surface elevation of Buckley SFB ranges from 5,700 feet above mean sea 

level (amsl) at the southeast corner to 5,480 feet amsl at the northwest corner. The COARNG 

Buckley AASF is situated at approximately 5,585 feet amsl, towards the center of the SFB

property (USEPA, 2019) (Figure 2-2). A new building to the southeast of Building 1510 was 

observed to be under construction during the time of the site investigation. 

Most of the operational portions of Buckley AASF facility are paved with asphalt or concrete. 

Scrub vegetated areas surround the improved portions of the facility, particularly to the north, 

south, and east. The facility is bounded on the north, west, and south sides by a chain-link 

fence; the eastern boundary of the property is open to the greater Buckley SFB area. Buckley 

SFB is a fenced facility and access is through a security check point. According to facility 

personnel, Buckley AASF is provided drinking water by the City of Aurora, and sanitary sewers 

connect the facility to the Denver Metro Wastewater Reclamation District.

2.2.1 Geology

Buckley AASF is located within the Denver Basin, a shallow, bowl-shaped basin covering an 

area of approximately 6,700 square miles. The basin is filled with sedimentary rocks formed by 

deposition resulting from the uplift and erosion of the Rocky Mountains to the west.

These sedimentary deposits are comprised of six geologic formations, which follow in 

descending order: the Castle Rock Conglomerate, the Dawson Arkose, the Denver, Arapahoe, 

and Laramie formations, and the Fox Hills Sandstone. The Cretaceous Pierre Shale Formation, 

consisting primarily of relatively impermeable shale, is located beneath the Fox Hills Sandstone 
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within the Denver Basin. Of the six geologic formations found in the Denver Basin, only the 

Denver, Arapahoe, and Laramie formations and the Fox Hills Sandstone are found under the 

larger Buckley SFB property (USEPA, 2019).

The majority of the Denver Formation is composed of approximately 70 percent (%) shale and 

claystone, with the remaining materials composed of coarse-grained sediments irregularly 

dispersed in lenticular beds. Under Buckley SFB, the Denver Formation is approximately 850 

feet thick and crops out in the northeastern, eastern, and southwestern parts of the base, 

including beneath much of the AASF (USEPA, 2014). Where the Denver Formation is not 

present at the surface, it is often covered with a thin mantle of aeolian (windblown) deposits of 

loess and fine sand that are generally less than 10 feet thick. Additionally, alluvial deposits from 

the erosion of the Denver Formation are present along the valleys of the Sand and Toll Gate 

creeks and their tributaries, as well as in buried paleochannels (USEPA, 2019). A 2019 Record 

of Decision (ROD) for a property within the Buckley SFB encountered alluvial, and possibly 

aeolian, soils from ground surface to approximately 12 feet below ground surface (bgs). Below 

the alluvium is predominately the weathered claystone and siltstone of the Denver Formation, 

with minor weathered, interbedded sandstone (USEPA, 2019). Local geologic units are shown 

on Figure 2-3. 

During the SI, sands and low to medium plasticity fines (silts with clay) were observed as the 

dominant lithology of the unconsolidated sediments below the Buckley AASF. The borings were 

terminated at depths between 45 and 57.5 feet bgs, with the bottom of the wells set between 40

and 51.5 feet bgs. The sands were described as poorly graded, with intervals of silty clay and 

silty sands with varying percentages of gravel observed in each of the borings. A sample for 

grain size analyses was collected at BKLY-MW002 and analyzed via American Society for 

Testing and Materials (ASTM) Method D-422. The results indicate that the soil samples are 

comprised primarily of silt (31.74%) medium sand (28.07%), and clay (20%).These results and 

facility observations are consistent with the reported alluvial and weathered rock deposits at the 

facility. Boring logs are presented in Appendix E and grain size results are presented in 

Appendix F.

2.2.2 Hydrogeology

Groundwater under the greater Buckley SFB area exists within the unconsolidated aeolian and 

alluvial surficial deposits, as well as in the Denver Formation, where it is primarily present in the 

discontinuous layers of coarse-grained materials (sand and sandstones) within the fine-grained 

materials (clay, silt, claystones, and siltstones). Groundwater in the Denver Formation may also 

exist in fractured sections of siltstones and claystones. Generally, unconfined groundwater 

conditions exist in the weathered, upper part of the Denver Formation and overlying surficial 

deposits, whereas semiconfined or confined conditions are present in the deeper portions of the 

Denver Formation, particularly where it is overlain by other bedrock formations. Aquifer recharge 

across Buckley SFB occurs through direct infiltration of precipitation and/or irrigation and 

drainage ditch water. Groundwater discharge occurs primarily through seepage at streams and 

as evapotranspiration where groundwater is present at formation outcrops (USEPA, 2014). The 

Denver, Arapahoe, and Laramie-Fox Hills Aquifers are the three principal bedrock aquifers at 

Buckley SFB (in descending order). Due to the thickness and hydrogeologic conditions of the 

Denver Formation, surficial releases are unlikely to impact the deeper aquifers. The Denver 

Formation is 600 to 1,000-feet thick (Aerostar SES LLC, 2019). 

Regional groundwater flow is generally to the northwest, following the trend of stream drainages 

toward the South Platte River north of Denver (Figure 2-3) (URS, 2007). Groundwater flow 

direction at a former landfill adjacent to the southwest of the facility is towards the westnorthwest and is presumed to be the same at the facility (USEPA, 2014). Water levels collected 
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during an SI conducted by the Air Force at Buckley SFB in 2019, then Buckley Air Force Base 

(AFB), also indicated a northwesterly groundwater flow direction (Aerostar SES LLC, 2019). 

The Denver Basin aquifer system, which includes the Denver, Arapahoe, and Laramie-Fox Hills 

aquifers, is a secondary source of municipal or irrigation water for suburban Denver and 

surrounding rural communities. Unconfined shallow groundwater within the unconfined aquifers 

in and around Buckley AASF is used primarily for irrigation. The City of Aurora, which supplies 

drinking water for Buckley AASF and surrounding residents, draws most of its water from 

surface sources (USEPA, 2019).

The shallow Denver Aquifer groundwater at Buckley AASF is not known to be used as a water 

source for drinking or irrigation for the COARNG or off-site receptors. Numerous wells of various 

use exist in all directions within a 4-mile radius surrounding the facility. In 2018, low levels of

PFAS were detected in water samples collected from shallow wells serving the South Adams 

County Water and Sanitation District's (SACWSD) water supply. The locations of the affected 

wells are unknown; however, the SACWSD treatment facility and service area is within 10 miles 

northwest of Buckley SFB. 

According to the 2014 ROD for the previously mentioned former landfill located approximately 

0.2 miles south of Buckley AASF, depth to groundwater was observed between 40 and 50 feet 

bgs in the southeastern portion of the landfill. Depths to water measured at Buckley AASF in 

July 2022 during the SI ranged from 34.13 to 45.33 feet bgs. Groundwater elevation contours 

from the SI are presented on Figure 2-4 and indicate the groundwater flow direction at the 

AASF is primarily to the northwest.

2.2.3 Hydrology 

Surface water flow across most of the facility follows topography and drains via overland sheet 

flow to the north, to a stormwater retention pond located north of Building 1510 on the northern 

boundary of the COARNG property. The southern portion of the facility flight ramp drains to a 

surface impoundment located east of Building 1515. Three storm drains located across the flight 

ramp connect to underground storm sewer pipes that presumably discharge to the 

aforementioned stormwater retention pond. A fourth storm drain on the flight ramp located 

adjacent to the aircraft wash rack connects to sanitary sewer pipes that continue off-facility. A 

drainage swale on the northeast boundary of the flight ramp flows north and discharges 

overland along the slope located south of the retention pond. A drainage swale adjacent to the 

southern boundary of the flight ramp drains southwest towards the surface impoundment east of 

Building 1515. An oil-water separator (OWS) is located east of Building 1510, at the adjacent 

parking pad, as well as at the southwest corner of the building on the flight ramp (COARNG, 

2017).

A small stream designated as a freshwater emergent wetland by the US Fish and Wildlife 

Service (USFWS) National Wetlands Inventory passes through the eastern and northern 

portions of the SFB, and it ultimately discharges to the East Toll Gate Creek west of the facility 

(USFWS, 2020). The East Toll Gate Creek is located approximately 0.2 miles west of the 

western AASF boundary and flows to the northwest. East Toll Gate Creek confluences with 

Sand Creek approximately 5.5 miles northwest of the facility, and it ultimately discharges to the 

South Platte River further northwest. Lake Williams, a small, occasionally dry reservoir, is also 

located within the greater Buckley SFB, approximately 1 mile northeast of the AASF property 

(USFWS, 2020). However, surface water from the AASF does not drain to the lake. Overflow 

from Lake Williams drains through a series of two unnamed tributaries to Sand Creek (USEPA, 

2019). Surface water features are shown on Figure 2-5. 

Flood Insurance Rate Maps for Arapahoe County identify the entire Buckley SFB as an area of 

minimal flood hazard. The nearest flood zone is associated with the East Toll Gate Creek 
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floodplain and is located approximately 0.2 miles northwest of the facility (Federal Emergency 

Management Agency [FEMA], 2020).

2.2.4 Climate 

Data from the Denver International Airport weather station located approximately 11 miles 

northeast of the Buckley AASF, indicate that the annual average temperature between 2000 and 

2022 was 50.5 degrees Fahrenheit (oF). The warmest months are July and August, with average 

temperatures of 75.6 oF and 73.2 oF, respectively. December is the coldest month, with an 

average temperature of 30.9 oF. Average annual precipitation measured from 2000 to 2022 at 

the airport was 13.18 inches, with the most rain occurring May through July. The average annual 

snowfall from 2000 to 2022 at the airport is 52.6 inches. The majority of snowfall occurs 

between December and March (National Oceanic and Atmospheric Administration [NOAA], 

2022). 

2.2.5 Current and Future Land Use

The Buckley AASF is designed to house, equip, support, and maintain military helicopters for 

the COARNG. Buckley AASF and the area surrounding the larger Buckley SFB complex 

includes industrial and agricultural land to the north, commercial and residential land to the 

west, residential and agricultural land to the south, and agricultural land to the east (USEPA, 

2019). Reasonably anticipated future land use at the AASF and the surrounding area is not 

expected to change from the current land use described above. 

2.2.6 Sensitive Habitat and Threatened/ Endangered Species 

A wildlife survey has not occurred at the facility, and the facility does not have any significant 

areas of habitat. The following species have not been identified at the facility but may be 

present in the surrounding area. 

The following mammals, birds, fishes, insects, and flower plants are federally endangered, 

threatened, proposed, and/ or are listed as candidate species in Arapahoe County, Colorado 

(USFWS, 2022). 

• Mammals: Grey Wolf, Canis lupus (endangered)

• Birds: Piping Plover, Charadrius melodus (threatened); Whooping Crane, Grus americana

(endangered)

• Fishes: Pallid Sturgeon, Scaphirhynchus albus (endangered)

• Insects: Monarch butterfly, Danaus plexippus (candidate)

• Flowering Plants: Ute Ladies'-tresses, Spiranthes diluvialis (threatened); Western Prairie

Fringed Orchid, Platanthera praeclara (threatened)

2.3 History of PFAS Use

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

released historically at the Buckley AASF (AECOM, 2021). PFAS-containing materials may have 

historically been released at the facility during a High Expansion Foam (HEF) system test at 

Building 1510 in 2006 or during outside storage of Tri-MaxTM units prior to 2019. The potential 

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

groundwater flow directions. A description of each AOI is presented in Section 3. 
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Site Inspection Report

Buckley AASF, Aurora, Colorado

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Site Inspection Report

Buckley AASF, Aurora, Colorado

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, two potential release areas were 

identified at Buckley AASF and grouped into two AOIs (AECOM, 2021). The potential release 

areas are shown on Figure 3-1. 

3.1 AOI 1 Building 1510

Building 1510 is the main hangar at Buckley AASF and is located on the north side of the facility 

flight ramp. The building was constructed in 2006 and is designed for the maintenance and 

storage of aircraft. Building 1510 includes 10 bay doors with access to 10 hangars as well as 

office and administrative space on the west end of the building. The eastern portion of the 

building was described during interviews with facility staff as the Ground Services Equipment 

(GSE) building. Building 1510 is constructed with a HEF deluge fire suppression system that 

contains 900 gallons of Ansul Jet-X 2.75% HEF concentrate. A 55-gallon drum containing the 

same HEF concentrate product is also stored within Building 1510. According to facility 

personnel, the HEF deluge fire suppression system was tested in 2006, following its installation. 

The test involved the 3-minute discharge of an unknown volume of Ansul Jet-X 2.75% HEF to 

the hangar area. HEF released during the test was confined to the building interior by the 

building walls and plastic sheeting in front of bay doors. Standing foam was drained via building 

floor drains that connect to sanitary system sewers and ultimately lead to the Denver Metro 

Wastewater Reclamation District system. Typically, floor drains in Building 1510 connect to an 

OWS, but a diverter was used to ensure HEF bypassed the OWS and flowed to sanitary sewers 

that connect to Denver Metropolitan Wastewater Reclamation District facilities. These treatment 

facilities discharge to the South Platte River and transfer biosolids to the Metrogro Farm. The 

Metrogro Farm is used to grow agricultural products and for cattle grazing. 

According to facility staff with knowledge of the test, no HEF is known to have escaped the 

building during the test. Although the HEF system test was described as being confined to the 

building interior, it is possible that HEF was tracked out of the building following the system test 

or during cleanup activities. The HEF product released at Buckley AASF is conservatively 

assumed to have contained PFAS for the purpose of this investigation. If HEF released from the 

deluge system test were tracked outside of the building following the test, it may have migrated 

to the surrounding paved surfaces and/or landscaped areas on the north side of Building 1510. 

Surface water runoff from the paved surfaces around Building 1510 flows towards the retention 

pond north of Building 1510. Surface water runoff from AOI 1 may also enter the small stream in 

the northeastern portion of the facility, which connects to East Toll Gate Creek, Sand Creek, and 

ultimately, the South Platte River.

No other fire suppression system tests involving the release of HEF have occurred at Building 

1510 since its construction, and facility personnel stated that the HEF system room exhibits no 

evidence of corrosion, leakage, or spills. 

3.2 AOI 2 Former Tri-MaxTM Storage Area 

AOI 2 encompasses the area in the northeastern portion of the facility formerly used to store six 

Tri-MaxTM wheeled fire extinguishers containing Chemguard 3% C-303 AFFF concentrate. It is 

unclear how long the Tri-MaxTM units were stored in this location, but they were removed and 

disposed of in a controlled manner in September 2019. Although no known PFAS releases have 

occurred in this area, the outdoor storage of Tri-MaxTM and corrosive nature of AFFF may have 

led to incidental releases.
Site Inspection Report

Buckley AASF, Aurora, Colorado

AECOM 3-2

Potential releases at AOI 2 would most likely have occurred to paved surfaces but may migrate 

a short distance to grassy areas. Surface water runoff from AOI 2 may potentially migrate 

towards the retention pond north of Building 1510. It is also possible that surface water runoff 

from the area may enter the small stream in the northeastern portion of the facility, which 

connects to East Toll Gate Creek, Sand Creek, and ultimately, the South Platte River.

3.3 Adjacent Sources

Multiple off-facility, potential sources were identified adjacent to the Buckley AASF during the PA 

and are not associated with ARNG activities. The adjacent potential sources are shown on 

Figure 3-1 and described in the following sections for informational purposes only and were not 

investigated as part of this SI. 

3.3.1 Buckley Space Force Base 

Fire training and other activities resulting in PFAS-containing material releases have occurred in 

several locations associated with the Buckley SFB. Based on a 2019 SI report for AFFF use at 

Buckley SFB, two fire training areas (FTAs), one hangar, the former fire station, and two crash 

sites were identified as areas where AFFF may have been released to the environment 

(Aerostar SES LLC, 2019). 

The AFFF release areas at Buckley SFB investigated as part of the 2019 SI report include the 

following locations: 

• FTA No. 2 - FTA No. 2 was an unlined burn area for jet fuels and was operational

between 1950 and 1972. FTA No. 2 is located potentially upgradient of Buckley AASF,

approximately 3,200 feet east.

The 2019 SI sample results indicated detections of PFOA, PFOS, and PFBS in soil

with maximum concentrations of 36 J μg/kg, 7,200 μg/kg, and 8,500 J μg/kg,

respectively. PFOA, PFOS, and PFBS were detected in groundwater at maximum

concentrations of 19 μg/L, 190 μg/L, and 90 μg/L, respectively.

• FTA No. 3 - Fire training exercises were performed annually at FTA No. 3 between

1972 and 1989. Jet fuel solutions were ignited and extinguished with AFFF during

training events; approximately 400 gallons of AFFF were used annually. In 2006, a

removal action was performed to remove soil impacted by volatile organic compounds,

and in 2008, the area was paved over to become a parking lot. FTA No. 3 is located

downgradient of Buckley AASF, approximately 4,200 feet northwest.

The 2019 SI sample results indicated detections of PFOA, PFOS, and PFBS in soil

with maximum concentrations of 5.8 μg/kg, 9.5 μg/kg, and 930 μg/kg, respectively.

PFOA, PFOS, and PFBS were detected in groundwater at maximum concentrations of

0.27 μg/L, 0.99 μg/L, and 3.6 μg/L, respectively.

• Hangar 801 - One documented release of approximately 400 gallons of Ansulite 3%

AFFF mixed with 13,000 to 14,000 gallons of water is known to have occurred at

Hangar 801. Approximately 2,000 to 5,000 gallons of the AFFF solution were released

to sanitary sewers and migrated to the surface of a nearby road. AFFF solution also

migrated from the nearby road surface to stormwater sewers. Hangar 801 is located

downgradient of Buckley AASF, approximately 3,200 feet northwest.

The 2019 SI sample results indicated no detections of PFBS in soil. PFOA and PFOS

were detected in soil with maximum concentrations of 0.84 J μg/kg, and 30 μg/kg.

PFBS, PFOA, and PFOS were detected in groundwater at maximum concentrations of

0.23 μg/L, 0.43 μg/L, and 5.9 μg/L, respectively.
Site Inspection Report

Buckley AASF, Aurora, Colorado

AECOM 3-3

• Former Fire Station #2 - AFFF was stored at the former fire station, and annual spray

testing was conducted on an outdoor pad adjacent to the fire station, which resulted in

the release of AFFF. Former Fire Station #2 is located potentially upgradient of Buckley

AASF, approximately 3,100 feet east.

The 2019 SI sample results indicated detections of PFBS, PFOA, and PFOS in soil

with maximum concentrations of 2.0 J μg/kg, 3.4 μg/kg, and 590 μg/kg, respectively.

PFBS, PFOA, and PFOS were detected in groundwater at maximum concentrations of

4.5 μg/L, 6.8 μg/L, and 30 μg/L, respectively.

• F-5 Crash Site - Approximately 100 to 200 gallons of AFFF were sprayed on a fuel spill

resulting from an aircraft crash on the Buckley SFB runway in the late 1980s. The F-5

crash site is located down or cross gradient of Buckley AASF, approximately 2,000 feet

north.

The 2019 SI sample results indicated detections of PFBS, PFOA, and PFOS in soil

with maximum concentrations of 0.33 J μg/kg, 0.49 J μg/kg, and 200 μg/kg,

respectively. PFBS, PFOA, and PFOS were detected in groundwater at maximum

concentrations of 0.097 μg/L, 0.029 μg/L, and 0.044 μg/L, respectively.

• F-16 Crash Site - Approximately 200 gallons of AFFF were sprayed at the location of

an aircraft crash on grass adjacent to the south end of the Buckley SFB runway in

1995. The F-16 crash site is located upgradient of Buckley AASF, approximately 6,300

feet southeast.

The 2019 SI sample results indicated that no PFAS compounds were detected in soil.

In groundwater, PFBS was not detected, and the maximum detected concentrations of

PFOA and PFOS are 0.0094 J μg/L and 0.016 J μg/L, respectively.

3.3.2 City of Aurora Fire Stations 

Numerous fire stations associated with the City of Aurora Fire Department are located 

throughout the City of Aurora. Aurora Fire Station No. 9 and Aurora Fire Station No. 8 are the 

two nearest fire stations to the Buckley AASF that are associated with the City of Aurora Fire 

Department. Fire Station No. 9 is located approximately 1.8 miles southwest and cross gradient 

of the facility, and Fire Station No. 8 is approximately 2.5 miles northwest and downgradient of 

the facility.

It is unknown whether the Aurora Fire Department fire stations store or use AFFF during training 

or emergency response. Given the tendency for local fire departments to store AFFF for 

emergency purposes, it is possible AFFF is stored at these locations. It is also unclear whether 

the fire department performs vehicle maintenance, such as nozzle tests, at the fire stations. Due 

to the likelihood that AFFF has been stored and/or released at the fire stations as a result of 

potential training and maintenance, the City of Aurora Fire Department fire stations are 

considered potential release areas. 

3.3.3 Site 3 – Former Base Landfill

There are no landfills within the footprint of the COARNG property; however, Buckley SFB

Installation Restoration Program Site 3 comprises the Former Base Landfill and is located 

immediately south and cross gradient of the Buckley AASF. Site 3 is a series of former disposal 

areas that were used between 1942 and 1982 for municipal refuse disposal. The general 

method of operation for the Former Base Landfill was to dig a trench, fill the trench with waste 

material, and cover the material with earth. Portions of Site 3 are bisected by East Toll Gate 

Creek (USEPA, 2014). 
Site Inspection Report

Buckley AASF, Aurora, Colorado

AECOM 3-4

Landfills are not usually a primary potential release area of PFAS, but materials disposed of in 

landfills may create a secondary source of contamination. Such materials, to name a few, may 

include sludge from a wastewater treatment plant (WWTP) that processes PFAS-laden water, 

used AFFF storage containers, or products associated with waterproofing uniforms or boots. 

Known release locations on Buckley SFB may have contributed to PFAS-containing waste being 

disposed of at the landfill; as such, Site 3 is considered an adjacent potential release area.

3.3.4 Waste Water Treatment Plants

There are no WWTPs located at the Buckley AASF. The Aurora WWTP is the nearest WWTP, 

and it is located approximately 6.3 miles northwest and downgradient of the facility, along Sand 

Creek. COARNG personnel stated during interviews that sanitary system sewers at the facility 

connect to the Denver Metro Wastewater Reclamation District. The Denver Metropolitan 

Wastewater Reclamation District includes the Robert W. Hite Treatment Facility, located 

approximately 12.5 miles northwest and downgradient of the facility, and serves an estimated 2 

million people via 60 local governments and special districts, including Aurora. Treated sludge 

from the Denver Metropolitan Wastewater Reclamation District facilities is used as fertilizer at 

the Metrogro Farm, located approximately 65 miles east of the City of Denver. Winter wheat, 

sorghum/sudan grass, and corn are grown at the Metrogro Farm, and pasture areas are often 

used for sheep and cattle grazing (Metro Wastewater Reclamation District, 2020).

WWTPs are not usually a primary potential release area of PFAS, but sludges and liquids from 

areas of potential release that are treated at WWTPs may create a secondary source of 

contamination. No known PFAS releases have occurred at the Buckley AASF, but adjacent 

AFFF releases could have resulted in the migration of PFAS in water to the Aurora WWTP, the 

Robert W. Hite Treatment Facility, and the Metrogro Farm. Agricultural products grown at the 

Metrogro Farm may create a potential pathway for human consumption of PFAS and expose 

grazing animals to PFAS. Due to the known adjacent AFFF releases surrounding the Buckley 

AASF, the Aurora WWTP, the Robert W. Hite Treatment Facility, and the Metrogro Farm are 

considered potential release areas. These locations are not shown on Figure 3-1 due to their 

distance from the Buckley AASF.
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­ Figure 3-1

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Germantown, MD 20876

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Site Inspection Report

Buckley AASF, Aurora, Colorado

AECOM 4-1

4. Project Data Quality Objectives

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

Assurance Project Plan (QAPP) Addendum (AECOM, 2022a), 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 may 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 Buckley AASF (AECOM, 2021);

• The Site Inspection Report of Aqueous Film Forming Foam Areas at Buckley Air Force

Base, Arapahoe County, Colorado (Aerostar SES LLC, 2019);

• 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, 2022a); 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). Temporal boundaries were limited to the summer season, which was the earliest available 

time field resources were available to complete the study. Vertical boundaries were established by 

the depth of the observed groundwater table. 

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, 2022a). 

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 
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AECOM 4-2

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

and qualitative methods, the assessment determines whether project execution and the 

resulting data have met installation-specific DQOs. Both sampling and analytical activities are 

considered to assess whether the collected data are of the right type, quality, and quantity to 

support the decision-making (DoD, 2019a; DoD, 2019b; USEPA, 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, 2022a). 
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Buckley AASF, Aurora, Colorado

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, Buckley Army Aviation Support Facility, Aurora,

Colorado dated February 2021 (AECOM, 2021);

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

Buckley Army Aviation Support Facility, Aurora, Colorado dated June 2022 (AECOM,

2022a); and

• Final Site Safety and Health Plan, Buckley Army Aviation Support Facility, Aurora,

Colorado dated July 2022 (AECOM, 2022b).

The SI field activities were conducted from 8 to 18 July 2022 and consisted of utility clearance,

sonic drilling, soil sample collection, permanent monitoring well installation, low-flow groundwater 

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

QAPP Addendum (AECOM, 2022a), except as noted in Section 5.8. 

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:

• Sixteen (16) soil samples from 10 boring locations;

• Three grab groundwater samples from three permanent wells;

• Seventeen (17) 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 Field Change 

Request Form is provided in Appendix B3, a Nonconformance and Corrective Action Report is 

provided in Appendix B4, and land survey data are provided in Appendix B5. Additionally, a 

photographic log of field activities is provided in Appendix C. 

5.1 Pre-Investigation Activities

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

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

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

5.1.1 Technical Project Planning

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

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

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

collection plan. The process encourages stakeholder involvement in the SI, beginning with 
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AECOM 5-2

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 16 March 2022, 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, COARNG, USACE, and the Colorado Department of 

Public Health and Environment (CDPHE). 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, 2022a). 

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

minutes for TPP 3 will be included in Appendix D of this report. Future TPP meetings will 

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

5.1.2 Utility Clearance 

AECOM placed a ticket with the Colorado 811 public utility clearance provider to notify them of 

intrusive work on 7 July 2022. Additionally, AECOM contracted Ground Penetrating Radar

Systems (GPRS), a private utility location service, to perform utility clearance. GPRS performed 

utility clearance of the proposed boring locations on 8 July 2022 with input from the AECOM 

field team and Buckley AASF facility staff. General locating services and ground-penetrating 

radar were used to complete the clearance. Additionally, the first 5 feet of each boring were precleared using a hand auger to verify utility clearance in shallow subsurface where utilities would 

typically be encountered. All subsurface activities were completed under a Base Civil 

Engineering Work Clearance Request (Air Force Form 103), or “dig permit”, issued by Buckley 

SFB. 

5.1.3 Source Water and Sampling Equipment Acceptability

Two potable water sources at Buckley AASF were sampled on 31 May 2022 to assess usability 

for decontamination of drilling equipment. Results of the sample collected at the spigot on the 

northeast exterior corner of Building 1510 (BKLY-DECON-01) confirmed this source to be 

acceptable for use in this investigation; therefore, it was used throughout the field activities.

Specifically, the samples were analyzed by LC/MS/MS compliant with QSM 5.3 Table B-15. The 

results of the decontamination water sample associated with the northeast exterior spigot 

source used during the SI are provided in Appendix F. A discussion of the results is presented 

in the DUA (Appendix A).

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

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

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

QAPP Addendum (AECOM, 2022a). Prior to the start of field work each day, a Sampling 

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

reminder to each field team member regarding the allowable materials within the sampling 

environment. 

5.2 Soil Borings and Soil Sampling

Borings were installed in unpaved areas where applicable, to avoid disturbing concrete or 

asphalt surfaces. Soil samples were collected via sonic drilling, in accordance with the SI QAPP 

Addendum (AECOM, 2022a). 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. 
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AECOM 5-3

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

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

sample approximately 2 feet above the groundwater table, and one subsurface soil sample at a 

mid-point between the surface and the groundwater table no deeper than 15 ft bgs. 

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

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

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

requirements. Observations and measurements were recorded on boring logs (Appendix E) 

and in a non-treated field logbook (i.e., composition notebook). Depth interval, recovery 

thickness, PID concentrations, moisture, relative density, color (using a Munsell soil color chart), 

and texture (using the USCS) were recorded. The boring logs are provided in Appendix E. 

Soil borings completed during the SI found sands and low to medium plasticity fines (silts with 

clay) as the dominant lithology of the unconsolidated sediments below the Buckley AASF. The 

borings were completed at depths between 45 and 57.5 feet bgs, with the bottom of the wells 

set between 40 and 51.5 feet bgs. These observations are consistent with the understood

alluvial deposits overlying weathered rock layers at the facility.

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, 2022a).

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.

The three borings were converted to permanent wells in accordance with the SI QAPP 

Addendum (AECOM, 2022a). Borings were installed in unpaved areas to avoid disturbing 

concrete or asphalt surfaces.

5.3 Permanent Well Installation and Groundwater Sampling

During the SI, three permanent monitoring wells were installed downgradient (BKLY-MW001 

and BKLY-MW002) or upgradient (BKLY-MW003) of potential source areas. The locations of the 

wells are shown on Figure 5-1. 

A sonic drill rig system was used to install three 2-inch diameter monitoring wells. The 

monitoring wells were constructed with Schedule 40 polyvinyl chloride (PVC), flush threaded 10-

foot sections of riser, 0.010-inch slotted well screen, and a threaded bottom cap. Water was not 

added during the drilling of the wells. A filter pack of 20/40 silica sand was installed in the 

annulus around the well screen to a minimum of 2-foot above the well screen. A 2-foot-thick 

bentonite seal was placed above the filter sand and hydrated with water. Bentonite grout was 

placed in the well annulus from the top of the bentonite seal to ground surface. The bentonite 

grout was allowed to set for 24 hours prior to well completion in accordance with the SI QAPP 

Addendum (AECOM, 2022a). All monitoring wells were completed with flush mount well vaults. 

The screen interval of each of the groundwater monitoring wells is provided in Table 5-2. 
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AECOM 5-4

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

(AECOM, 2022a). The newly installed monitoring wells were developed no sooner than 24 

hours 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 QED Sample Pro® bladder 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, dissolved oxygen, and

oxidation-reduction potential) 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 was any foaming. No foaming 

was noted in any of the groundwater samples.

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, 2022a).

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

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

same parameters as the accompanying samples. One field reagent blank was collected in 

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

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

5.4 Synoptic Water Level Measurements

A synoptic groundwater gauging event was performed on 18 July 2022. Groundwater elevation 

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

measurements were taken from the northern side of the well casing. A groundwater flow contour 

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

5.5 Surveying

The north side of each well casing was surveyed by Colorado-licensed land surveyors following 

guidelines provided in the SOPs provided in the SI QAPP Addendum (AECOM, 2022a). Survey 

data from the newly installed wells on the facility were collected on 15 July 2022 in the 

applicable Universal Transverse Mercator zone projection with Colorado State Plane Central 

Zone North American Datum 1983 (NAD83) (1992) datum (horizontal) and North American 

Vertical Datum 1988 (vertical). The surveyed well data are provided in Appendix B4. 

5.6 Investigation-Derived Waste

As of the date of this report, the disposal of 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, 2022a) and with the DA Guidance for 

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

Soil IDW (i.e., soil cuttings) generated during the SI activities were contained in labeled, 

55-gallon Department of Transportation (DOT)-approved steel drums filled 3/4 full to account for

freeze/thaw cycles and left onsite in a designated waste storage area. The soil IDW was not

sampled and assumes the characteristics of the associated soil samples collected from that

source location. Eight drums of soil remain on pallets at the site, staged on the pad immediately
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AECOM 5-5

southeast of Building 1025. ARNG will coordinate waste profiling, transportation, and disposal of 

the solid IDW under a separate contract. 

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

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

2/3 full to account for freeze/thaw cycles, and left onsite in a designated waste storage area. 

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

groundwater samples collected from that source location. Two drums of aqueous IDW remain

on pallets at the facility, staged on the pad immediately southeast of Building 1025.

Containerized liquid IDW will be managed and disposed of by ARNG (either by offsite disposal 

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

SOP No. 042A (EA, 2021). 

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

unused monitoring well construction materials, and other environmental media generated during 

the field activities were disposed of at a licensed solid waste landfill.

5.7 Laboratory Analytical Methods

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

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

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

9045D. 

5.8 Deviations from SI QAPP Addendum

Two deviations from the SI QAPP Addendum were identified during review of the field 

documentation. The deviations are noted below and documented in a Field Change Request 

Form (Appendix B3) and a Nonconformance and Corrective Action Report (Appendix B4): 

• During the site walk and utility clearance prior to subsurface investigations, it was deemed

appropriate to revise several boring and well locations as described below:

AOI 1

• Location AOI01-02 was moved approximately 180 feet southeast because a newly

constructed building blocked the original location. The new location is a low-lying

area outside new construction area, where flight ramp drainage most likely

encounters ground surface.

• Location AOI01-03 was moved approximately 50 feet northwest, from a hilltop to a

low-lying area immediately off the southeast flight ramp.

• Location AOI01-4 was moved approximately 170 feet southwest to be within the dry

retention basin at the southwest end of the flight ramp.

• Added location AOI01-5 at a low-lying area that receives drainage from the

southeast side of flight line.

• BKLY-MW001 was moved approximately 108 feet southeast of the original location

to be better situated downgradient from concentration of infiltration areas at AOI 1.

• BKLY-MW003 was moved approximately 420 feet southwest from the original

location, west of the short line to avoid conflicts with Zulu pad and Buckley SFB

Runway. The new location is positioned upslope from the flight ramp.
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AECOM 5-6

AOI 2

• The entire area where the Tri-MaxTM units were stored is paved and drains to

enclosed capture basin bordered by a concrete wall on three sides. AOI02-02 was

added where runoff from near AOI02-01 and the area east of Building 1510 drains.

• BKLY-MW002 was moved approximately 100 feet west of the original location to

get nearer to the downgradient low end of the retention basin.

The sample location changes and additions were made after the initial site visit to better 

meet data quality objectives relative to the original sample locations, which were placed 

only using aerial imagery. The new locations were approved in a discussion between 

AECOM and ARNG G-9 on June 3, 2022. The location changes are documented in a 

Field Change Request Form provided in Appendix B3.

• Upon review of field documentation, it was discovered that only one grain size analysis soil

sample was collected at the site, instead of one soil sample per AOI. This

omission was documented in a Nonconformance and Corrective Action Report provided in

Appendix B4.
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, Buckley AASF, Colorado

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-0-0.5 7/12/2022 12:35 0-0.5 x

AOI01-01-SB-0-0.5-D 7/12/2022 12:35 0-0.5 x Duplicate

AOI01-02-SB-0-2 7/13/2022 13:30 0-2 x x x

AOI01-02-SB-0-2-MS 7/13/2022 13:30 0-2 x x MS/MSD

AOI01-02-SB-0-2-MSD 7/13/2022 13:30 0-2 x x MS/MSD

AOI01-03-SB-0-2 7/13/2022 13:45 0-2 x

AOI01-03-SB-0-2-MS 7/13/2022 13:45 0-2 x MS/MSD

AOI01-03-SB-0-2-MSD 7/13/2022 13:45 0-2 x MS/MSD

AOI01-04-SB-0-2 7/13/2022 13:55 0-2 x

AOI01-05-SB-0-2 7/13/2022 13:50 0-2 x

AOI02-01-SB-0-2 7/12/2022 14:35 0-2 x x x

AOI02-01-SB-0-2-D 7/12/2022 14:35 0-2 x x Duplicate

AOI02-02-SB-0-2 7/12/2022 14:25 0-2 x

BKLY-MW001-SB-0-2 7/13/2022 13:00 0-2 x

BKLY-MW001-SB-13-15 7/13/2022 15:30 13-15 x

BKLY-MW001-SB-35-37 7/13/2022 16:05 35-37 x

BKLY-MW002-SB-0-2 7/12/2022 13:00 0-2 x

BKLY-MW002-SB-13-15 7/12/2022 16:15 13-15 x

BKLY-MW002-SB-13-15-D 7/12/2022 16:15 13-15 x Duplicate

BKLY-MW002-SB-35-37.5 7/12/2022 16:20 35-37.5 x

BKLY-MW002-SB-37.5 7/12/2022 16:25 37.5 x

BKLY-MW003-SB-0-2 7/14/2022 8:25 0-2 x

BKLY-MW003-SB-13-15 7/14/2022 10:40 13-15 x

BKLY-MW003-SB-43-45 7/14/2022 10:45 43-45 x

BKLY-MW001-071822 7/18/2022 14:50 NA x

BKLY-MW002-071822 7/18/2022 9:00 NA x

BKLY-MW002-071822-D 7/18/2022 9:00 NA x Duplicate

BKLY-MW002-071822-MS 7/18/2022 9:00 NA x MS/MSD

BKLY-MW002-071822-MSD 7/18/2022 9:00 NA x MS/MSD

BKLY-MW003-071822 7/18/2022 12:25 NA x

BKLY-ERB-01 7/13/2022 9:50 NA x

BKLY-ERB-02 7/13/2022 13:50 NA x

BKLY-ERB-03 7/18/2022 9:10 NA x

BKLY-FRB-01 7/13/2022 9:55 NA x

BKLY-DECON-01 5/31/2022 14:00 NA x

BKLY-DECON-02 5/31/2022 14:00 NA x

BKLY-DECON-03 7/13/2022 13:15 NA x

BKLY-ERB-01 = collected via decontaminated hand auger

BKLY-ERB-02 = collected via drilling shoe

BKLY-ERB-03 = collected via bladder pump

BKLY-FRB-01 = collected via running drill truck

BKLY-DECON-03 = collected via driller decontamination water

Soil Samples

Blank Samples

Groundwater Samples

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

AECOM 5-7
Table 5-2

Soil Boring Depths and Permanent Well Screen Intervals

Site Inspection Report, Buckley AASF, Colorado

Area of 

Interest

Boring 

Location

Monitoring 

Well ID

Soil Boring 

Depth 

(feet bgs)

Permanent Well 

Screen Interval 

(feet bgs)

1 BKLY-MW001 BKLY-MW001 47.5 31.5-41.5

1 BKLY-MW003 BKLY-MW003 57.5 41.5-51.5

2 BKLY-MW002 BKLY-MW002 45 30-40

Notes:

AASF = Army Aviation Support Facility

bgs = below ground surface

BKLY = Buckley

ID = identification

AECOM 5-8
Table 5-3

Depths to Water and Groundwater Elevations in Permanent Wells

Site Inspection Report, Buckley AASF, Colorado

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)

BKLY-MW001 31.5 - 41.5 5575.76 5575.85 38.28 38.37 5537.48

BKLY-MW002 30 - 40 5571.73 5571.64 33.89 33.80 5537.84

BKLY-MW003 41.5 - 51.5 5590.25 5590.50 44.76 45.01 5545.49

Notes:

bgs - below ground surface

btoc = below top of casing

ID = identification

NA = not available

NAVD88 = North American Vertical Datum 1988

AECOM 5-9
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AECOM 5-10

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"S

"S

"S

"S

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"S

Surface Impoundment

Stormwater Retention Pond

GSE Building Area

Building 1510

Former Tri-Max Storage Area

AOI 1

AOI 2

BKLY-MW001

BKLY-MW002

BKLY-MW003

AOI01-01

AOI01-02

AOI01-03

AOI01-04

AOI02-01

AOI02-02

AOI01-05

East Toll Gate Creek

­ Figure 5-1

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Buckley AASF, CO

1/23/2023

1/23/2023

1/23/2023

MS

AD

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GIS BY

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

1/23/2023

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Area of Interest

Potential Release Area

Facility Boundary

River/Stream

Surface Water Flow Direction

Groundwater Flow Direction

Site Inspection Sample Locations

12420 Milestone Center Drive 0 220 440 880 Germantown, MD 20876

Feet

AECOM 5-11
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5-12
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AECOM 6-1

6. Site Inspection Results

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

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

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

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

laboratory reports are provided in Appendix G. 

6.1 Screening Levels

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

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

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

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

SLs established in the 6 July 2022 OSD memorandum, the AOI will proceed to the next phase 

under CERCLA. The SLs established in the 6 July 2022 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 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. 

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

Buckley AASF, Aurora, Colorado

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: Building 1510. 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

Soil was sampled from surface soil (0 to 2 feet bgs) from boring locations AOI01-01 through 

AOI01-05, BKLY-MW001, and BKLY-MW003. Soil was also sampled from shallow subsurface 

soil (13 to 15 feet bgs) and deep subsurface soil intervals (35 to 45 feet bgs) from boring 

locations BKLY-MW001 and BKLY-MW003. Figure 6-1 through Figure 6-5 present the ranges 

of detections in soil. Table 6-2 through Table 6-4 summarize the soil results. 

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

respective SLs, with the highest found at AOI01-04 with a PFOS concentration of 1.94 μg/kg. 

PFBS was not detected in any AOI 1 surface soil samples. 

At BKLY-MW001 (downgradient of AOI 1), PFOA, PFOS, PFHxS, PFNA, and PFBS were not 

detected in subsurface soil.

At BKLY-MW003 (upgradient of AOI 1) PFOS, PFHxS, and PFBS were detected in shallow 

subsurface soil at concentrations less than their respective SLs, with the highest found at BKLYMW003 with a PFOS concentration of 0.398 J μg/kg. PFOA and PFNA were not detected in any 

shallow subsurface soil samples. PFHxS was detected in the deep subsurface soil at BKLYMW003, with a concentration of 0.045 J μg/kg. PFOA, PFOS, PFNA, and PFBS were not 

detected in deep subsurface soil at BKLY-MW003. 

6.3.2 AOI 1 Groundwater Analytical Results 

Groundwater was sampled from permanent monitoring wells BKLY-MW001 (downgradient well)

and BKLY-MW003 (upgradient well). Figure 6-6 and Figure 6-7 present the ranges of 

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

Buckley AASF, Aurora, Colorado

AECOM 6-3

The following exceedances of the SLs were measured in groundwater at AOI 1: 

BKLY-MW001 (downgradient well)

• PFOA was detected above the SL of 6 nanograms per liter (ng/L) in BKLY-MW001at a

concentration of 47.3 ng/L.

• PFOS was detected above the SL of 4 ng/L at BKLY-MW001, with a concentration of

7.31 J+ ng/L.

• PFHxS was detected above the SL of 39 ng/L at BKLY-MW001, with a concentrations

of 79.8 ng/L.

• PFBS was detected below its SL in BKLY-MW001, at a concentration of 20.7 ng/L.

PFNA was not detected at BKLY-MW001.

BKLY-MW003 (upgradient well)

• PFOA was detected above the SL of 6 nanograms per liter (ng/L) in BKLY-MW003 with

a concentration of 9.11 ng/L.

• PFOS was detected above the SL of 4 ng/L at BKLY-MW003 with a concentration of

20.4 J+ ng/L.

• PFHxS was detected above the SL of 39 ng/L at BKLY-MW003, with a concentration of

214 ng/L.

• PFBS was detected below its SL in BKLY-MW003, at a concentration of 50.7 ng/L.

PFNA was detected below its SL in BKLY-MW003, at a concentration of 1.12 J ng/L.

6.3.3 AOI 1 Conclusions

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

below their SLs. PFOA, PFOS, and PFHxS were detected in groundwater in both the upgradient 

and downgradient wells at concentrations above their SLs. The detections in upgradient well 

BKLY-MW003 suggests impacted groundwater is entering the facility at the upgradient facility 

boundary and is not attributable to ARNG activities. Based on the exceedances of the SLs 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: Former Tri-MaxTM Storage Area. The results in soil and groundwater are summarized on 

Table 6-2 through Table 6-5. Soil and groundwater results are presented on Figure 6-1 through 

Figure 6-7. 

6.4.1 AOI 2 Soil Analytical Results

Soil was sampled from surface soil (0 to 2 feet bgs) from boring locations AOI02-01, AOI02-02, 

and BKLY-MW002. Soil was also sampled from shallow subsurface soil (13 to 15 feet bgs) and 

deep subsurface soil intervals (35 to 37.5 feet bgs) from boring location BKLY-MW002. Figure 

6-1 through Figure 6-5 present the ranges of detections in soil. Table 6-2 through Table 6-4

summarize the soil results.

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

respective SLs, with the highest found at AOI02-02 with a PFOS concentration of 1.04 μg/kg. 
Site Inspection Report

Buckley AASF, Aurora, Colorado

AECOM 6-4

PFBS was not detected in any AOI 2 surface soil sample. PFOA, PFOS, PFHxS, PFNA, and 

PFBS were not detected in shallow subsurface soil.

PFOS, PFHxS, PFNA, and PFBS were detected in the deep subsurface soil at BKLY-MW002

with the highest being a PFOS concentration of 3.93 J μg/kg. PFOA was not detected in deep 

subsurface soil at AOI 2. 

6.4.2 AOI 2 Groundwater Analytical Results 

Groundwater was sampled from permanent monitoring well BKLY-MW002. Figure 6-6 and 

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

groundwater results. 

PFOA, PFOS, PFHxS, PFNA, and PFBS were all detected above their respective SLs. The 

following maximum detected exceedances of the SLs are measured in groundwater at AOI 2: 

• PFOA was detected above the SL of 6 ng/L, at a concentration of 1,530 ng/L.

• PFOS was detected above the SL of 4 ng/L, at a concentration of 19,900 J ng/L.

• PFHxS was detected above the SL of 39 ng/L, at a concentration of 8,170 ng/L.

• PFNA was detected above the SL of 6 ng/L, at a concentration of 847 ng/L.

• PFBS was detected above the SL of 601 ng/L at a concentration of 1,150 ng/L.

6.4.3 AOI 2 Conclusions

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

below their SLs. It should be noted that the highest concentrations of target analytes in soil were

from the deep soil/capillary fringe sample of BKLY-MW002 which, considering the non-detect 

results in surface soil at this location, suggests a groundwater source of contamination. PFOA, 

PFOS, PFHxS, PFNA, and PFBS were detected in groundwater at concentrations above their 

SLs. Based on the exceedances of the SLs in groundwater, further evaluation at AOI 2 is 

warranted. 
Table 6-2

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

Site Inspection Report, Buckley AASF

Analyte OSD Screening

Level a

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

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

PFHxS 130 ND U ND U ND U ND U 0.057 J ND U 0.041 J 0.058 J ND U 0.058 J 0.063 J

PFNA 19 ND U ND U ND U 0.038 J 0.055 J 0.069 J 0.054 J 0.059 J 0.276 J 0.382 J 0.022 J

PFOA 19 ND U ND U 0.138 J ND U ND U 0.139 J ND U 0.240 J 0.260 J 0.237 J ND U

PFOS 13 0.075 J ND UJ 0.073 J 0.249 J 1.94 1.08 0.690 J 0.576 J 0.183 J 1.04 0.282 J

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AASF Army Aviation Support Facility

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

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

DL detection limit

Notes ft feet

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

ID identification

JTN Johnstown

LCMSMS liquid chromatography with tandem mass spectrometry

LOD limit of detection

ND analyte not detected above the LOD

OSD Office of the Secretary of Defense

QSM Quality Systems Manual

Qual interpreted qualifier

SB soil boring

USEPA United States Environmental Protection Agency

μg/kg micrograms per kilogram

Area of Interest

Sample ID

Sample Date

Depth

AOI01-01-SB-(0.0-0.5)

07/12/2022

0-0.5 ft

BKLY-MW003-SB-(0-2)

07/14/2022

0-2 ft

AOI01-01-SB-(0.0-0.5)-D

07/12/2022

0-0.5 ft

AOI01-02-SB-(0-2)

07/13/2022

0-2 ft

BKLY-MW001-SB-(0-2)

07/13/2022

0-2 ft

AOI01-03-SB-(0-2)

07/13/2022

0-2 ft

AOI01-04-SB-(0-2)

07/13/2022

0-2 ft

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

Groundwater or Soil using USEPA’s Regional Screening Level Calculator. HQ=0.1, May 2022. Soil screening levels based on residential scenario

for incidental ingestion of contaminated soil.

AOI01 AOI02

BKLY-MW002-SB-(0-2)

07/12/2022

0-2 ft

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

AOI02-01-SB-(0-2)

07/12/2022

0-2 ft

AOI02-02-SB-(0-2)

07/12/2022

0-2 ft

AOI01-05-SB-(0-2)

07/13/2022

0-2 ft

AECOM 6-5
Table 6-3

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

Site Inspection Report, Buckley AASF

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual

PFBS 25000 ND U 0.150 J ND UPFHxS 1600 ND U 0.223 J ND UPFNA 250 ND U ND U ND UPFOA 250 ND U ND U ND U

PFOS 160 ND U 0.398 J 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 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 feet

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

ID identificationJTN JohnstownLCMSMS liquid chromatography with tandLOD limit of detectionND analyte not detected above the OSD Office of the Secretary of DefenQSM Quality Systems ManualQual interpreted qualifierSB soil boringUSEPA United States Environmental Prμg/kg micrograms per kilogram

07/13/2022

13-15 ft

AOI01

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

a. Assistant Secretary of Defense, July 2022. Risk Based Screening Levels Calculated for PFOA, PFOS, PFBS, PFHxS, and PFNA in Groundwater or Soil using USEPA’s Regional Screening Level Calculator. HQ=0.1, May 2022. Soil screening levels based on industrial/commercial composite worker scenario for incidental ingestion of contaminated soil.

AOI02

BKLY-MW002-SB-(13-15)

07/12/2022

13-15 ft

BKLY-MW003-SB-(13-15)

07/14/2022

13-15 ft

Area of Interest

Sample ID

Sample Date

Depth

BKLY-MW001-SB-(13-15)

AECOM 
Table 6-4

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

Site Inspection Report, Buckley AASF

Area of Interest

Sample ID

Sample Date

Depth

Analyte Result Qual Result Qual Result Qual Result Qual

PFBS ND U ND U 0.021 J 0.037 JPFHxS ND U 0.045 J 0.249 J 0.054 JPFNA ND U ND U 0.106 J ND UJ

PFOA ND U ND U ND U ND UPFOS ND U ND U 3.93 J 0.827 J

Interpreted Qualifiers Chemical AbbreviationsJ = Estimated concentration PFBS perfluorobutanesulfonJ+ = Estimated concentration, biased high PFHxS perfluorohexanesulfonU = The analyte was not detected at a level greater than or equal to the adjusted DL PFNA perfluorononanoic aciUJ = 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. PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfon

Notes

ND = Analyte not detected above the LOD. LOD values are presented in Appendix F. Acronyms and Abbreviations

AOI Area of InterestD duplicateDL detection limitft feetID identificationJTN JohnstownLCMSMS liquid chromatography LOD limit of detectionND analyte not detected aQSM Quality Systems ManuQual interpreted qualifierSB soil boringμg/kg micrograms per kilogr

AOI01

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

AOI02

BKLY-MW002-SB-(35-37.5)-D

07/12/2022

35-37.5 ft

BKLY-MW003-SB-(43-45)

07/14/2022

43-45 ft

BKLY-MW001-SB-(35-37)

07/13/2022

35-37 ft

BKLY-MW002-SB-(35-37.5)

07/12/2022

35-37.5 ft

AECOM 
Table 6-5

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

Site Inspection Report, Buckley AASF

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual

PFBS 601 20.7 50.7 1150 1040PFHxS 39 79.8 214 7660 J 8170PFNA 6 ND U 1.12 J 847 777PFOA 6 47.3 9.11 1530 1410

PFOS 4 7.31 J+ 20.4 J+ 19900 J 16400

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

BKLY Buckley

Notes D duplicate

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

GW groundwaterHQ hazard quotientID identificationLCMSMS liquid chromatography with tandem LOD limit of detectionND analyte not detected above the LOOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierUSEPA United States Environmental Proteng/l nanogram per liter

AOI01

BKLY-MW003-071822

07/18/2022

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

a. Assistant Secretary of Defense, July 2022. Risk Based Screening Levels Calculated for PFOA, PFOS, PFBS, PFHxS, and PFNA in Groundwater or Soil using USEPA’s Regional Screening Level Calculator. HQ=0.1, May 2022 Groundwater screening levels based on residential scenario for direct ingestion of groundwater.

AOI02

BKLY-MW002-071822

07/18/2022

BKLY-MW002-071822-D

07/18/2022

Area of Interest

Sample ID

Sample Date

BKLY-MW001-071822

07/18/2022

AECOM 
BKLY-MW001

ND

BKLY-MW002

ND

BKLY-MW003

0.24 μg/Kg

AOI01-01

ND

AOI01-02

0.138 μg/Kg

AOI01-03

ND

AOI01-04

ND

AOI02-01

AOI02-02 0.26 μg/Kg

0.237 μg/Kg

AOI01-05

0.139 μg/Kg

­ Figure 6-1

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Ins pe c tion at Buc kle y AASF, CO

8/31/2023

8/31/2023

8/31/2023

M S

AD

CM

GIS BY

CHK BY

PM

Bas e M ap: Sourc e : Es ri, M axar, Earths tar Ge ographic s , and the GIS Us e r Com m unity

8/31/2023

1:3,600

Fac ility Bound ary

PFOA Detections in Soil

12420 M ile s tone Ce nte r Drive

Ge rm antow n, M D 20876

0 150 300 600

Fe e t

BKLY-MW001

ND

BKLY-MW002

ND

BKLY-MW003

ND

BKLY-MW001

ND

BKLY-MW002

ND

BKLY-MW003

ND

Shallow Inte rm e d iate De e p

ND = Not De te c te d

Exc e e d anc e s of the OSD SL are d e pic te d w ith a ye llow halo.

De pth inte rvals s how n re pre s e nt re s pe c tive s am pling pos ition w ithin a give n s oil boring loc ation.

PFOA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

AECOM 6-9
BKLY-MW001

0.69 μg/Kg

BKLY-MW002

0.282 μg/Kg

BKLY-MW003

0.576 μg/Kg

AOI01-01

0.075 μg/Kg

AOI01-02

0.073 μg/Kg

AOI01-03

0.249 μg/Kg

AOI01-04

1.94 μg/Kg

AOI02-01

AOI02-02 0.183 μg/Kg

1.04 μg/Kg

AOI01-05

1.08 μg/Kg

­ Figure 6-2

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Ins pe c tion at Buc kle y AASF, CO

8/31/2023

8/31/2023

8/31/2023

M S

AD

CM

GIS BY

CHK BY

PM

Bas e M ap: Sourc e : Es ri, M axar, Earths tar Ge ographic s , and the GIS Us e r Com m unity

8/31/2023

1:3,600

Fac ility Bound ary

PFOS Detections in Soil

12420 M ile s tone Ce nte r Drive

Ge rm antow n, M D 20876

0 150 300 600

Fe e t

BKLY-MW001

ND

BKLY-MW002

ND

BKLY-MW003

0.398 μg/Kg

BKLY-MW001

ND

BKLY-MW002

3.93 μg/Kg

BKLY-MW003

ND

Shallow Inte rm e d iate De e p

ND = Not De te c te d

Exc e e d anc e s of the OSD SL are d e pic te d w ith a ye llow halo.

De pth inte rvals s how n re pre s e nt re s pe c tive s am pling pos ition w ithin a give n s oil boring loc ation.

PFOS Results (μg/Kg)

ND

>ND - 13

>13 - 160

>160 - 1,600

>1,600

AECOM 6-10
BKLY-MW001

ND

BKLY-MW002

ND

BKLY-MW003

ND

AOI01-01

ND

AOI01-02

ND

AOI01-03

ND

AOI01-04

ND

AOI02-01

ND

AOI02-02

ND

AOI01-05

ND

­ Figure 6-3

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Ins pe c tion at Buc kle y AASF, CO

8/31/2023

8/31/2023

8/31/2023

M S

AD

CM

GIS BY

CHK BY

PM

Bas e M ap: Sourc e : Es ri, M axar, Earths tar Ge ographic s , and the GIS Us e r Com m unity

8/31/2023

1:3,600

Fac ility Bound ary

PFBS Detections in Soil

12420 M ile s tone Ce nte r Drive

Ge rm antow n, M D 20876

0 150 300 600

Fe e t

BKLY-MW001

ND

BKLY-MW002

ND

BKLY-MW003

0.15 μg/Kg

BKLY-MW001

ND

BKLY-MW002

0.037 μg/Kg

BKLY-MW003

ND

Shallow Inte rm e d iate De e p

ND = Not De te c te d

Exc e e d anc e s of the OSD SL are d e pic te d w ith a ye llow halo.

De pth inte rvals s how n re pre s e nt re s pe c tive s am pling pos ition w ithin a give n s oil boring loc ation.

PFBS Results (μg/Kg)

ND

>ND - 10

>10 - 1,900

>1,900 - 25,000

>25,000

AECOM 6-11
BKLY-MW001

0.041 μg/Kg

BKLY-MW002

0.063 μg/Kg

BKLY-MW003

0.058 μg/Kg

AOI01-01

ND

AOI01-02

ND

AOI01-03

ND

AOI01-04

0.057 μg/Kg

AOI02-01

ND

AOI02-02

0.058 μg/Kg

AOI01-05

ND

­ Figure 6-4

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Ins pe c tion at Buc kle y AASF, CO

8/31/2023

8/31/2023

8/31/2023

M S

AD

CM

GIS BY

CHK BY

PM

Bas e M ap: Sourc e : Es ri, M axar, Earths tar Ge ographic s , and the GIS Us e r Com m unity

8/31/2023

1:3,600

Fac ility Bound ary

PFHxS Detections in Soil

12420 M ile s tone Ce nte r Drive

Ge rm antow n, M D 20876

0 150 300 600

Fe e t

BKLY-MW001

ND

BKLY-MW002

ND

BKLY-MW003

0.223 μg/Kg

BKLY-MW001

ND

BKLY-MW002

0.249 μg/Kg

BKLY-MW003

0.045 μg/Kg

Shallow Inte rm e d iate De e p

ND = Not De te c te d

Exc e e d anc e s of the OSD SL are d e pic te d w ith a ye llow halo.

De pth inte rvals s how n re pre s e nt re s pe c tive s am pling pos ition w ithin a give n s oil boring loc ation.

PFHxS Results (μg/Kg)

ND

>ND - 10

>10 - 130

>130 - 1,600

>1,600

AECOM 6-12
BKLY-MW001

0.054 μg/Kg

BKLY-MW002

0.022 μg/Kg

BKLY-MW003

0.059 μg/Kg

AOI01-01

ND

AOI01-02

ND

AOI01-03

0.038 μg/Kg

AOI01-04

0.055 μg/Kg

AOI02-01

AOI02-02 0.276 μg/Kg

0.382 μg/Kg

AOI01-05

0.069 μg/Kg

­ Figure 6-5

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Ins pe c tion at Buc kle y AASF, CO

8/31/2023

8/31/2023

8/31/2023

M S

AD

CM

GIS BY

CHK BY

PM

Bas e M ap: Sourc e : Es ri, M axar, Earths tar Ge ographic s , and the GIS Us e r Com m unity

8/31/2023

1:3,600

Fac ility Bound ary

PFNA Detections in Soil

12420 M ile s tone Ce nte r Drive

Ge rm antow n, M D 20876

0 150 300 600

Fe e t

BKLY-MW001

ND

BKLY-MW002

ND

BKLY-MW003

ND

BKLY-MW001

ND

BKLY-MW002

0.106 μg/Kg

BKLY-MW003

ND

Shallow Inte rm e d iate De e p

ND = Not De te c te d

Exc e e d anc e s of the OSD SL are d e pic te d w ith a ye llow halo.

De pth inte rvals s how n re pre s e nt re s pe c tive s am pling pos ition w ithin a give n s oil boring loc ation.

PFNA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

AECOM 6-13
BKLY-MW001

47.3 ng/L

BKLY-MW002

1530 ng/L

BKLY-MW003

9.11 ng/L

­ Figure 6-6

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Buckley AASF, CO

8/31/2023

8/31/2023

8/31/2023

MS

AD

CM

GIS BY

CHK BY

PM

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

8/31/2023

1:3,600

Facility Boundary

Groundwater Flow Direction

PFOA, PFOS, and PFBS Detections in Groundwater

12420 Milestone Center Drive

Germantown, MD 20876

0 150 300 600

Feet

BKLY-MW001

7.31 ng/L

BKLY-MW002

19900 ng/L

BKLY-MW003

20.4 ng/L

BKLY-MW001

20.7 ng/L

BKLY-MW002

1150 ng/L

BKLY-MW003

50.7 ng/L

PFOA PFOS PFBS

ND = Not Detected

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

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 6-14
BKLY-MW001

79.8 ng/L

BKLY-MW002

8170 ng/L

BKLY-MW003

214 ng/L

­ Figure 6-7

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Buckley AASF, CO

8/31/2023

8/31/2023

8/31/2023

MS

AD

CM

GIS BY

CHK BY

PM

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

8/31/2023

1:3,600

Facility Boundary

Groundwater Flow Direction

PFHxS and PFNA Detections in Groundwater

12420 Milestone Center Drive

Germantown, MD 20876

0 150 300 600

Feet

BKLY-MW001

ND

BKLY-MW002

847 ng/L

BKLY-MW003

1.12 ng/L

PFHxS PFNA

ND = Not Detected

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

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 6-15
THIS PAGE INTENTIONALLY BLANK

6-16
Site Inspection Report

Buckley AASF, Aurora, Colorado

AECOM 7-1

7. Exposure Pathways

The CSMs for each AOI, revised based on the SI findings, are presented on Figure 7-1 through 

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

be impacted, the decision to move from SI to 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 a RI or no action at this time is based on the comparison of 

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

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

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

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

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

receptors evaluated are consistent with those listed in USEPA guidance for risk screening 

(USEPA, 2001). Receptors at the facility include site workers (e.g., facility staff and visiting 

soldiers), construction workers, trespassers (though unlikely due to restricted access), residents 

outside the facility boundary, and recreational users outside of the facility boundary. 

7.1 Soil Exposure Pathway

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

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

criteria. 

7.1.1 AOI 1 

AOI 1 is Building 1510, which is constructed with a HEF deluge fire suppression system that 

contains 900 gallons of Ansul Jet-X 2.75% HEF concentrate. A 55-gallon drum containing the 

same HEF concentrate product is also stored within Building 1510. The HEF deluge fire 

suppression system was tested in 2006 with a 3-minute discharge of an unknown volume of 

Ansul Jet-X 2.75% HEF to the hangar area. It is unclear whether the HEF product released at 
Site Inspection Report

Buckley AASF, Aurora, Colorado

AECOM 7-2

Buckley AASF contained PFAS; however, it is conservatively assumed to have for the purpose 

of the investigation. 

PFOA, PFOS, PFHxS, and PFNA were detected in surface soil at AOI 1. Site workers and 

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

inhalation of dust. Therefore, the airborne soil particulate and surface soil exposure pathways 

for site workers and construction workers are potentially complete. Buckley SFB is a secure 

facility and there are no immediate nearby residential structures. Therefore, the incidental 

ingestion and inhalation of dust exposure pathways for the trespassers, recreational users, and 

residential receptors incomplete. 

PFOS, PFHxS, and PFBS were detected in subsurface soil at AOI 1. Construction workers 

could contact constituents in subsurface soil via incidental ingestion, and therefore, the 

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

AOI 1 is presented on Figure 7-1. 

7.1.2 AOI 2 

AOI 2 encompasses the area in the northeastern portion of the facility formerly used to store six 

Tri-MaxTM wheeled fire extinguishers containing Chemguard 3% C-303 AFFF concentrate. The 

Tri-MaxTM units were removed and disposed of in a controlled manner in September 2019. 

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

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

inhalation of dust. Therefore, the airborne soil particulate and surface soil exposure pathways 

for site workers and construction workers are potentially complete. Buckley SFB is a secure 

facility and there are no immediate nearby residential structures. Therefore, the incidental 

ingestion and inhalation of dust exposure pathways for the trespassers, recreational users, and 

residential receptors incomplete. PFOA, PFOS, PFHxS, and PFNA in subsurface soil at AOI 2 

were only detected at depths greater than 15 feet bgs.; therefore, all exposure pathways are 

considered incomplete because 15 feet bgs is considered the extent of excavation for the 

construction worker scenario. The CSM for AOI 2 is presented on Figure 7-2. 

7.2 Groundwater Exposure Pathway

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

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

7.2.1 AOI 1 

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

samples collected at AOI 1. Buckley AASF is a secure facility with restricted access; therefore, 

the ingestion exposure pathway for trespassers is considered incomplete. Due to the presence 

of public water system wells and domestic wells within a 4-mile radius of the facility in the 

downgradient direction, the pathway for exposure to off-facility residents via ingestion of 

groundwater is considered potentially complete. Because the location of City of Aurora drinking 

water groundwater wells that may serve the AASF are unknown, the pathway for exposure to 

site workers via ingestion of groundwater is also considered potentially complete. Depth to 

water at AOI 1 in July 2022 during the SI was measured at 38.57 feet bgs. Therefore, the 

ingestion exposure pathway for construction workers is considered incomplete. The CSM for 

AOI 1 is presented on Figure 7-1. 
Site Inspection Report

Buckley AASF, Aurora, Colorado

AECOM 7-3

7.2.2 AOI 2 

PFOA, PFOS, PFHxS, PFNA, and PFBS were detected at concentrations above their SLs in 

groundwater samples collected at AOI 2. Buckley AASF is a secure facility with restricted 

access; therefore, the ingestion exposure pathway for trespassers is considered incomplete. 

Due to the presence of public water system wells and domestic wells within a 4-mile radius of 

the facility in the downgradient direction, the pathway for exposure to off-facility residents via 

ingestion of groundwater is considered potentially complete. For the same reasons described 

above, the pathway for exposure to site workers via ingestion of groundwater is also considered 

potentially complete. Depth to water at AOI 2 in July 2022 during the SI was measured at 34.13 

feet bgs. Therefore, the ingestion exposure pathway for construction workers is considered 

incomplete. The CSM for AOI 2 is presented on Figure 7-2. 

7.3 Surface Water and Sediment Exposure Pathway

The SI results in in soil and groundwater, in combination with knowledge of the fate and 

transport properties of PFAS, were used to determine whether a potentially complete pathway 

exists between the source and potential receptors.

PFAS are water soluble and can migrate readily from soil to surface water via leaching and 

runoff. Because PFOA, PFOS, PFHxS, PFNA, and PFBS were detected in soil and/or 

groundwater at AOI 1 and AOI 2, it is possible that those compounds may have migrated from 

soil and groundwater to the small emergent stream to the northeast of the facility, ultimately 

discharging to the East Toll Gate Creek and the South Platte River (USFWS, 2020). In addition, 

the City of Aurora, which supplies drinking water for Buckley AASF and surrounding residents, 

draws most of its water from surface sources. Therefore, the surface water and sediment 

ingestion exposure pathway for site workers, construction workers, residents, and recreational 

users is considered potentially complete. The CSM for AOI 1 is presented on Figure 7-1, and 

the CSM for AOI 2 is presented on 7-2. 
Site Inspection Report

Buckley AASF, Aurora, Colorado

AECOM 7-4

THIS PAGE INTENTIONALLY BLANK
Media

SOURCE PATHWAY RE

AOI 1 Surface soil

Human 

activities

Precipitation/ 

run-off

Leaching/ 

infiltration

Airborne soil 

particulate

Surface soil 

at AOI

Surface 

water/ 

sediment

Subsurface 

soil

Shallow 

groundwater

Source Release Mechanism Media Transport and Migration Media Exposure Routes

Inhalation of 

dust

Ingestion

Ingestion

Ingestion

Ingestion

Hum

C

Flow-Chart ContinuesPartial/ Possible FlowFlow-Chart StopsIncomplete PathwayPotentially Complete PathwayPotentially Complete Pathway with Exceedance of SL

Site 

Worker

Cons

Wo

Site 

Worker

Cons

Wo

/ / 

LEGEND

Figure 

Conceptual Site M

Buckley A

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

1. The resident and recreational users refer to offsite receptors.2. Inhalation of dust for off-site receptors is likelyinsignificant.3. No current active construction at the facility.Notes:

Building 1510 HEF 

System Test

/ / / 

AECOM 
Media

SOURCE PATHWAY RE

AOI 2 Surface soil

Human 

activities

Precipitation/ 

run-off

Leaching/ 

infiltration

Airborne soil 

particulate

Surface soil 

at AOI

Surface 

water/ 

sediment

Subsurface 

soil

Shallow 

groundwater

Source Release Mechanism Media Transport and Migration Media Exposure Routes

Inhalation of 

dust

Ingestion

Ingestion

Ingestion

Ingestion

Hum

C

Flow-Chart ContinuesPartial/ Possible FlowFlow-Chart StopsIncomplete PathwayPotentially Complete PathwayPotentially Complete Pathway with Exceedance of SL

Site 

Worker

Cons

Wo

Site 

Worker

Cons

Wo

/ / 

LEGEND

Figure 

Conceptual Site M

Buckley A

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

1. The resident and recreational users refer to offsite receptors.2. Inhalation of dust for off-site receptors is likelyinsignificant.3. No current active construction at the facility.Notes:

Former Tri-MaxTM

Storage Area

/ / / 

AECOM 
Site Inspection Report

Buckley AASF, Aurora, Colorado

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 8 to 18 July 2022 and consisted of utility clearance, 

sonic drilling, soil sample collection, permanent monitoring well installation, low-flow groundwater 

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

QAPP Addendum (AECOM, 2022a), except as previously noted in Section 5.8. 

To fulfill the project DQOs set forth in the approved SI QAPP Addendum (AECOM, 2022a), 

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. 

• Sixteen (16) soil samples from 10 boring locations;

• Three grab groundwater samples from three permanent wells;

• Seventeen (17) quality assurance QA/QC.

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 under CERCLA is warranted in an RI for AOI 1

and AOI 2 (see Table 8-1). Based on the CSMs developed and revised in light of the SI findings, 

there is potential for exposure to drinking water receptors from AOI 1 and AOI 2. Sample 

analytical concentrations collected during the SI were compared to the project SLs in soil and

groundwater, as described in Table 6-1. A summary of the results of the SI data relative to the 

SLs is as follows: 

• At AOI 1:

• The detected concentrations of PFOA, PFOS, PFHxS, PFNA, and PFBS in soil at

AOI 1 were below their SLs.

• At downgradient location BKLY-MW001, PFOA, PFOS, and PFHxS in groundwater

exceeded their SLs. PFOA exceeded the SL of 6 ng/L with a concentration of 47.3

ng/L; PFOS exceeded the SL of 4 ng/L, with a concentration of 7.31 ng/L; and

PFHxS exceeded the SL of 39 ng/L, with a concentration of 79.8 ng/L

• At upgradient location BKLY-MW003, PFOA, PFOS, and PFHxS in groundwater

exceeded their SLs. PFOA exceeded the SL of 6 ng/L, with a concentration of 9.11
Site Inspection Report

Buckley AASF, Aurora, Colorado

AECOM 8-2

ng/L; PFOS exceeded the SL of 4 ng/L, with a concentration of 20.4 ng/L; and 

PFHxS exceeded the SL of 39 ng/L, with a concentration of 214 ng/L. 

• Based on the results of the SI, particularly the detections in groundwater at BKLYMW003, there is evidence of contaminated groundwater entering the facility at the

upgradient boundary that is not attributable to ARNG activities. Further evaluation

of AOI 1 is warranted in the RI.

• At AOI 2:

• The detected concentrations of PFOA, PFOS, PFHxS, PFNA, and PFBS in soil at

AOI 2 were below their SLs.

• PFOA, PFOS, PFHxS, PFNA, and PFBS were detected in regular and duplicate

groundwater samples, at concentrations above respective SLs. PFOA exceeded

the SL of 6 ng/L, with a maximum concentration of 1,530 ng/L. PFOS exceeded

the SL of 4 ng/L, with a maximum concentration of 19,900 J ng/L. PFHxS

exceeded the SL of 39 ng/L, with a maximum concentration of 8,170 ng/L in the

duplicate sample. PFNA exceeded the SL of 6 ng/L, with a maximum

concentration of 847 ng/L. PFBS exceeded the SL of 601 ng/L, with a

concentration of 1,150 ng/L. Based on the results of the SI, further evaluation of

AOI 2 is warranted in the RI.

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. The 

detections in upgradient well BKLY-MW003 suggests impacted groundwater is entering the 

facility at the upgradient facility boundary and is not attributable to ARNG activities.

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 Building 1510 NS Proceed to RI 

2

Former TriMaxTM 

Storage Area

NS Proceed to RI

Legend:

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected

NS = not sampled
Site Inspection Report

Buckley AASF, Aurora, Colorado

AECOM 9-1

9. References

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Project Plan, Perfluorooctane Sulfonic Acid (PFOS) and Perfluorooctanoic Acid (PFOA) 

Impacted Sites ARNG Installations, Nationwide Contract No. W912DR-12-D-0014/

W912DR17F0192. 9 March.

AECOM. 2018b. Final Programmatic Accident Prevention Plan, Perfluorooctane Sulfonic Acid 

(PFOS) and Perfluorooctanoic Acid (PFOA) Impacted Sites ARNG Installations, Nationwide 

Contract No. W912DR-12-D-0014/W912DR17F0192. July.

AECOM. 2021. Final Preliminary Assessment Report, Buckley Army Aviation Support Facility, 

Colorado. February. 

AECOM. 2022a. Final Site Inspection Uniform Federal Policy-Quality Assurance Project Plan 

Addendum, Buckley Army Aviation Support Facility, Aurora, Colorado, Perfluorooctane 

Sulfonic Acid (PFOS) and Perfluorooctanoic Acid (PFOA) Impacted Sites ARNG 

Installations, Nationwide. June. 

AECOM. 2022b. Final Site Safety and Health Plan, Buckley Army Aviation Support Facility, 

Aurora, Colorado, Perfluorooctane Sulfonic Acid (PFOS) and Perfluorooctanoic Acid (PFOA) 

Impacted Sites ARNG Installations, Nationwide. July. 

Aerostar SES LLC. 2019. Final Site Inspection Report of Aqueous Film Forming Foam Areas at 

Buckley Air Force Base, Arapahoe County, Colorado. April 2019.

Assistant Secretary of Defense. 2022. Investigation Per- and Polyfluoroalkyl Substances within 

the Department of Defense Cleanup Program. United States Department of Defense. 

6 July. 

COARNG, 2017. Spill Prevention, Control and Countermeasure Plan; Army Aviation Support 

Facilities: Buildings 1500, 1510, and 1515. Buckley AFB, Colorado.

DA. 2018. Army Guidance for Addressing Releases of Per- and Polyfluoroalkyl Substances.

4 September.

DoD. 2019a. Department of Defense (DoD), Department of Energy (DOE) Consolidated Quality 

Systems Manual (QSM) for Environmental Laboratories, Version 5.3. 

DoD. 2019b. General Data Validation Guidelines. Environmental Data Quality Workgroup. 

4 November.

EA Engineering Science and Technology, 2021. SOP No. 042A for Treating Liquid InvestigationDerived Material (Purge water, drilling water, and decontamination fluids).

Guelfo, J.L. and Higgins, C.P. 2013. Subsurface Transport Potential of Perfluoroalkyl Acids at 

Aqueous Film-Forming Foam (AFFF)-Impacted Sites. Environmental Science and 

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Higgins, C.P., and Luthy, R.G. 2006. Sorption of perfluorinated surfactants on 

sediments. Environmental Science and Technology 40 (23): 7251-7256.

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Buckley AASF, Aurora, Colorado

AECOM 9-2

National Oceanic and Atmospheric Administration, 2022. NOWData – NOAA Online Weather 

Data. Monthly Mean Avg Temperature for Denver Area, CO (ThreadEx).

https://www.weather.gov/wrh/Climate?wfo=bou. Accessed April 2022.

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https://www.sacwsd.org/DocumentCenter/View/1648/SACWSD-Water-Quality-Report-2021

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USEPA. 1980. Comprehensive Environmental Response, Compensation, and Liability Act 

(CERCLA). 

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40 CFR Part 300; 59 Federal Register 47384. September.

USEPA. 2001. Risk Assessment Guidance for Superfund, Volume I: Human Health Evaluation 

Manual (Part D, Standardized Planning, Reporting, and Review of Superfund Risk 

Assessments). December.

USEPA. 2014. Record of Decision: Site 3 (Former Base Landfill). Buckley Air Force Base.

Prepared By United States Air Force, 460th Space Wing, Buckley AFB, Colorado. March 

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Air Force Base. Prepared for United States Air Force, Aurora, Colorado. December 2019.

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https://www.fws.gov/wetlands/data/mapper.html. (Accessed December 2019).

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Conservation. Accessed 11 October 2022 at

https://ipac.ecosphere.fws.gov/location/JDWDR353AZBYXJOP3SG6GD22XU/resources

Xiao, F., Simcik, M. F., Halbach, T. R., and Gulliver, J. S. 2015, Perfluorooctane sulfonate 

(PFOS) and perfluorooctanoate (PFOA) in soils and groundwater of a U.S. metropolitan 

area: Migration and implications for human exposure. Water Research 72: 64-74.