Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

backfilling the hole with Portland cement. Borings were installed in asphalt and asphalt chipped
areas and were patched at the surface with similar material.

5.4 SYNOPTIC WATER LEVEL MEASUREMENTS

A synoptic groundwater gauging event was performed on 13 February 2023. Groundwater
elevation measurements were collected from the six new temporary monitoring wells. Water
level measurements were taken from the survey mark on the northern side of the well casing.
Groundwater elevation data is provided in Table 5-3. A groundwater flow contour map is
provided as Figure 2-4.

5.5 SURVEYING

The northern side of each new temporary well casing was surveyed using a Trimble R10 real-
time kinematic differential global positioning system. Positions were collected in the applicable
Universal Transverse Mercator zone projection with World Geodetic System 1984 datum
(horizontal) and North American Vertical Datum 1988 (vertical). Surveying data were collected
on 13 February 2022 and are provided in Appendix B3.

5.6 INVESTIGATION-DERIVED WASTE

As of the date of this report, the disposal of PFAS IDW is not regulated federally. IDW
generated during the SI is considered non-hazardous waste and was managed in accordance with
the UFP-QAPP Addendum (EA/Wood, 2022a).

Soil IDW (i.e., soil cuttings) and liquid IDW (i.e., purge water, development water, and
decontamination fluids) generated during the SI activities were drummed and stored within the
Facility. The soil IDW was not sampled and assumes the characteristics of the associated soil
samples collected from that source location.

Liquid IDW generated during SI activities (i.e., purge water, development water, and
decontamination fluids) were contained in labeled, 55-gallon Department of Transportation
approved steel drums, 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.

Geographic coordinates were collected using a Global positioning system (GPS) around each
location where IDW was placed (i.e., an IDW polygon). The IDW polygons are displayed on the
figure in Appendix B5,

The IDW disposal is being managed separately under a contract with EA Engineering, Science,
and Technology, Inc. Specifics on the disposal of solid and liquid IDW will be addressed in an
IDW Technical Memorandum.

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.

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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

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 was
implemented in accordance with the following approved documents.

e Final Preliminary Assessment Report, Cheyenne Army Aviation Support Facility,
Las Vegas, Nevada, dated July 2020 (AECOM, 2020)

¢ Final Programmatic Uniform Federal Policy-Quality Assurance Project Plan,
Site Inspections for Per- and Polyfluoroalkyl Substances Impacted Sites, ARNG
Installations, Nationwide, dated December 2020 (EA, 2020a)

e Final Site Inspection Uniform Federal Policy-Quality Assurance Project Plan
Addendum, Cheyenne Army Aviation Support Facility, Las Vegas, Nevada, dated
March 2022 (Wood 2022a)

e Final Programmatic Accident Prevention Plan, Revision 1, dated November 2020
(EA, 2020b)

e Final Accident Prevention Plan/Site Safety and Health Plan, Cheyenne Army
Aviation Support Facility, Las Vegas, Nevada, dated February 2022 (EA/Wood,
2022b).

The SI field activities were conducted from 30 January to 13 February 2023 and
consisted of utility clearance, boring advancement and soil sample collection, temporary
monitoring well installation, grab groundwater sample collection, and land surveying.
Following three failed attempts by hollow-stem auger to reach target boring depths
between 30 January and 1 February 2023, a rotosonic drill rig was mobilized to the
Facility on 9 February 2023 and used to complete the soil borings. Field activities were
conducted in accordance with the UFP-QAPP Addendum (EA/Wood 2022a), except as
noted in Section 5.8.

The following samples were collected during the SI and analyzed for 24 compounds via
liquid chromatography/tandem mass spectrometry (LC/MS/MS) compliant with QSM
Version 5.3 Table B-15 to fulfill the project DQOs:

e 15 soil samples from five boring locations;
¢ Six grab groundwater samples from six temporary well locations;
e Nine quality assurance (QA)/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 medium. Field documentation is provided
in Appendix B. A log of Daily Notice of Field Activity was completed throughout the SI
field activities, which is provided in Appendix B1. Sampling forms are provided in
Appendix B2, land survey data are provided in Appendix B3, a Field Change Request
form provided in Appendix B4, and investigation-derived waste (IDW) polygons are
provided in Appendix B5. Additionally, a photographic log of field activities is provided
in Appendix C.

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Site Inspection Report
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Version: FINAL

Table 5-3

Site Inspection Report

Groundwater Elevation
Cheyenne Army Aviation Support Facility, Las Vegas, Nevada

Top of Casing | Ground Surface Groundwater
Elevation Eleyation Depth to Water| Depth to Water Elevation

Monitoring Well ID|__(ft NAVD88) (ft NAVD88) (ft btoc) (ft bgs) (ft NAVD 88)
AOI01-01 2206.78 2204.52 33.91 31.65 2172.87
AOI01-02 2205.80 2205.82 33.77 33.79 2172.03
AOI02-01 2204.30 2202.65 30.61 28.96 2173.69
AOI02-02 2203.38 2201.28 29.90 27.80 2173.48
AASF-01 2208.46 2204.18 34.45 30.17 2174.01
AASF-02 2206.82 2204.78 32.86 30.82 2173.96

Notes:

' Temporary well screen set above total depth to capture groundwater interface

AASF = Army Aviation Support Facility

amsl = Above mean sea level

bgs = below ground surface

btoc = below top of casing

NA = not applicable

NAVD88 = North American Vertical Datum 1988

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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

No relevant compounds (PFBS, PFHxS, PFNA, PFOS, and PFOA) were detected in shallow and
deep subsurface soils.

6.4.2 AOI 2 Groundwater Analytical Results

Groundwater samples were collected from three temporary wells associated with AOI 2 during
the SI. Figure 6-6 and Figure 6-7 presents the ranges of detections in groundwater. Table 6-5
summarizes the groundwater results.

Groundwater was sampled from temporary monitoring well locations AOI02-01, AOI02-02, and
AASF-01, located upgradient of AOI 2. PFOS was detected in groundwater at a concentration
above the SL. PFBS, PFHxS, and PFOA were detected in groundwater at concentrations below
their respective SLs

PFOS was detected above the SL at AOI02-02 at a concentration of 4.4 J ng/L and below the SL
at AOI02-01 and AASF-01 at concentrations of 2.2 J- ng/L and 3.0 J- ng/L, respectively. PFBS,
PFHxS, and PFOA were detected at concentrations below their respective SLs at AOI02-01,
AOI02-02, and AASF-01. All three locations (AOI02-01, AOI02-02, and AASF-01) had
detections of PFBS at concentrations ranging from 1.1 J ng/L to 1.7 J- ng/L. All three locations
(AOI02-01, AOI02-02, and AASF-01) had detections of PFHxS at concentrations ranging from
4.1 ng/L to 4.5 ng/L. All three locations (AOI02-01, AOI02-02, and AASF-01) had detections of
PFOA at concentrations ranging from 3.0 J- ng/L to 3.8 ng/L. PFNA was not detected in the
groundwater samples.

6.4.3, AOI 2 Conclusions

Based on the results of the SI, PFNA, PFOS, and PFOA were detected in surface soil below their
respective SLs. PFOS was detected in groundwater at a concentration above the SL, and PFBS,
PFHxS, and PFOA were detected in groundwater at concentrations below their respective SLs.
Since PFOS was detected at the SL near the upgradient boundary at AASF-02, the exceedance of
PFOS in groundwater at AOI 2 may be the result of a source unrelated to DoD activities. As the
contamination present is not likely the result of DoD activities, no further action by ARNG is
warranted at AOI 2.

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Site Inspection Report
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5.7 LABORATORY ANALYTICAL METHODS

Samples were analyzed by LC/MS/MS, compliant with QSM Version 5.3 Table B-15, at
Eurofins in Lancaster, Pennsylvania, a DoD ELAP and NELAP-certified laboratory.

One soil sample per AOI was also analyzed for TOC using EPA Method 9060A, pH by EPA
Method 9045D, and grain size using ASTM Method D-422.

5.8 Deviations from SI UFP-QAPP Addendum

Deviations from the UFP-QAPP Addendum occurred based on conditions encountered during
field activities. Deviations from the UFP-QAPP Addendum are noted below:

Refusal was encountered at AASF-02a, AASF-02b, and AOI01-02 using a hollow-stem
auger drilling approach after encountering difficult lithology and interbedded layers of
caliche. The drilling method was changed to a rotosonic drilling method to penetrate the
lithology observed during the first three boring attempts. No soil samples were submitted
for analysis from the hollow-stem auger attempts. The hollow-stem auger borings were
abandoned with Portland cement. The change in drilling technology was discussed
between EA/Wood, ARNG, and USACE. The Field Change Request Form is included in
Appendix B-4.

Shaker tests on groundwater samples were not performed during groundwater sampling
due to human error (field team omission). The purpose of Shaker tests is to provide the

laboratory with advance notice of samples that foam with agitation. The laboratory did

not indicate any issue with foaming during the groundwater sample analyses; therefore,
data quality was not impacted by the Shaker tests omission.

Equipment blanks were collected off each type of sampling equipment (steel mixing
bowl, hand auger, and groundwater sampling pump) but not on each day of usage. All
non-dedicated sampling equipment was decontaminated prior to use and following usage.
Equipment blanks were collected after sample collection was complete and the non-
dedicated field equipment had been decontaminated. The field team did not complete the
equipment blank per piece of equipment per day as outlined in the SI UFP-QAPP
Addendum (EA/Wood, 2022a). The available blank sample data was non-detect for target
analytes which suggests proper decontamination of non-dedicated field equipment and
field quality control procedures occurred before each sampling commenced but cannot be
verified.

EA Engineering, Science, and Technology, Inc., PBC 5-6


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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

LIST OF APPENDICES

Appendix A. Data Usability Assessment and Validation Reports
Appendix B. Field Documentation

B1. Log of Daily Notice of Field Activities

B2. Sampling Forms

B3. Survey Data

B4. Field Change Request Form

BS. Investigation-Derived Waste Polygons
Appendix C. Photographic Log
Appendix D. Technical Project Planning Meeting Minutes
Appendix E. Boring Logs and Well Construction Diagrams
Appendix F. Analytical Results
Appendix G. Laboratory Reports

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Site Inspection Report
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7141 AOT1

AOI | includes the hangars and helipad where AFFF has been stored on a Tri-MaxTM hand truck
fire extinguisher and a fire extinguisher stored just outside of Hangar | and 2, near the helipad
area. No potential releases or AFFF usage were noted during the PA (AECOM, 2020) at AOI 1.

No relevant compounds (PFOA, PFOS, PFHxS, PFNA, and PFBS) were detected in surface and
subsurface soils at AOI 1. Therefore, the surface soil exposure pathways for site workers,
construction workers, residents, and trespassers are incomplete. The CSM for AOI 1 is presented
on Figure 7-1.

7.1.2 AOI2

AOI 2 includes the possible FTA adjacent to the Helipad Area where a possible AFFF fire
extinguisher discharge could have occurred as part of a training activity based on anecdotal
knowledge. Because details are not specifically recalled, this training event is considered a
potential AFFF release as noted in the PA (AECOM, 2020) at AOI 2.

PFOA, PFOS, and PFNA were detected in surface soils at AOI 2. Site workers and construction
workers could contact constituents in surface soil via incidental ingestion and inhalation of dust.
Therefore, the surface soil exposure pathways for inhalation of dust and ingestion of soil by site
workers and construction workers are potentially complete. AOI 2 is located within a controlled
area of Airport property; therefore, the surface soil exposure pathway for residents and
trespassers are incomplete. No relevant compounds (PFOA, PFOS, PFHxS, PFNA, and PFBS)
were detected in subsurface soil at AOI 2; therefore, the subsurface soil exposure pathway for
site workers, construction workers, residents, and trespassers is incomplete. The CSM is
presented in 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 at each AOI based on the aforementioned
criteria.

7.21 AOI1

PFOS was detected in groundwater at a concentration equal to the SL in one groundwater sample
at AOI 1 and below the SL in the other two samples. PFOA, PFBS and PFHxS were detected
below their respective SLs in groundwater samples collected at AOI 1. The City of North Las
Vegas supplies potable water to the Facility and surrounding area. The source of the city’s water
supply is primarily Lake Mead but also groundwater. There are municipal and domestic wells
within a 4-mile radius of the Facility. Therefore, the pathway for exposure to site workers and
offsite residents via ingestion of groundwater is considered potentially complete. Static depths to
water measured at AOI | in February 2023 during the SI ranged from 32.86 to 33.91 ft bgs.
Construction workers are unlikely to encounter groundwater due to its depth; therefore, the
ingestion exposure pathway for future construction workers is considered incomplete. AOI 1 is
located within a controlled area of Airport property; therefore, the groundwater exposure

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Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

7. EXPOSURE PATHWAYS

The Conceptual Site Model (CSM) for each AOI, revised based on the SI findings, is 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 Facility 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:

Contaminant source;
Environmental fate and transport;
Exposure point;

Exposure route; and

Potentially exposed populations.

Sw Ge

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 no identified complete
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 the relevant compounds above the SLs. Areas with an identified potentially
complete pathway and a complete pathway 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 EPA guidance for risk screening (EPA 2001).
Potential receptors at the Facility include site workers (e.g., facility staff and visitors, staff and
visitors at the adjoining Cheyenne Air Center services, and visiting soldiers), construction
workers, trespassers, recreational users outside the Facility boundary. No recreational areas are
located within 10 miles of the Facility and a recreational user is unlikely but was still included in
the assessment.

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 each AOI based on the aforementioned criteria.

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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

7.3.2 AOL2

There were no documented releases of PFAS to the ground surface at the possible FTA, but
PFAS-containing fire suppressants were stored at the Facility, and there is anecdotal knowledge
indicating a possible fire extinguisher discharge with a potential for PFAS release to have
occurred at AOI 2 and migrated to the airport’s stormwater system. PFOS, PFOA, and PFNA
were detected in the surface soil below SLs at AOI 2. It is possible these compounds could be
transported from soil to surface water and sediment via runoff and conveyance in the stormwater
system. Stormwater from AOI 2 is conveyed to the southeast and discharges into an open
drainage channel located on the North Las Vegas Airport approximately 0.2 miles to the south of
the Facility. Surface water in the open drainage channel flows to the east then south, eventually
discharging to the Carey Avenue/Lake Mead detention pond that is located on Airport property
approximately 1.5 miles to the southeast of the Facility. The detention pond discharges into the
City of North Las Vegas storm water system.

The exposure pathway for incidental ingestion of surface water and sediment by site workers,
construction workers, and residents is considered potentially complete. Access to the North Las
Vegas Airport, including the detention pond, is controlled; therefore, the surface water and
sediment ingestion exposure pathway for trespassers are considered incomplete. The CSM is
presented in Figure 7-2.

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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

4. PROJECT DATA QUALITY OBJECTIVES

As identified during the Data Quality Objective (DQO) process and outlined in the SI Uniform
Federal Policy (UFP)-Quality Assurance Project Plan (QAPP) Addendum (EA/Wood, 2022a),
the objective of the SI is to identify whether there has been a release to the environment at the
AOlIs 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 the 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 for the SI include the following:

e The PA Report for Cheyenne AASF (AECOM, 2020);

e Analytical data from groundwater and soil samples collected as part of this SI in
accordance with the site-specific UFP -QAPP Addendum (Wood 2022a);

e 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 vertically by the depth of temporary monitoring wells installed
within groundwater where encountered (maximum depth of 37 feet bgs). Off-Facility sampling
was included in the scope of this SI (Figures 2-1 and 2-2). ARNG obtained right-of-entry from
the Cheyenne Air Center. WSP obtained a temporary permit for geotechnical investigations from
the Clark County Department of Aviation with consent by the Cheyenne Air Center. The right-
of-entry and temporary permit established limits that bound the horizontal extent of the SI.

If future off-Facility sampling is required, the proper stakeholders will be notified, and necessary
temporary permits and rights of entry for geotechnical investigation will be obtained by ARNG
with property owner(s). Temporal boundaries were limited to the earliest available time field
resources were available to complete the study.

44 ANALYTICAL APPROACH

Samples were analyzed by Eurofins, accredited under the DoD Environmental Laboratory
Accreditation Program (DoD ELAP; Accreditation Number 1.01) and the National
Environmental Laboratory Accreditation Program (NELAP; Certificate Number 021). Data were
compared to applicable SLs within this document and decision rules as defined in the UFP-
QAPP Addendum (EA/Wood, 2022a).

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Army National Guard Site Inspections -—
Site Inspection Report |
Cheyenne Army Aviation Support Facility
Las Vegas, Nevada

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Army National Guard Site Inspections
Site Inspection Report
Cheyenne Army Aviation Support Facility
Las Vegas, Nevada

Figure 2-4
Groundwater Elevations

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(0.5 ft interval, ft. amsl)

Dates.
Prepared By:...
Prepared F



Army National Guard Site Inspections
Site Inspection Report
Cheyenne Army Aviation Support Facility
Las Vegas, Nevada

Figure 2-2
Facility Topography

Cheyenne Army
— Aviation Support
Facility

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Kenner Dt

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Facility Data
[om] Cheyenne Air Center Boundary
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Data Sources: ESRI 2020, AECOM 2020

Date:
Prepared By:...
Prepared For

May 2023
WPS,
USACE



Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

4.55 DATA USABILITY ASSESSMENT

The Data Usability Assessment (DUA), which is provided in Appendix A, is an evaluation at the
conclusion of data collection activities that uses the results of both data verification and
validation in the context of the overall project decisions or objectives. Using both quantitative
and qualitative methods, the assessment determines whether project execution and the resulting
data have met 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 UFP-QAPP (EA, 2020a).

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2.2.4 Climate

The Facility lies in a relatively high-altitude portion of the Mojave Desert, with a subtropical hot-
desert climate. Summers display classic desert southwest characteristics with low humidity and
daily high temperatures typically exceeding 100 degrees Fahrenheit (°F) and lows around 70 °F.
Winters are mostly mild. The Las Vegas region generally receives less than 5 inches of rainfall
per year.

2.2.5 Current and Future Land Use

Presently, Cheyenne AASF resides in Cheyenne Air Center. The AASF includes a portion of a
large building (Hangars 1 and 2 including an office area), and utilizes three helicopter landing
pads and a small, paved area. NVARNG leases Hangar 1 and Hangar 2, including an office
space, in a portion of a large building shared with other tenants. The NVARNG lease is through
September 2023 but is anticipated to be renewed. NVARNG’s lease agreement does not include
the helipad and the paved areas within the Cheyenne Air Center. NVARNG’s access to these
areas is informally managed directly with the property owner. The current land use is zoned as
M-2 General Industrial. The Cheyenne Air Center and the North Las Vegas Airport have
controlled access. Future land use is not anticipated to change, subject to lease renewals to the
properties.

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 species are listed as federally endangered, threatened, proposed, and/or candidate
species in Clark County, NV (U.S. Fish and Wildlife Services, 2021):
Birds:

Yellow-billed Cuckoo, Coccyzus Americanus (threatened)

Southwestern Willow Flycatcher, Empidonax Traillii Extimus (endangered)
California Least Tern, Sterna Antillarum Browni (endangered)

Yuma Ridgway’s Rail, Ra/lus Obsoletus Yumanensis (endangered)

Fishes:

Woundfin, Plagopterus Argentissimus (endangered)

Virgin River Chub, Gila Seminuda (endangered)

Humpback Chub, Gila Cypha (threatened)

Bonytail Chub, Gila Elegans (endangered)

Big Spring Spinedace, Lepidomeda Mollispinis Pratensis (threatened)

Moapa Dace, Moapa Coriacea (endangered)

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Site Inspection Report
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pathway for trespassers is considered incomplete. The CSM for AOI 1 is presented on
Figure 7- 1.

7.2.2 AOI2

PFOS was detected above the SL in one groundwater sample at AO] 2 and below the SL in the
other two groundwater samples. PFOA, PFOS, PFBS and PFHxS were detected below their
respective SLs in groundwater samples collected at AOI 2. The City of North Las Vegas supplies
potable water to the Facility and surrounding area. The source of the city’s water supply is
primarily Lake Mead but also groundwater. There are municipal and domestic wells within a 4-

mile radius of the Facility. Therefore, the pathway for exposure to site workers and offsite
residents via ingestion of groundwater is considered potentially complete. Static depths to water
measured at AO] 2 in February 2023 during the SI ranged from 29.90 to 34.45 ft bgs.
Construction workers are unlikely to encounter groundwater due to its depth; therefore, the
ingestion exposure pathway for future construction workers is considered incomplete. AOI 2 is
located within a controlled area of Airport property; therefore, the groundwater ingestion
pathway for trespassers is incomplete. The CSM for AOI 2 is presented on Figure 7-2.

7.3. SURFACE WATER AND SEDIMENT EXPOSURE PATHWAY

Stormwater from the areas of AOI 1 and AOI 2 flows toward the storm drain adjacent to AOI 2
then is conveyed via the Airport stormwater system. Stormwater inlets are also located to the
north of the Facility on Cheyenne Avenue. The City of North Las Vegas storm water drainage
system conveys stormwater runoff into the Las Vegas Wash and its tributaries. SI results for soil
and groundwater from AOI 1 and AOI 2, 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. No surface water or sediment samples were
collected as part of the SI.

PFAS are water soluble and can migrate readily via leaching and run-off. Because PFNA, PFOS,
and PFOA were detected in soil at AOI 2 and PFOA, PFOS, PFHxS, and PFBS were detected in
groundwater at AOI 1 and AOI 2, it is possible that those compounds may have migrated from
soil and/or groundwater to surface water via stormwater discharge.

7.3.1 AOI1

There were no documented releases of PFAS to the ground surface at the Hangars or helipad
area, but PFAS-containing fire suppressants were stored at the Facility, and there is the potential
for PFAS releases inside and immediately surrounding the Facility. The hangars do not have
floor drains or connection to the city sewer. There are no documented incidents of PFAS-
containing (or potentially containing) fire suppressants being discharged to the stormwater
system. No relevant compounds were detected in the surface soil at AOI 1 so exposure pathways
via runoff are considered incomplete. Therefore, the surface water and sediment ingestion
exposure pathways for site workers, construction workers, residents, trespassers, and recreational
users are considered incomplete. The CSM is presented in Figure 7-1.

EA Engineering, Science, and Technology, Inc., PBC 7-3


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Site Inspection Report

Cheyenne Army Aviation Support Facility, Nevada Version: FINAL
USDA U.S. Department of Agriculture

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

Wood Wood Environment & Infrastructure Solutions, Inc.

WsP WSP USA Environment & Infrastructure Inc.

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Site Inspection Report
Cheyenne Army Aviation Support Facility
Las Vegas, Nevada

Figure 3-1
Areas of Interest

Trimax.
__ Storage

Facility Data Hydrology/Hydrogeology Data Sources: ESRI 2020, AECOM 2019
Area of Interest (AO!) River/Stream
CC) Helipaa

Facility Boundary

=] Cheyenne Air Center Boundary "
- Prepared By

[2] Potential PFAS Release (Off-Facility) Prepared By:

May 2023
...WPS
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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

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EA Engineering, Science, and Technology, Inc., PBC 2-16


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Site Inspection Report

Cheyenne Army Aviation Support Facility, Nevada Version: FINAL
LIST OF TABLES

Table ES-0-1 Screening Levels (Soil and Groundwater).........::ccssessessessessesseesssneseesesseeseeseeseenees 2

Table ES-0-2. Summary of Site Inspection Findings and Recommendations .......:.:sesessseseeees 2

Table 5-1 Site Inspection Samples by Medium Cheyenne Army Aviation Support Facility,
Deis: Vegas, Nevade iscsicisissccetsseissaish isd cvaseisjutssszas sett sanietsaiateiacsedinaaseysstesdvbanady 5-7

Table 5-2 Soil Boring Depths and Temporary Well Screen Intervals Cheyenne Army
Aviation Support Facility, Las Vegas, Nevada.

Table 5-3 Groundwater Elevation Cheyenne Army Aviation Support Facility, Las Vegas,
Nevada...

Table 6-1 Screening Levels (Soil and Groundwater).............sssssssscsssecesessecrsseaeceeseeeeneneene 6-1

Table 6-2 PFOA, PFOS, PFBS, PFNA, and PFHxS Results in Surface Soil, Site
Inspection Report, Cheyenne Army Aviation Support Facility... 6-5

Table 6-3 PFOA, PFOS, PFBS, PFNA, and PFHxS Results in Shallow Subsurface Soil,
Site Inspection Report, Cheyenne Army Aviation Support Facility ................6-7

Table 6-4 PFOA, PFOS, PFBS, PFNA, and PFHxS Results in Deep Subsurface Soil, Site
Inspection Report, Cheyenne Army Aviation Support Facility...........0sese 6-9

Table 6-5 PFOA, PFOS, PFBS, PFNA, and PFHxS Results in Groundwater, Site
Inspection Report, Cheyenne Army Aviation Support Facility........0..s0000 6-11

Table 8-1 Summary of Site Inspection Findings and Recommendations ............eeee 8-3

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Site Inspection Report

Cheyenne Army Aviation Support Facility, Nevada Version: FINAL
LIST OF FIGURES
Figure 2-1 Facility Location sicccscsssssasascstsszsseesetetersecetersecssascsastctessesnscoasscstenseassdetesapcisbetagie 2-7
Figure 2-2 Pacility: Topography isiisckiessiicedesssisscouscciesccasietsscedncossvcadsovtascuaucseutbiaveniesssdetaasse 2-9
Figure 2-3 GOUT WAREE REREATES J. 0u5o1eseessesssccsesnceaesensxanssresenssenvessnvassqsneasescssnascvenscasscouss 2-11
Figure 2-4 Groundwater Elevations ............ssssssssssscsesssessesssesssessesssesssesssessesessssesssseseenneens 2-13
Figure 2-5 Surface Water Features...
Figure 3-1 Areas: Of Intenestissssisscssiccssscsisssadsecadacssdscaivessacestsssstsacssncessecpiessins wtasaatscstysszetestees 3-3
Figure 5-1 Site Inspection Sample Locations.
Figure 6-1 PFOA: Detections in Soil ssisis.cassscasicsssscasscsidscsssssasicsasscasncstinccbtesasicstessotecttisoee 6-13
Figure 6-2 PFOS Detections in Soil sscsicssssssssssssossessssssssssossesasssossesaseosssossssosesansasosnseaisionsn 6-15
Figure 6-3 PRBS Detechons 20 SOIL 2.scrc:catesscjeesttsce sasessecsjoaseneregtecsinssatneteceateaetehemeateesed 6-17
Figure 6-4 PFHXS Detections in Soi]... eeceseseeseseesesessssesessesessceesesncsesnsacsesncaeseneseanens 6-19
Figure 6-5 PFNA Detections:in Soil <..::..cccssscsscsssestessesnesnsssecsecasnvsassceabeanssosssesseszesessostasese 6-21
Figure 6-6 PFOA, PFOS, and PFBS Detections in Groundwater ............:.ccccssseseseseeseee 6-23
Figure 6-7 PFHxS and PFNA Detections in Groundwater..
Figure 7-1 Conceptual Site Model, AQ Ws: 5 sz. cascccsssa ke iiss ates esas ads dasecegseassesszecosessoezanacsen 7-5
Figure 7-2 Conceptual Site Model, AOI 2

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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

Pahrump Poolfish, Empetrichthys Latos (endangered)

Devil’s Hole Pupfish, Cyprinodon Diabolis (endangered)

Razorback Sucker, Xyrauchen Texanus (endangered)

Flowering Plants:

White Margined Beardtongue, Penstemon Albomarginatus (threatened)
Pahrump Valley Buckwheat, Eriogonum Bifurcatum (threatened)

Las Vegas Bearpoppy, Arctomecon Californica (threatened)
Threecorner Milkvetch, Astragalus Geyeril Var. Triquetrus (threatened)
Death Valley Beardtongue, Penstemon Fruiticiformis Ssp. Amargosae (threatened)
Sticky Buckwheat, Eriogonum Viscidulum (threatened)

Rough Angelica, Angelica Scabrida (threatened)

Insects:

Monarch Butterfly, Danaus Plexippus (candidate)

Mt. Charleston Blue, Plebejus Shasta Charlestonensis (endangered)
Reptiles:

Mojave Desert Tortoise, Gopherus Agassizii (threatened)

2.3 HISTORY OF PFAS USE

One AOI, subsequently divided into two AOIs for project management purposes for the SI, was
identified in the PA where aqueous film forming foam (AFFF) may have been used, stored,
disposed, or released historically at the Cheyenne AASF (AECOM, 2020). Interviews and
records obtained during the PA indicate that NVARNG formerly housed a single Tri-MaxTM
hand-truck fire extinguisher in Hangar 2, and presently, one fire extinguisher containing AFFF is
stored just outside of Hangars | and 2, near the helipad area. The hangars and helipad area are
identified as AOI 1. AOI 2 is the area outside of the helipad area, which was identified as a
possible fire training area (FTA) in the PA. A description of each AOI is presented in Section 3.

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Site Inspection Report
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Version: FINAL

IDW
ITRC

LC/MS/MS
LCS

LCSD
LOQ
LVVWD

MIL-SPEC
MS
MSD

NDEP
NELAP
ng/L

No.

NV
NVARNG

OSD

PA
PFAS
PFBS
PFHxS
PFNA
PFOA
PFOS
PID
PVC

QA
QAPP
Qc
QSM

RI
RPD

SI
SL
TOC
TPP

UFP
USACE

Investigation-derived waste
Interstate Technology Regulatory Council

Liquid chromatography tandem mass spectrometry
Laboratory control sample

Laboratory control sample duplicate

Limit of quantification

Las Vegas Valley Water District

military specification
Matrix spike
Matrix spike duplicate

Nevada Division of Environmental Protection

National Environmental Laboratory Accreditation Program
Nanogram(s) per liter

Number

Nevada

Nevada Army National Guard

Office of the Secretary of Defense

preliminary assessment

per- and polyfluoroalkyl substances
perfluorobutanesulfonic acid
perfluorohexanesulfonic acid
perfluorononanoic acid
perfluorooctanoic acid
perfluorooctanesulfonic acid
photoionization detector

polyvinyl chloride

Quality assurance

Quality Assurance Project Plan
Quality control

Quality Systems Manual

Remedial investigation
Relative percent difference

Site Inspection

Screening level

Total organic carbon
Technical Project Planning

Uniform Federal Policy
U.S. Army Corps of Engineers

EA Engineering, Science, and Technology, Inc., PBC

vii


Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

e No relevant compounds (PFOS, PFOA, PFBS, PFNA, and PFHxS) were detected in surface,
shallow subsurface, or deep subsurface soil at AOI 1.

e PFOS, PFOA, PFBS, and PFHxS were detected in groundwater below their respective SLs at
AOI | and at the upgradient Facility boundary at AASF-02. PFHxS, PFOS, and PFOA
concentrations were slightly higher at the upgradient Facility boundary than at AOI 1. The
concentration of 4.0 ng/L of PFOS at AASF-02 is equal to the SL for PFOS in groundwater.

e Based on the results of the SI, no further evaluation of AOI 1 is warranted in the RI.

At AOI 2:

e PFOA, PFOS, and PFNA was detected in surface soil at AOI 2 at concentrations two orders
of magnitude below their respective SLs. No relevant compounds were detected in shallow
and deep subsurface soil samples.

e PFOS, PFOA, PFBS, and PFHxS were detected in groundwater at AOI 2 and in the
upgradient sample at AASF-01. Concentrations of PFHxS and PFOA were slightly higher at
the upgradient Facility boundary than at AOI 2, while PFBS and PFOS concentrations were
slightly higher at AOI 2 than at the upgradient boundary. PFOS exceeded the SL in
groundwater at AOI 2 in temporary well, AOI02-02 with a concentration of 4.4 J ng/L.
Detections of PFOA, PFHxS, and PFBS did not exceed their respective SLs in all AOI 2 and
AASF-01 groundwater samples.

e Based on the results of the SI, further evaluation of AOI 2 may be warranted due to an
exceedance of the PFOS groundwater SL. However, the contamination present is not likely
the result of DoD activities, and no further action by ARNG is warranted at this time.

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.

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9, REFERENCES

AECOM. 2020. Final Preliminary Assessment Report, Cheyenne Army Aviation Support
Facility, Las Vegas, Nevada. July.

Assistant Secretary of Defense. 2022. Investigating Per- and Polyfluoroalkyl Substances within
the Department of Defense Cleanup Program. United States Department of Defense.
July.

Department of the Army (DA). 2016a. EM-200-1-2, Environmental Quality, Technical Project
Planning Process. 29 February.

. 2016b. Army Guidance to Address Perfluorooctane Sulfonate (PFOS) and
Perfluorooctanoic Acid (PFOA) Contamination. August.

. 2018. Army Guidance for Addressing Releases of Per-and Polyfluoroalkyl Substances.
September.

DoD. 2019a. Department of Defense (DoD), Department of Energy (DOE) Consolidated Quality
Systems Manual (OSM) for Environmenial Laboratories, Version 5.3. May.

. 2019b. General Data Validation Guidelines. November.

. 2020. Data Validation Guidelines Module 3: Data Validation Procedure for Per- and
Polyfluoroalkyl Substances Analysis by QSM Table B-15. May.

EA, Engineering, Science, and Technology, PBC (EA). 2020a. Final Programmatic Uniform
Federal Policy Quality Assurance Project Plan, Site Inspections for Per- and
Polyfluoroalkyl Substances Impacted Sites, ARNG Installations, Nationwide. December.

. 2020b. Accident Prevention Plan, Programmatic Uniform Federal Policy Quality
Assurance Project Plan, Site Inspections for Per- and Polyfluoroalkyl Substances
Impacted Sites, ARNG Installations, Nationwide, Revision 1. November.

EA Engineering, Science, and Technology, PBC and Wood Environment & Infrastructure
Solutions, Inc. (EA/Wood). 2022a. Final Site Inspection Uniform Federal Policy Quality
Assurance Project Plan (UFP-QAPP) Addendum, Cheyenne Army Aviation Support
Facility (AASF). Las Vegas, Nevada, Per- and Polyfluoroalkyl Substances Impacted
Sites, ARNG Installations, Nationwide. March.

. 2022b. Accident Prevention Plan/Site Safety and Health Plan Addendum, Site
Inspections for Per- and Polyfluoroalkyl Substances Impacted Sites, ARNG Installations,
Nationwide Cheyenne Army Aviation Support Facility (AASF). Las Vegas, Nevada.
November.

Guelfo, J.L. and C.P. Higgins. 2013. Subsurface transport potential of perfluoroalkyl acids and
aqueous film-forming foam (AFFF)-impacted sites. Environmental Science and
Technology 47(9):4164-71.

EA Engineering, Science, and Technology, Inc., PBC 9-1


Army National Guard Site Inspections
Site Inspection Report
Cheyenne Army Aviation Support Facility NV
Las Vegas, Nevada
Figure 2-3
Groundwater Features
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Flow Direction @ Irrigation Propered 8



FINAL

Site Inspection Report

Cheyenne Army Aviation Support Facility
(AASF)

Las Vegas, Nevada

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

December 2023

Prepared for:

Army National Guard Headquarters
111 S. George Mason Drive
Arlington, VA 22204

UNCLASSIFIED


Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

Higgins, C.P., and R.G. Luthy. 2006. Sorption of perfluorinated surfactants on sediments.
Environmental Science and Technology 40 (23): 7251-7256.

ITRC. 2018. Environmental Fate and Transport for Per- and Polyfluoroalkyl Substances.
March.

U.S. Environmental Protection Agency (EPA). 1980. Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA). 11 December.

. 1994. National Oil and Hazardous Substances Pollution Contingency Plan (Final Rule).
40 Code of Federal Regulations Part 300; 59 Federal Register 47384. September.

. 2001. Risk Assessment Guidance for Superfund, Volume I: Human Health Evaluation
Manual (Part D, Standardized Planning, Reporting, and Review of Superfund Risk
Assessments). December.

. 2005. Federal Facilities Remedial Site Inspection Summary Guide. July.

. 2006. Guidance on Systematic Planning Using the Data Quality Objectives Process
USEPA/240/B-06/001. February.

. 2017. National Functional Guidelines for Organic Superfund Data Review. OLEM
9355.0-136, EPA-540-R-2017-002. Office of Superfund Remediation and Technology
Innovation. January.

U.S. Fish and Wildlife Service (USFWS). 2021. Endangered Species. http://ecos.fws.gov/ipac/.
Accessed 21 April.

Xiao, F., M. F. Simcik, T.R. Halbach, and J.S Gulliver. 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.

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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada

Version: FINAL

SI sampling results from the two AOIs were compared to OSD SLs. Table ES-2 summarizes the
SI results for each AOI. Based on the results of this SI, and following the CERCLA process, no
further action is warranted under CERCLA for AOI 1 and AOI 2.

Table ES-1 Screening Levels (Soil and Groundwater)

bgs =

Abbreviations:
ug/kg = microgram(s) per kilogram

below ground surface

ng/L = nanogram(s) per liter

Residential Industrial / Commercial
(Soil) Composite Worker (Soil) Tap Water
(ug/kg)' i (Groundwater)
Analyte” (0-2 feet bgs) (2-15 feet bgs) (ng/L)!
PFOA 19 250 6
PFOS 13 160 4
PFBS 1,900 25,000 601
PFHxS 130 1,600 39
PFNA 19 250 6
|Notes:

1. Assistant Secretary of Defense. July 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. May 2022.

2. 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

( } = Detected; exceedance of screening levels

3) = Detected; no exceedance of screening levels

O =Not detected
*PFOS was equal to the SL in the groundwater sample collected upgradient of the Facility and marginally

exceeded the SL in one monitoring well at AOI 2. As the contamination present is not likely the result of
DoD activities, no further action by ARNG is warranted at AOI 2.

AOI Potential Release Soil — Groundwater —| Groundwater - Future Action
Area Source Area | Source Area |Facility Boundary)
I Risngart snd) Helipad O © © No further action
3 Possible sts Testing © t © No further action*
Legend:

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ES-2


Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

EXECUTIVE SUMMARY

The Army National Guard (ARNG) G-9 is performing Preliminary Assessments (PAs) and Site
Inspections (SIs) at ARNG facilities nationwide based on the current or potential historical use of
per- and polyfluoroalkyl substances (PFAS) with a focus on the six compounds presented in the
memorandum regarding Investigating Per- and Polyfluoroalky! Substances within the
Department of Defense (DoD) Cleanup Program (Assistant Secretary of Defense, 2022) from the
Office of the Secretary of Defense (OSD) dated 6 July 2022. The six compounds listed in the
OSD memorandum include perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid
(PFOA), perfluorobutanesulfonic acid (PFBS), perfluorononanoic acid (PFNA),
perfluorohexanesulfonic acid (PFHxS), and hexafluoropropylene oxide dimer acid (HFPO-DA)!.
These compounds are collectively referred to as “relevant compounds” throughout the document,
and the applicable screening levels (SLs) are provided below in Table ES-1.

The PA identified one Area of Interest (AOT) where PFAS-containing materials may have been
used, stored, disposed, or released historically, and the AOI was subsequently divided into two
AOIs for the SI (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 and determine
whether further investigation is warranted, a removal action is required to address immediate
threats, or no further action is required based on SLs for the relevant compounds. This SI was
completed at the Cheyenne Army Aviation Support Facility (AASF) in Las Vegas, Nevada and
determined that no further evaluation by the DoD (ARNG G-9) under the Comprehensive
Environmental Response, Compensation, and Liability Act (CERCLA) is warranted for AOI 1:
Hangars and Helipad and AOI 2: Possible Fire Training Area (FTA) at this time. The Cheyenne
AASF will also be referred to as the “Facility” throughout this document.

The Facility, operated by Nevada ARNG (NVARNG), leases approximately 0.4 acre of hangar
space, Hangar | and 2, from the Cheyenne Air Center that is located on the north edge of the
North Las Vegas Airport in North Las Vegas, Nevada. The Cheyenne Air Center is a privately-
owned company servicing private airplanes, as well as some aviation tour companies. NVARNG
leases hangar space for the AASF, Hangar | and Hangar 2, and office space in a portion of a
large building shared with other tenants. Hangar | is leased to the Rochelle Aizenberg Revocable
Trust and then, starting in 2018, subleased to the NVARNG. Hangar 2 is leased to NVARNG by
a private owner per a 2018 agreement (AECOM, 2020). A possible fire training area (FTA) is
located to the southwest of the Cheyenne Air Center within the North Las Vegas Airport
property (EA/Wood, 2022a). The North Las Vegas Airport opened in 1941 covering 920 acres.

' 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 S$]. 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.

EA Engineering, Science, and Technology, Inc., PBC ES-1


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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

ASTM = American Society for Testing and Materials

bgs = below ground surface

EB = equipment rinsate blank

FD = field duplicate

FB = 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

EA Engineering, Science, and Technology, Inc., PBC 5-8



Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada

Version: FINAL
Table 8-1 Summary of Site Inspection Findings and Recommendations
Potential Release Soil — Groundwater —| Groundwater — 2
AO! Area Source Area | Source Area |Facility Boundary eat
1 Pinger ene Helin’ O © © No further action
2 Possible FTA © @ © No further action*
Legend:

[ } = Detected; exceedance of screening levels

(3) = Detected; no exceedance of screening levels
O = Not detected

*PFOS was equal to the SL in the groundwater sample collected upgradient of the Facility and marginally

exceeded the SL in one monitoring well at AOI 2. As the contamination present is not likely the result of
DoD activities, no further action by ARNG is warranted at AOI 2.

EA Engineering, Science, and Technology, Inc., PBC

8-3


Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

3.3.1 North Las Vegas Airport

The North Las Vegas Airport opened in 1941 covering 920 acres with three asphalt runways.
The Cheyenne AASF is located adjacent to the North Las Vegas Airport property, and AOI 2 is
located within the North Las Vegas Airport boundary (EA/Wood, 2022a). The North Las Vegas
Airport runways are located to the south of the Facility. There have been three crashes that
occurred at the North Las Vegas Airport throughout its history, though it is unknown whether
AFFF was used as an emergency response measure for these incidents (AECOM, 2020). The
most recent incident occurred in July 2022 with a two single-engine aircraft collision. The
locations of these crashes are interpreted to be downgradient of the Facility, and are not expected
to impact PFAS concentrations in the groundwater underlying the Facility. No other potential
AFFF releases on the Airport property were identified but general AFFF usage at airports can
include occasional nozzle tests and fire training that may have occurred at unknown locations.

No other off-Facility source areas were identified in the PA Report or during the SI.

EA Engineering, Science, and Technology, Inc., PBC 3-2


Site Inspection Report

Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

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 and Table 6-1. A discussion of the results for each AOI is provided in
Sections 6.3 and 6.4. Tables 6-2 through 6-6 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 (Assistant Secretary
of Defense 2022). The ARNG program under which this SI was performed follows this DoD
policy. Should the maximum concentration for sampled media exceed the SLs established in the
OSD memorandum, the AOI may proceed to the next phase under CERCLA. The SLs
established in the OSD memorandum apply to the five compounds presented on Table 6-1.

Table 6-1 Screening Levels (Soil and Groundwater)

Residential Industrial / Commercial
(Soil) ‘Composite Worker Tap Water
Analyte? (uglkg)! (Soil) (Groundwater)
ees (ug /kg)! (ng/L)!
2-15 ft bgs
PFOA 19 250 6
PFOS 13 160 4
PFBS 1,900 25,000 601
PFHxS 130 1,600 39
PFNA 19 250 6
Notes:

1. Assistant Secretary of Defense. July 2022. Risk Based Screening Levels in Groundwater and Soil using
U.S. Environmental Protection Agency’s (EPA’s) Regional Screening Level Calculator. Hazard Quotient
(HQ)=0.1. May 2022.

2. 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.

Abbreviations:

g/kg = microgram(s) per kilogram
bgs = below ground surface

ft= feet

ng/L = nanogran(s) per liter

The data in the subsequent sections are compared against the SLs presented in Table 6-1. The
SLs for groundwater are based on direct ingestion. The SLs for soil are based on incidental
ingestion and are applied to the depth intervals reasonably anticipated to be encountered by the
receptors identified at the Facility: the residential scenario is applied to surface soil results (0 to 2
ft bgs) and the industrial/commercial worker scenario is applied to shallow subsurface soil

EA Engineering, Science, and Technology, Inc., PBC 6-1


Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

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, one potential release area was identified at
Cheyenne AASF and later divided into 2 AOIs identified as: AOI 1 - Hangars and Helipad Area
and AOI 2 - Possible FTA. The AOIs are shown on Figure 3-1.

3.1 AOI1—HANGARS AND HELIPAD AREA

AOI | is located in the west portion of Cheyenne Air Center. AOI 1 encompasses the hangars
where a Tri-MaxTM hand truck fire extinguisher was stored for approximately 16 years, and the
location where a AFFF fire extinguisher is currently kept.

Hangar 2 formerly housed a single Tri-Max'TM hand-truck fire extinguisher that was stored in
various locations around the structure. This Tri-MaxTM unit was on the Facility from the early
2000s until 2016, when it was sent back to the Carson City Warehouse Defense Reutilization and
Marketing Office. The unit was regularly serviced by a safety officer in Reno contracted through
ABC until sometime between 2008 and 2010. According to interviews, there are no records or
recollection of the hand-truck ever being used for fire training or emergency response.

Presently, one fire extinguisher containing AFFF exists on the Facility. The extinguisher is
regularly inspected and maintained, and it is in good condition. According to personnel
interviews, the unit is stored just outside of Hangar | and 2, near the helipad area. The fire
suppression system in Hangar 2 was installed prior to NVARNG’s lease. The fire suppression
system utilizes water and is tested quarterly. If a release were to have occurred, the release would
drain across the asphalt to the south, and eventually into the unpaved areas south of the Air
Center to either the outfall or stormwater drain.

3.2. AOI 2—-—POSSIBLE FTA

AOI 2 includes the area adjacent to the helipad area where a fire extinguisher possibly containing
AFFF may have once been discharged into the adjacent unpaved soil. The area outside of the
helipad area was identified as a possible FTA and identified as a separate AOI since the area
crosses the property boundary. Historical research and interviews indicated fire training did not
regularly occur on the Facility. Personnel had anecdotal knowledge that a fire extinguisher may
have been discharged by a guardsman on the unpaved sandy area at the southwest edge of the
asphalt helipads as part of an unofficial training exercise. A specific timeframe for this event was
not given; however, personnel indicated it would have been prior to 2003. Because details are
not specifically recalled, this training event is considered a potential AFFF release. If a release
were to have occurred, the release would flow in the unpaved areas south of the Air Center to
either the outfall or stormwater drain.

3.3. ADJACENT SOURCES

Hangars | and 2 are adjoined to the east by a separate series of hangars located within the
Cheyenne Air Center. One potential off-facility source of PFAS is adjacent to the Facility and is
not under the control of the NVARNG. A description of the off-Facility source is presented
below and shown on Figure 3-1.

EA Engineering, Science, and Technology, Inc., PBC 3-1


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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

oF

>

%
pg/kg

AASF
AECOM
AFFF
amsl
ANG
AOI
ARNG

bgs

CERCLA
Coc
CSM

DA
DoD
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HQ

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LIST OF ACRONYMS AND ABBREVIATIONS

Degrees Fahrenheit

greater than

Percent

Microgram(s) per kilogram

Army Aviation Support Facility
AECOM Technical Services, Inc.
Aqueous Film Forming Foam
Above mean sea level

Air National Guard

Area of Interest

Army National Guard

Below ground surface

Comprehensive Environmental Response, Compensation, and Liability Act
Chain-of-custody
Conceptual site model

Department of the Army
Department of Defense
Data quality indicator
Data quality objective
data usability assessment

EA Engineering, Science, and Technology, Inc., PBC
Extraction internal standards

Environmental Laboratory Accreditation Program
Engineer Manual

Equipment Blank

Federal Aviation Administration
Field blank

Federal Express

Foot (feet)

foot per foot

fire training area

geographic information system
Ground penetrating radar

High-density polyethylene
Hexafluoropropylene oxide dimer acid
Hazard Quotient

hollow-stem auger

EA Engineering, Science, and Technology, Inc., PBC vi


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Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

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EA Engineering, Science, and Technology, Inc., PBC 8-4


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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

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 SIACTIVITIES

The SI field activities at the Facility were conducted from 30 January to 13 February 2023. The
SI field activities included soil and groundwater sampling. Field activities were conducted in
accordance with the UFP-QAPP Addendum (EA/Wood, 2022a), except as previously noted in
Section 5.8.

To fulfill the project DQOs set forth in the approved SI UFP-QAPP Addendum (Wood, 2022a),
samples were collected and analyzed for a subset of PFAS by LC/MS/MS compliant with QSM
5.3 Table B-15 as follows.

e 15 soil grab samples from five boring locations;
e Six grab groundwater samples from six temporary well locations; and,
e Nine QA/QC samples.

An SI is conducted when the PA determines an AOI exists based on probable use, storage, and/or
disposal of PFAS-containing materials. The SI includes multi-media sampling at AOIs to
determine whether or not a release has occurred. The SI may conclude further investigation is
warranted, a removal action is required to address immediate threats, or no further action is
required. Additionally, the CSMs were refined to assess whether a potentially complete pathway
exists between the source and potential receptors for potential exposure at the AOIs, which are
described in Section 7.0.

8.2, OUTCOME

The SI results indicate PFBS, PFHxS, PFOS, and PFOA are present in groundwater upgradient
of AOI 1 and AOI 2 at levels similar to those detected at AOI 1 and AOI 2. PFOS was detected
at a concentration equal to the SL of 4.0 ng/L near the upgradient boundary of AOI 1. The SL for
PFOS in groundwater was exceeded at AOI 2, with a maximum concentration of 4.4 J ng/L. The
surface soil, subsurface soil, and groundwater results suggest the contamination present in
groundwater is not likely associated with NVARNG and DoD activities. Therefore, no further
action by ARNG is warranted at AOI 1 and AOI 2 (see Table 8-1). (see Table 8-1).

Sample analytical concentrations collected during the SI were compared against the project SLs
in soil and groundwater, as described in Table 6-1. A summary of the results of the SI data
relative to SLs is as follows:

At AOI 1:

EA Engineering, Science, and Technology, Inc., PBC 8-1


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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

decontamination of drilling equipment during the SI are provided in Appendix F. A discussion
of the results is presented in the Data Usability Assessment (Appendix A).

Materials that were used within the sampling zone were confirmed as acceptable for use in the
PFAS sampling environment. The checklist of acceptable materials for use in the PFAS sampling
environment was provided in the Standard Operating Procedures appendix to the Programmatic
UFP-QAPP (PQAPP) (EA/Wood, 2022a).

5.2, SOIL BORINGS AND SOIL SAMPLING

Soil samples were collected via rotosonic drilling methods in accordance with Standard
Operating Procedure 025 and 047 Rotosonic Drilling and Sampling (EA/Wood, 2021a). A 600-T
rotosonic drilling rig was used to collect continuous soil cores to the target depth. A hand auger
was used to collect soil from the top 5 ft of the boring in compliance with utility clearance
procedures. The soil boring locations are shown on Figure 5-1, and boring sample depths are
provided in Table 5-1. Several boring locations were adjusted within a 50-feet offset for reasons
including drill rig access, utility avoidance and bias toward sampling within observed drainage
features.

Three discrete soil samples were collected for chemical analysis from each soil boring: one
sample at the surface (0 to 2 ft bgs) and two subsurface soil samples. One subsurface soil sample
was collected approximately 1 ft above the groundwater table, and one was collected at the mid-
point between the surface and the groundwater table (not to exceed 15 ft bgs). Groundwater was
encountered at depths ranging from 35 to 37 ft bgs during drilling. Total boring completion
depths, to accommodate temporary well installation, ranged from 42 to 45 ft bgs.

During the drilling, the soil cores were continuously logged for lithological descriptions by a
field geologist using the Unified Soil Classification System. Soils were predominately described
as sandy clay and clayey sand with interbedded layers of gravels, medium plastic fines (clay),
and less plastic fines (silt). Caliche also known as calcium carbonate deposits were also observed
in the borings at thicknesses ranging from a few inches to approximately 5 ft. These observations
are consistent with the understood depositional environment of the region. A photoionization
detector (PID) was used to screen the breathing zone during boring activities as a part of personal
safety requirements. Observations and measurements were recorded on sampling forms
(Appendix B2) and in a non-treated field logbook. Depth interval, recovery thickness, PID
concentrations, moisture, relative density, Munsell color, and Unified Soil Classification System
texture were recorded. The boring logs are provided in Appendix E.

Each sample was collected into a laboratory-supplied PFAS-free high-density polyethylene
(HDPE) bottle and labeled using a PFAS-free marker or pen. Samples were packaged on ice and
transported via FedEx under standard chain of custody (COC) procedures to the laboratory and
analyzed for PFAS (LC/MS/MS compliant with QSM Version 5.3 Table B-15), total organic
carbon (TOC) (EPA Method 9060A), pH (EPA Method 9045D), and grain size (ASTM Method
D-422) in accordance with the UFP-QAPP Addendum (EA/Wood 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

EA Engineering, Science, and Technology, Inc., PBC 5-3


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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

parameters as the accompanying samples. In instances when non-dedicated sampling equipment
was used, such as a hand auger for the shallow soil samples, an EB was collected and analyzed
for the same parameters as the soil samples. A temperature blank was placed in each cooler for
use in confirming that samples were preserved at or below 6 degrees Celsius (°C) during
shipment.

Rotosonic borings were converted to temporary wells, which were subsequently abandoned after
sampling and surveying in accordance with the UFP-QAPP Addendum (EA/Wood, 2022a).
After removal of the casings, boreholes were abandoned using Portland cement and surfaces
patched with similar material.

5.3 TEMPORARY WELL INSTALLATION AND GROUNDWATER GRAB
SAMPLING

Temporary wells were installed using a 600-T Sonic continuous core sampling system. Once the
borehole was advanced to the desired depth, a temporary well was constructed of a 10-ft section
of 2-inch Schedule 40 poly-vinyl chloride (PVC) screen with sufficient casing to reach the
ground surface. New PVC pipe and screen were used at each location to avoid cross
contamination between locations. The screen intervals for the temporary wells are provided in
Table 5-2.

Groundwater samples were collected after a period of time following well installation to allow
groundwater to infiltrate and recharge the temporary well screen intervals. After the recharge
period, groundwater samples were collected using a low flow submersible pump with PFAS-free
HDPE tubing. The temporary wells were purged at a rate determined in the field to reduce
turbidity and draw down prior to sampling. Water quality parameters (e.g., temperature, specific
conductance, pH, dissolved oxygen, and oxidation-reduction potential) were measured using a
water quality meter and recorded on the field sampling form (Appendix B2) before each grab
sample was collected in a separate container.

Each sample was collected in laboratory-supplied PFAS-free HDPE bottles and labeled using a
PFAS-free marker or pen. Samples were packaged on ice and transported via FedEx under
standard COC procedures to the laboratory and analyzed for PFAS by LC/MS/MS compliant
with QSM Version 5.3 Table B-15 in accordance with the UFP-QAPP Addendum (EA/Wood,
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. Three FBs was collected in accordance with the UFP-
QAPP Addendum (EA/Wood, 2022a). In instances when non-dedicated sampling equipment was
used, such as a stainless-steel bow! or sampling pump, one EB was collected per sampling
equipment and analyzed for the same parameters as the groundwater samples, but EBs were not
collected daily as noted in Section 5.8. A temperature blank was placed in each cooler for use in
confirming that samples were preserved at or below 6°C during shipment.

Following well surveying (described below in Section 5.5), temporary wells were abandoned in
accordance with the SI UFP-QAPP Addendum (EA/Wood, 2022a) by removing the PVC and

EA Engineering, Science, and Technology, Inc., PBC 5-4


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Site Inspection Report
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EA Engineering, Science, and Technology, Inc., PBC 2-14


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Site Inspection Report

Cheyenne Army Aviation Support Facility, Nevada Version: FINAL
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Cheyenne Army Aviation Support Facility NY

Las Vegas, Nevada
Figure 5-1
Site Inspection Sample Locations

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Data Sources: ESRI 2020, AECOM 2019

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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

Table 5-2 Soil Boring Depths and Temporary Well Screen Intervals
Cheyenne Army Aviation Support Facility, Las Vegas, Nevada

Site Inspection Report

Temporary Well
Area of Interest Boring Location Sol pe i Gul Screen Interval
= (ft bgs)

1 AOI01-01 42.9 32.90 - 42.90
AOI01-02 42.38 32.38 - 42.38
2 AOI02-01 44.34 34.34 - 44.34
AOI02-02 42.23 32.23 - 43.23
Boundary Wells AASF-01 45.32 35.32 - 45.32
AASF-02 43.09 33.09 - 43.09

Notes:

' Temporary well screen set above total depth to capture groundwater interface
AASF = Army Aviation Support Facility

ams! = Above mean sea level

bgs = below ground surface

btos elow top of casing

NA = not applicable

NAVD88 = North American Vertical Datum 1988

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2. FACILITY BACKGROUND
2.1 FACILITY LOCATION AND DESCRIPTION

Cheyenne AASF is located in the city of North Las Vegas, about 5 miles northwest of downtown
Las Vegas, Nevada (Figure 2-1). The AASF leases a small portion (approximately 0.4 acre) of
hangar space, Hangar 1 and 2, from the Cheyenne Air Center (approximately 9.5 acres), that is
located on the north edge of the North Las Vegas Airport in North Las Vegas, Nevada. The
North Las Vegas Airport opened in 1941 encompassing approximately 920 acres. The Cheyenne
Air Center is a privately-owned company servicing private airplanes, as well as some aviation
tour companies. NVARNG leases hangar space for the AASF, Hangar | and Hangar 2, and
office space in a portion of a large building shared with other tenants. The NVARNG lease was
renewed in September 2023. NVARNG’s lease agreement does not include the helipad and the
paved areas within the Cheyenne Air Center. NVARNG’s access to these areas is informally
managed directly with the property owner. Hangar 1 is leased to the Rochelle Aizenberg
Revocable Trust and then, starting in 2018, subleased to the NVARNG. Hangar 2 is leased to
NVARNG by a private owner per a 2018 agreement (AECOM, 2020). A possible fire training
area (FTA) is located to the southwest of the Cheyenne Air Center property, and within the
North Las Vegas Airport property boundary (EA/Wood, 2022a). The approximate geographic
coordinates for the center of the FTA are 36°21°64.89”N; 115°20°22.19"W.

2.2. FACILITY ENVIRONMENTAL SETTING

The AASF is located in the southern tip of Nevada at an elevation of approximately 2,205 feet
(ft) above mean sea level. The Facility is covered by the U.S. Geological Survey (USGS) Las
Vegas Northwest 7.5-minute quadrangle topographic map. The Facility is developed with two
hangars, concrete, and asphalt features. AOI 2 is located within the North Las Vegas Airport
property boundary on native soil with asphalt millings. The Cheyenne Air Center and the North
Las Vegas Airport have controlled access.

The Facility and city of North Las Vegas are located within the Las Vegas Valley, which is a
structural hydrologic basin made of alluvial-fan deposits and fault bounded. The Las Vegas
Valley consists of about 1,600 square miles located mostly in the Mojave Desert except for the
foothills in the northwest portion of the valley.

2.2.1 Geology

Cheyenne AASF is located in the Basin and Range geomorphic province, where east-west
extensional tectonic movement (spreading) has created a large number of north-south oriented
block faulted mountain ranges. The area is situated in the southern part of the Las Vegas Valley,
which is northwest trending, generally following the right lateral strike-slip character of the Las
Vegas shear zone. This fault cuts the thrust system at right angles, offsetting the southern tier of
mountains to the west. The Las Vegas Valley itself has been formed by the pulling apart of block
faulted ranges by drag effects of displacements along the Las Vegas shear zone.

The Las Vegas Valley is a fault-bounded structural and hydrologic basin containing hundreds of
feet of late Tertiary and Quaternary lacustrine, paludal, and alluvial deposits. These sediments

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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

Groundwater supplies in the Las Vegas Valley come from three major primary aquifer zones
generally located from 300 to 1,500 ft below land surface. Thick layers of clay and fine-grained
sediment separate these primary aquifers from the shallow aquifers, which lie within 50 ft bgs.
All groundwater in the Las Vegas Valley comes from the snowmelt and rainfall from mountain
ranges surrounding the valley. Most of the wells in the Las Vegas area draw water from the
primary principal aquifer system, which is several hundred feet thick. This aquifer system is
confined by an aquitard, which is about 200 ft thick.

A 4-mile radius surrounding the facility was searched for existing wells using an EDRTM report
and additional online resources, such as state and local geographic information system (GIS)
databases. No on-site water wells or springs exist on the Facility (Figure 2-3). Domestic wells
surround the facility along with monitoring wells upgradient and downgradient of the facility.
There are also commercial and irrigation wells located upgradient of the Facility. Public supply
wells are located upgradient and downgradient of the Facility.

The Facility’s potable water is supplied by the municipality of North Las Vegas receiving water
primarily from Lake Mead and 10% from local groundwater. PFAS analysis was not included in
the City of North Las Vegas 2022 Water Quality Report. Potable water at the Facility was
sampled prior to the field mobilization, and PFAS compounds were below their applicable
screening levels.

2.2.3, Hydrology

The topography in the area of the AASF is relatively flat, and surface water generally drains
towards the southeast. No lakes, ponds, streams, retentions basins, or areas of standing water are
located on or immediately adjacent to the Facility.

The eastern edge of the Las Vegas Valley is located approximately 5 miles west of Lake Mead,
which serves as an impoundment on the Colorado River. The Las Vegas Wash is fed by
tributaries that channel most shallow groundwater and all surface water in the western Las Vegas
Valley (i.e., tributaries of the Colorado River) into the Las Vegas Wash, which flows into Lake
Mead via the Las Vegas Bay. According to LVVWD, less than 2% of Lake Mead’s water comes
from the Las Vegas Wash, and the remaining water is sourced from snowmelt into the Colorado
River. Southern Nevada gets nearly 90% of its water from the Colorado River, which begins as
snowmelt in the Rocky Mountains.

At the Cheyenne Air Center, stormwater is channeled from the exterior pavement surfaces into
drainage features, including gutters within the paved area, open drainage channels, outflow
drains, and drop inlets. These features convey stormwater towards the south and southeast,
discharging into an open drainage channel, located on the North Las Vegas Airport
approximately 0.2 miles to the south of the Facility. Surface water in the open drainage channel
flows to the east for approximately one-half mile then to the south. The surface water eventually
discharges to the Carey Avenue/Lake Mead detention pond, located approximately 1.5 miles to
the southeast of the Facility, which discharges into the City of North Las Vegas storm water
drainage system. The City of North Las Vegas storm water drainage system conveys stormwater
runoff into the Las Vegas Wash and its tributaries. Water features near the Facility are shown in
Figure 2-5.

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TABLE OF CONTENTS

Page

DIS TOR APPENDICES sissiesstssaiasccisssssizcasusstsssisassvsdeasaasceadoostosobosvesssstesagcoscapssbasssaasasapenssaasascesegsate iii
TIES TU QE BIG URES crssesscucncaceausaveerarariesticapes Gees cies Seisiek BUA 6h ke alee SORBET OARS Sf STTCTRT TS TOTTI EET iv
LISTOP TABLES: castiarsdaasauihuthitininaioncnamommaadianmaninndionihered! v
LIST OF ACRONYMS AND ABBREVIATIONS ............:cssssssssssssssssesssscessscsvssssessacsesscassnsesares vi
BXECUDIVE-SUMMARY éeicccsaseieacedeizcsutsesiesssestcscnieasclecesstesosetuvsesteasteecussetyasisesesssieistsonsdeisocezaises 1
1. INTRODUCTION 525 csdeccatsesticensuossliouduossascbiecabehvssncnapesdieedtenetisuatsvisbeeetanstinictted 1-1

1.1 Project Authorization...
1.2 Site Inspection Purpose.

Ze RACILTTY: BACKGROUND i sisdsssaseweats cassesncsahssapteatetecatessetneaes tobsssasavastensintease 2-1

| Facility Location And Description.
2.2 Facility Environmental Setting ...

2.2.1 Geology
2.2.2 Hydrogeology
2.2.3 Hydrology
2.2.4 Climate...
2.2.5 Current and Future Land Use.
2.2.6 Sensitive Habitat and Threatene

23 History Of PRAS Wee: scstetesscatscesssrihosecentpcecgeeiteesinsckesckseetussoevisahaa nthe fader 2-5
3. SUMMARY OF AREAS OF INTEREST ...0.:...:-.sscscsssecosseptsesssseesenseeseeebencsttoenses 3-1
3.1 AOI | — Hangars and Helipad Area 3-1

3.2 AOI2~—Possible FTA.
3.3 Adjacent Sources

3.3.1 North Las Vegas Airport. scicisseseiesesessesesessacetetessesseseieseacetesezends 3-2
4. PROJECT DATA QUALITY OBJECTIVES .....:ssssssssssssoseosossssosesssvssessssosessenose 4-1

Al Problem Statement
4.2 Information Inputs .
43 Study Boundaries
44 — Analytical Approach.
4.5 Data Usability Assessmen:

5. SITE INSPECTION: ACTIVITIES iissstissssssssassssssscsisasscssessesssassassdsssieastssssisanaaea 5-1

5.1 Pré-Investigntiom A chvities.i5.i..c.dcisidsdsccivasnéctssesteisSonice ivesunsesedstcateceinassces 5-2

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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 of these activities are presented below.

5.1.1 Technical Project Planning

The USACE TPP Process, Engineers Manual (EM) 200-1-2 (Department of the Army, 2016a)
defines four phases to project planning: (1) defining the project phase; (2) determining data
needs; (3) developing data collection strategies; and (4) finalizing the data collection plan. The
process encourages stakeholder involvement in the SI, beginning with defining overall project
objectives, including DQOs, and formulating a sampling approach to address the AOIs identified
in the PA.

A combined TPP Meeting 1 and 2 was held on 21 October 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 included ARNG, NVARNG, USACE, Nevada Division of
Environmental Protection (NDEP), and representatives familiar with the Facility, the regulations,
and the community. Stakeholders were provided the opportunity to make comments on the
technical sampling approach and methods at the combined TPP Meeting | and 2. The outcome of
the combined TPP Meeting | and 2 was memorialized in the UFP-QAPP Addendum (EA/Wood,
2022a).

A TPP Meeting 3 was held on 05 December 2023 after the field event to discuss the results of
the SI. Meeting minutes for TPP 3 are included in Appendix D of this report. The TPP meeting
provided an opportunity to discuss results and findings, and future actions, where warranted.

5.1.2 Utility Clearance

WSP USA Environment & Infrastructure Inc. (WSP), previously doing business as Wood
Environment & Infrastructure Solutions, Inc., contacted the Utility Notification Center
(Underground Service Alert) to notify them of intrusive work at the Facility. WSP contracted
GPRS LLC., a private utility location service, to perform utility clearance at the Facility. Utility
clearance was performed at each of the proposed boring locations on 17 January 2023 with input
from the WSP field team. General locating services and ground-penetrating radar (GPR) were
used to complete the clearance. Additionally, the first 5 feet of each boring were pre-cleared by
WSP’s drilling subcontractor, Cascade Drilling, LP (Cascade), using a hand auger to verify
utility clearance in shallow subsurface where utilities would typically be encountered.

5.1.3 Source Water and PFAS Sampling Equipment Acceptability

The potable water source used for decontamination of drilling equipment was confirmed to meet
acceptability criteria, as defined in the UFP-QAPP Addendum, prior to the start of field
activities. A sample from a potable water source at Cheyenne AASF, was collected on 29 August
2022, prior to mobilization, and analyzed for PFAS by LC/MS/MS compliant with QSM 5.3
Table B-15 (DoD, 2020). The results of the sample of the potable water source used for

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results (2 to 15 ft bgs). The SLs are not applied to deep subsurface soil results (greater than [>]
15 ft bgs) because 15 ft is the anticipated limit of construction activities.

6.2 SOIL PHYSICOCHEMICAL ANALYSES

To provide basic soil parameter information, one soil sample per AOI was analyzed for TOC,
pH, and grain size, which are important for evaluating transport through the soil medium.
Appendix E 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 PFAS partitioning mechanisms include hydrophobic and
lipophobic effects, electrostatic interactions, and interfacial behaviors. At relevant environmental
pH values, certain PFAS are present as organic anions, and are therefore relatively mobile in
groundwater (Xiao et al., 2015), but tend to associate with the organic carbon fraction that may
be present in soil or sediment (Higgins and Luthy, 2006; Guelfo and Higgins, 2013). When
sufficient organic carbon is present, organic carbon normalized distribution coefficients (Koc
values) can help in evaluating transport potential, though other geochemical factors (for example,
pH and presence of polyvalent cations) may also affect PFAS sorption to solid phases (ITRC,
2018).

63 AOI1

This section presents the analytical results for soil and groundwater in comparison to SLs for
AOI 1: Hangars and Helipad Area. The soil and groundwater results are summarized in Table 6-
2 through Table 6-5. Soil and groundwater results are presented on Figures 6-1 through Figure
6-7.

6.3.1 AOI 1 Soil Analytical Results

Soil samples were collected from two boring locations associated with AOI 1 during the SI.
Figure 6-1 through Figure 6-5 present the ranges of detections in soil. Tables 6-2 through Table
6-4 summarize the soil results.

Surface soil (0 to 2 ft bgs) was sampled from boring locations AOI01-01 and AOI01-02. Soil
was also sampled from shallow subsurface soil (13 to 15 ft bgs) and deep subsurface soil
intervals (34 to 35 ft bgs) from boring locations AOI01-01 and AOI01-02. No relevant
compounds (PFBS, PFHxS, PFNA, PFOS, and PFOA) were detected in the soil samples
(surface, shallow subsurface, and deep subsurface).

6.3.2, AOI 1 Groundwater Analytical Results

Groundwater samples were collected from three temporary wells associated with AOI 1 during
the SI. Figure 6-6 and Figure 6-7 presents the ranges of detections in groundwater. Table 6-5
summarizes the groundwater results.

Groundwater was sampled from temporary monitoring well locations AOI01-01, AOI01-02, and
AASF-02, located upgradient of AOI 1. PFOS was detected in groundwater at a concentration

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Table 5-1 Site Inspection Samples by Medium
Cheyenne Army Aviation Support Facility, Las Vegas, Nevada

Site Inspection Report

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Sample Identification Collection i 3 2ia s\/= pat Comments
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Soil Samples
AOI01-01-SB-0.5-2.5 2/11/2023 x
AOI01-01-SB-13-15 2/11/2023 xX Parent sample of FD-03
CHEYENNE-FD-03 2/11/2023 x
AOI01-01-SB-34-35 2/11/2023 x xX x xX
AOI01-02-SB-0.5-2.5 2/11/2023 xX Parent sample of FD-02
CHEYENNE-FD-02 2/11/2023 x
AOI01-02-SB-13-15 2/11/2023 Xx
AOI01-02-SB-34-35 2/11/2023 x MS/MSD
AO102-01-SB-0,5-2.5 2/9/2023 Xx
AO102-01-SB-13-15 2/9/2023 x
AO102-01-SB-34-35 2/9/2023 Xx
AOI102-02-SB-0,5-2.5 2/10/2023 x x x Xx
AO102-02-SB-13-15 2/10/2023 X
AOI102-02-SB-34-35 2/10/2023 Xx
AASF-01-SB-0.5-2.5 2/9/2023 xX
AASF-01-SB-13-15 2/9/2023 x
AASF-01-SB-34-35 2/9/2023 xX
Groundwater Samples
AOI01-01-GW 2/11/2023 X
AOI01-02-GW. 2/10/2023 x
AOI02-01-GW 2/10/2023 x Parent sample of FD-01
CHEYENNE-FD-01 2/10/2023 x
AOI02-02-GW 2/10/2023 x
AASF-01-GW. 2/9/2023 Xx
AASF-02-GW 2/11/2023 xX MS/MSD
Blank Samples
CHEYENNE-EB-01 2/9/2023 x Equipment Blank from the Steel]
Bowl
CHEYENNE-EB-02 2/10/2023 x Equipment Blank from the
Hand Auger and Steel Mixing
Bowl
CHEYENNE-EB-03 2/11/2023 x Equipment Blank from the
Groundwater Sampling Pump
CHEYENNE-FB-01 2/9/2023 X
CHEYENNE-FB-02 2/10/2023 xX
CHEYENNE-FB-03 2/11/2023 xX
Notes:

AASF = Army Aviation Support Facility

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Site Inspection Report
Cheyenne Army Aviation Support Facility

Las Vegas, Nevada
Figure 2-5
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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

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) at ARNG facilities nationwide based on the current
or potential historical use of per- and polyfluoroalky! substances (PFAS) with a focus on the six
compounds presented in the memorandum regarding Investigating Per- and Polyfluoroalkyl
Substances within the Department of Defense Cleanup Program (Assistant Secretary of Defense,
2022) from the Office of the Secretary of Defense (OSD) dated 6 July 2022. The six compounds
listed in the OSD memorandum are referred to as “relevant compounds” throughout this
document and include perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA),
perfluorobutanesulfonic acid (PFBS), perfluorononanoic acid (PFNA), perfluorohexanesulfonic
acid (PFHxS), and hexafluoropropylene oxide dimer acid (HFPO-DA)'. The ARNG performed
this SI at the Cheyenne Army Aviation Support Facility (AASF) in Las Vegas, Nevada (NV).
The Cheyenne AASF is also referred to as the “Facility” throughout this report

The SI project elements were performed in accordance with the Comprehensive
Environmental Response, Compensation, and Liability Act (CERCLA) (U.S. Environmental
Protection Agency [EPA] 1980), as amended, the National Oil and Hazardous Substances
Pollution Contingency Plan (40 Code of Federal Regulations Part 300; EPA 1994), and in
compliance with U.S. Department of Army (DA) requirements and guidance for field
investigations.

1.2 SITE INSPECTION PURPOSE

A PA was performed at the Cheyenne AASF (AECOM Technical Services, Inc. [AECOM]
2020) that identified one Area of Interest (AOI), subsequently divided into two 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
AOlIs 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.

' 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 S]. 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.

EA Engineering, Science, and Technology, Inc., PBC 1-1


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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

equal to the SL at one location and below the SL at the other two locations. PFBS, PFHxS, and
PFOA were detected at concentrations below their respective SLs at AOI01-01, AOI01-02, and
AASF-02.

PFOS was detected at the screening level of 4.0 ng/L at AASF-02. PFOS was detected below the
SL at AOIO1-01 and AOIO1-02 at concentrations of 3.7 ng/L and 3.9 ng/L, respectively. All
three locations (AOI01-01, AOI01-02, and AASF-02) had detections of PFBS below the SL at
concentrations ranging from 1.2 J to 3.0 ng/L. All three locations (AOI01-01, AOI01-02, and
AASF-02) had detections of PFHxS below the SL at concentrations ranging from 4.6 to 5.3 ng/L.
All three locations (AOI01-01, AOI01-02, and AASF-02) had detections of PFOA below the SL
at concentrations ranging from 2.8 to 3.6 ng/L. PFNA was not detected in the groundwater
samples.

6.3.3, AOI 1 Conclusions

Based on the results of the SI, no relevant compounds (PFBS, PFHxS, PFNA, PFOS, and PFOA)
were detected in soil samples (surface, shallow subsurface, and deep subsurface). PFOS was
detected in upgradient temporary well AASF-02 at a concentration equal to the screening level of
4.0 ng/L, indicating a possible upgradient source. PFOS was detected in groundwater from the
other two AOI | temporary wells below the SL. PFBSs, PFHxS, and PFOA were detected in
groundwater at concentrations at or below their respective SLs. There were no exceedances of
the SLs in soil or groundwater, and no further evaluation at AOI 1 is warranted.

6.4 AOI2

This section presents the analytical results for soil and groundwater in comparison to SLs for
AOI 2: Possible FTA. The soil and groundwater results are summarized in Table 6-2 through
Table 6-5. Soil and groundwater results are presented on Figures 6-1 through Figure 6-7

6.4.1 AOI 2 Soil Analytical Results

Soil samples were collected from three boring locations associated with AOI 2 during the SI.
Figure 6-1 through Figure 6-5 present the ranges of detections in soil. Tables 6-2 through Table
6-4 summarize the soil results.

Surface soil (0 to 2 ft bgs) was sampled from boring locations AOI02-01, AOI02-02, and AASF-
01. Soil was also sampled from shallow subsurface soil (13 to 15 ft bgs) and deep subsurface soil
intervals (34 to 35 ft bgs) from boring locations AOI02-01, AOI02-02, and AASF-01. PFNA,
PFOS, and PFOA were detected in surface soil at concentrations below their respective SLs at
AOI02-01, PFOA was also detected in surface soil at a concentration below the SL at AASF-01.

One of the three locations (AOI02-01) had a detection of PFNA in surface soil at a concentration
of 0.29 J g/kg. One of the three locations (AOI02-01) had detections of PFOS at a
concentration of 0.73 g/kg. Two of the three locations (AOI02-01 and AASF-01) had detections
of PFOA at concentrations of 0.45 J j1g/kg and 0.27 J pg/kg, respectively. PFBS and PFHxS
were not detected in the surface soil samples.

EA Engineering, Science, and Technology, Inc., PBC 6-3


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Site Inspection Report
Cheyenne Army Aviation Support Facility, Nevada Version: FINAL

consist of poorly compressible, coarse-grained alluvial-fan deposits around the valley margins
and of highly compressible, fine-grained sediment in the middle of the valley. The Las Vegas
Valley drains into Lake Mead via the Las Vegas Wash and is part of the overall Colorado River
drainage system. A low divide north of Las Vegas separates the main part of the valley from the
interior draining basins to the north. The valley lies between the Spring Mountains to the west,
which reach an altitude of 12,000 ft, and the much lower Frenchman (4,000 ft) and Sheep
Mountains and Las Vegas Ranges (10,000 ft) to the east.

The alluvium consists of unconsolidated gravel, sand, silt, and clay deposits. During the SI,
unconsolidated sediments at the Facility were dominated by sandy clay and clayey sand
interbedded with layers of gravels and medium plastic fines (silt/clay). The borings were
completed at depths between 42 to 45 ft below ground surface (bgs).

A sample for grain size analysis was collected at one location per AOI; AOI01-01 and AOI02-01
and analyzed via American Society for Testing and Materials (ASTM) Method D-422. The
results for AOI 1 indicate that the soil of the AOI is comprised primarily of gravel (37.5 percent
[%]) and sand (30.9%), with clay (17.6%) and silt (14%). The results for AOI 2 indicate that the
soil of the AOI is comprised primarily of silt (48.1%) and clay (35.7%) with sand (13.4%) and
gravel (2.8%). These results and Facility observations are consistent with the reported
depositional environment of the region primarily consisting of coarse-grained deposits (gravel
and sand) and fine-grained deposits (silt and clay).

2.2.2. Hydrogeology

The Las Vegas Valley is underlain by coalescing alluvial fans mostly originating on the front of
the Spring Mountains and Sheep Range. These fans contain lenticular and irregularly distributed
aquifers of permeable sand and gravel, separated by aquitards of silt and clay that are nearly
impermeable, creating a large artesian groundwater system.

The Facility is underlain by silt with discrete layers of sand, clay, or gravel. Based on the soil
survey published by the U.S. Department of Agriculture (USDA) Soil Conservation Service, the
Facility encompasses one mapped soil unit, Skyhaven, which is a very fine sandy loam. The
Facility’s hydrologic soil group classification is “Class C, slow infiltration rates, soils with layers
impeding downward movement of water or soils with moderately fine or fine textures.” The soil
drainage classification is “well drained.”

According to the Nevada Division of Water Resources online database, groundwater in the
region flows southeast. The depth to static groundwater measured in February 2023 during the SI
ranged from approximately 29.90 to 34.45 ft bgs. Based on groundwater elevations calculated
using depth to groundwater measurements and survey data collected during the SI, groundwater
flows to the southeast with an approximate gradient of 0.0082 foot per foot (ft/ft). Groundwater
elevation contours from the SI are presented on Figure 2-4.

Southern Nevada gets roughly 10% of its water supply from groundwater. The Las Vegas Valley

Water District (LVVWD) pumps groundwater from wells to meet peak summer demand. During

the hot summer months from June through September, groundwater can account for up to 25% of
the LVVWD’s daily water supplies.

EA Engineering, Science, and Technology, Inc., PBC 2-2