FINAL

Preliminary Assessment Report

Rapid City Army Aviation Support Facility, 

South Dakota

Perfluorooctane-Sulfonic Acid (PFOS) and Perfluorooctanoic Acid (PFOA) 

Impacted Sites

ARNG Installations, Nationwide

August 2020

Prepared for:

Army National Guard Bureau

111 S. George Mason Drive

Arlington, VA 22204

UNCLASSIFIED
PFAS Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

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Table of Contents

Executive Summary ....................................................................................................................1

1. Introduction........................................................................................................................4

Authority and Purpose ..............................................................................................4

Preliminary Assessment Methods .............................................................................4

Report Organization..................................................................................................5

Facility Location and Description...............................................................................5

Facility Environmental Setting...................................................................................5

1.5.1 Geology .........................................................................................................6

1.5.2 Hydrogeology................................................................................................. 6

1.5.3 Hydrology.......................................................................................................7

1.5.4 Climate...........................................................................................................7

1.5.5 Current and Future Land Use.........................................................................7

2. Fire Training Areas...........................................................................................................11

3. Non-Fire Training Areas ...................................................................................................12

Main Hangar...........................................................................................................12

Old Hangar – Bay 1 ................................................................................................13

Cold Storage Hangar ..............................................................................................13

4. Emergency Response Areas............................................................................................15

5. Adjacent Sources.............................................................................................................16

Rapid City Fire Department.....................................................................................16

Ellsworth AFB .........................................................................................................16

Landfills ..................................................................................................................16

6. Preliminary Conceptual Site Model ..................................................................................18

AOI 1 Overflow Area ...............................................................................................18

7. Conclusions .....................................................................................................................21

Findings ..................................................................................................................21

Uncertainties...........................................................................................................21

Potential Future Actions ..........................................................................................22

8. References ......................................................................................................................24
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Tables

Table ES-1: AOIs at Rapid City Army Aviation Support Facility

Table 7-1: AOIs at Rapid City Army Aviation Support Facility

Table 7-2: No Suspected Release Areas

Table 7-3: Uncertainties

Table 7-4: PA Findings Summary

Figures

Figure ES-1 Summary of Findings

Figure ES-2 Preliminary Conceptual Site Model, Rapid City AASF, South Dakota

Figure 1-1 Facility Location

Figure 1-2 Groundwater Features

Figure 1-3 Surface Water Features

Figure 3-1 Non-Fire Training Areas

Figure 5-1 Adjacent Sources

Figure 6-1 Area of Interest

Figure 6-2 Preliminary Conceptual Site Model, AOI 1 Overflow Area

Figure 7-1 Summary of Findings

Appendices

Appendix A Data Resources

Appendix B Preliminary Assessment Documentation

 B.1 Interview Records

 B.2 Visual Site Inspection Checklists

 B.3 Conceptual Site Model Information

Appendix C Photographic Log
PFAS Preliminary Assessment Report

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Acronyms and Abbreviations

AASF Army Aviation Support Facility

AECOM AECOM Technical Services, Inc.

AFB Air Force Base

AFFF aqueous film forming foam

AOI Area of Interest

ARNG Army National Guard

CERCLA Comprehensive Environmental Response, Compensation, and Liability 

Act

EDRTM Environmental Data Resources, Inc.TM 

DLA Defense Logistics Agency

°F degrees Fahrenheit

FTA fire training area

PA Preliminary Assessment

PFAS per- and poly-fluoroalkyl substances

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

SDARNG South Dakota Army National Guard

SI Site Inspection

US United States

USACE United States Army Corps of Engineers

USEPA United States Environmental Protection Agency

UST underground storage tank
PFAS Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

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Executive Summary

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

Inspections (SIs) for Perfluorooctanesulfonic acid (PFOS) and Perfluorooctanoic acid (PFOA) 

Impacted Sites at ARNG Facilities Nationwide. A PA for per- and polyfluoroalkyl substances 

(PFAS)-containing materials was completed for South Dakota Army Aviation Support Facility

(AASF; also referred to as the “facility”) in Rapid City, South Dakota, to assess potential PFAS 

release areas and exposure pathways to receptors. The AASF is constructed on approximately 

33.7 acres of land owned by the City of Rapid City and has been leased to the State of South 

Dakota Department of Military and Veterans Affairs since 1957 for a term of 99 years. 

The performance of this PA included the following tasks: 

• Reviewed available administrative record documents and Environmental Data Resources, 

Inc. (EDR)TM report packages to obtain information relevant to potential PFAS releases, such 

as: drinking water well locations, historical aerial photographs, Sanborn maps, and 

environmental compliance actions in the area surrounding the facility;

• Conducted a site visit 10 September 2019 and completed visual site inspections at locations 

where PFAS-containing materials were suspected of being stored, used, or disposed;

• Interviewed current and retired SDARNG personnel, SDARNG environmental managers, and

operations staff; 

• Completed visual site inspections at known or suspected potential PFAS release locations

and documented with photographs; 

One Area of Interest (AOI) related to potential PFAS releases was identified at the AASF during 

the PA. The AOI is shown on Figure ES-1 and described Table ES-1 below:

Table ES-1: AOI at Rapid City Army Aviation Support Facility

Area of Interest Name Used by Potential Release Date

AOI 1 Overflow Area SDARNG 1999

Based on potential PFAS releases at AOI 1, there is potential for exposure to PFAS contamination 

in media at or near the facility. The preliminary CSM for AOI 1, which presents the potential 

receptors and media impacted, is shown on Figure ES-2. Based on the US Environmental 

Protection Agency (USEPA) Unregulated Contaminant Monitoring Rule 3 (UCMR3) data, it was 

indicated that no PFAS were detected in a public water system above the USEPA lifetime Health 

Advisory within 20 miles of the facility. The HA is 70 parts per trillion for PFOS and PFOA, 

individually or combined. PFAS analyses performed in 2016 had method detection limits that were 

higher than currently achievable. Thus, it is possible that low concentrations of PFAS were not 

detected during the UCMR3 but might be detected if analyzed today.
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Su mmary of Findings

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Area of Interest

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Facility Boundary

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/ /

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Figure ES-2

Preliminary Conceptual Site Model

Rapid City AASF, South Dakota

Potential

Off-Facility

Source Not

under

Control of

ARNG

Notes:

1. The resident and recreational user receptors

refer to an off-facility resident and off-facility

recreational user, respectively.

2. Dermal contact exposure pathway is

incomplete for PFAS.

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1. Introduction

Authority and Purpose

The Army National Guard (ARNG) G9 is the lead agency in performing Preliminary Assessments 

(PAs) and Site Inspections (SIs) for Perfluorooctanesulfonic acid (PFOS) and Perfluorooctanoic 

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

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

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

Order W912DR17F0192, issued 11 August 2017.

The ARNG is assessing potential effects on human health related to processes at facilities that 

used per- and poly-fluoroalkyl substances (PFAS), primarily in the form of aqueous film forming 

foam (AFFF) released as part of firefighting activities, although other PFAS sources are possible. 

In addition, the ARNG is assessing businesses or operations adjacent to the ARNG facility (not 

under the control of ARNG) that could potentially be responsible for a PFAS release. 

PFAS are classified as emerging environmental contaminants that are garnering increasing 

regulatory interest due to their potential risks to human health and the environment. PFAS 

formulations contain highly diverse mixtures of compounds. Thus, the fate of PFAS compounds 

in the environment varies. The regulatory framework at both federal and state levels continues to 

evolve. The US Environmental Protection Agency (USEPA) issued Drinking Water Health 

Advisories for PFOA and PFOS in May 2016, but there are currently no promulgated national 

standards regulating PFAS in drinking water. The HA is 70 parts per trillion for PFOS and PFOA, 

individually or combined. 

This report presents the findings of a PA for PFAS-containing materials at the South Dakota Army 

Aviation Support Facility (AASF; also referred to as the “facility”) in Rapid City, South Dakota, in 

accordance with the Comprehensive Environmental Response, Compensation, and Liability Act 

(CERCLA), as amended, the National Oil and Hazardous Substances Pollution Contingency Plan 

(40 Code of Federal Regulations Part 300), and Army requirements and guidance. 

This PA documents potential locations where PFAS containing materials are stored and have the 

potential to be released into the environment at or adjacent to the AASF. The term PFAS will be 

used throughout this report to encompass all PFAS chemicals being evaluated, including PFOS 

and PFOA, which are key components of AFFF.

Preliminary Assessment Methods

The performance of this PA included the following tasks: 

• Reviewed available administrative record documents and Environmental Data Resources,

Inc. (EDR)TM report packages to obtain information relevant to potential PFAS releases, such

as: drinking water well locations, historical aerial photographs, Sanborn maps, and

environmental compliance actions in the area surrounding the facility;

• Conducted a site visit on 10 September 2019 and completed visual site inspections (VSIs) at

locations where PFAS-containing materials were suspected of being stored, used, or

disposed;

• Interviewed current and retired South Dakota ARNG (SDARNG) personnel, SDARNG

environmental managers, and operations staff;
PFAS Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

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• Completed a visual site inspection at known or suspected potential PFAS release locations

and documented with photographs;

Report Organization

This report has been prepared in accordance with the USEPA Guidance for Performing 

Preliminary Assessments under CERCLA (USEPA, 1991). The report sections and descriptions 

of each are:

• Section 1 – Introduction: identifies the project purpose and authority and describes the

facility location, environmental setting, and methods used to complete the PA

• Section 2 – Fire Training Areas: describes the fire training areas (FTAs) at the facility

identified during the site visit

• Section 3 – Non-Fire Training Areas: describes other locations of potential PFAS releases

at the facility identified during the site visit

• Section 4 – Emergency Response Areas: describes areas of potential PFAS release at the

facility, specifically in response to emergency situations

• Section 5 – Adjacent Sources: describes sources of potential PFAS release adjacent to the

facility that are not under the control of ARNG

• Section 6 – Preliminary Conceptual Site Model: describes the pathways of PFAS transport

and receptors for the Areas of Interest (AOIs) and the facility

• Section 7 –Conclusions: summarizes the data findings and presents the conclusions of the

PA

• Section 8 – References: provides the references used to develop this document

• Appendix A – Data Resources

• Appendix B – Preliminary Assessment Documentation

• Appendix C – Photographic Log

Facility Location and Description

The AASF is in Pennington County, approximately 10 miles southeast of Rapid City, South Dakota

and approximately 8 miles south of Ellsworth Air Force Base (AFB) (Figure 1-1). The AASF is 

adjacent to Rapid City Regional Airport. The facility is accessible from FAA Road from the north 

and Guard Road from the south. 

The AASF is constructed on approximately 38 acres of land owned by the City of Rapid City and 

has been leased to the State of South Dakota Department of Military and Veterans Affairs since 

1957 for a term of 99 years (Appendix A). AASF includes several hangars, storage buildings, 

and administrative offices. 

Facility Environmental Setting

The AASF lies within the Black Hills region, which is characterized as an isolated eroded mountain 

region; ancient rock removal by stream erosion produces this mountain setting. From a distance, 

the rounded hilltops, well-forested slopes, and deep valleys present a dark appearance, giving 

them their name. Rapid Creek is the main stream channel near the facility. 
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1.5.1 Geology

The AASF lies within the eastern side of the Black Hills on an elliptically shaped dome created by 

the tectonic movement during the Laramide Orogeny. During the movement, the tectonic plates 

uplifted crystalline rocks along with exposing the overlying Mesozoic and Paleozoic rock. Beneath 

the complex lays Precambrian-age crystalline basement rocks that are overlain by Cambrian 

through Lower Cretaceous deposits of dolomite, limestone, and sandstone. Within the Upper 

Cretaceous lies deposits of aged marine shales intertwined with beds of limestone and sandstone. 

This aged marine shale has a range from the surface of the AASF down to 1,000 feet below the 

surface. This shale is known as Pierre Shale and forms the bedrock of the complex. 

Pierre Shale located on the complex can be found as a light gray to dark gray, fragmented, 

organic-rich shale. The material is also noncalcic and can be easily changed by weathering, which 

will result in a color change into an orange or brown material. Within the shale, bentonite beds 

can be found, and ironstone layers consist of roughly 1 foot thick. On the weathered parts of the 

Pierre Shale selenite crystals and ironstone nodules can be found. Pierre Shale can be found up 

to depths of 40 feet, but at places of weathering, the depths will be shorter (Aerostar, 2019). 

1.5.2 Hydrogeology

The AASF is in the Black Hills area, which is an important recharge area for aquifers within the 

northern Great Plains. The AASF is within the Williston Basin, which flows into the Madison and 

Minnelusa aquifers. These aquifers are a part of the Paleozoic group, which occurs in areas that 

have high altitude and in uplifts like the Laramide Orogeny in the Black Hills. The Madison aquifer, 

also known as the Mississippian aquifer, has a siltstone, sandstone, limestone, and dolomite 

base. The water found in this location is typically in outcrop areas and flows to the recharge areas 

to the northeast. The discharge location occurs as a result of upward leakage to the lower 

Cretaceous aquifer located in central South Dakota. The Minnelusa aquifer has a limestone and 

sandstone base, and the aquifer moves from areas of recharge to the northeast much like the 

Madison aquifer does. A portion of the water will discharge upward by leakage into the lower 

Cretaceous aquifer. Sandstone composes the lower Cretaceous aquifer and is confined by shale 

except in areas where uplift can be found. Over one-half of the water found in these areas is 

moderately saline and can be described as briny in many parts. The salination of this water occurs 

from upward leakage of mineralized water from the Paleozoic aquifers (US Geological Survey, 

2002). 

No potable water wells are located within the boundary of the AASF; however, monitoring wells, 

and numerous domestic and stock wells are located within 1 to 2 miles of the facility (Figure 1-

2). Depth to groundwater near the facility is approximately 20 feet below ground surface. Drinking 

water for the AASF is supplied by the Rapid City Water Division, which uses the Jackson Springs 

Gallery and the Girl Scouts Gallery as infiltration galleries along the Rapid Creek alluvium. Water 

is also drawn from the Minnelusa and Madison aquifers through eight wells. Surface water collects 

in the Rapid Creek, which collects water from the Deerfield and Pactola Reservoirs. This surface 

water supplies water for treatment to the Mountain View and Jackson Springs treatment plants 

then used for municipal use (Rapid City Water Division, 2018).

Based on the USEPA Unregulated Contaminant Monitoring Rule 3 data, it was indicated that no 

PFAS were detected in a public water system above the USEPA Health Advisory level within 20 

miles of the facility. PFAS analyses performed in 2016 had method detection limits that were 

higher than currently achievable. Thus, it is possible that low concentrations of PFAS were not 

detected during the UCMR3 but might be detected if analyzed today. 
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1.5.3 Hydrology 

An Environmental Data Resources, Inc. (EDR)TM report conducted a well search for a 1-mile 

radius surrounding the facility (Appendix A). Using additional online resources, such as state and 

local GIS databases, wells were researched to a 4-mile radius of the facility. The AASF has a 

streamflow that is influenced depending on the climate at the time and the geologic conditions. 

The base flow in Rapid City comes from the higher altitudes surrounding the city and occurs from

events of high precipitation. Many of the surrounding streams have headwater springs that 

originate from the Paleozoic carbonate rocks. These streams generally flow eastward over the 

Precambrian rocks of the crystalline core and typically lose flow as the Paleozoic rock dissipates 

out of the Black Hills (US Geological Survey, 2002). Surface water at the facility flows south to 

southeast to unnamed tributaries of Rapid Creek (Figure 1-3).

1.5.4 Climate 

The climate at the AASF consists of four clearly separated seasons, with warm and clear summers 

and dry, freezing, cloudy, windy winters. Temperatures vary from average highs of 59.1 degrees 

Fahrenheit (°F) to average lows of 33.5 °F. The average annual temperature is 46.3 °F. Average 

precipitation is 18.32 inches of rain (World Climate, 2019).

1.5.5 Current and Future Land Use

The AASF is a controlled access facility with public roads and is adjacent to Rapid City Municipal 

Airport. The facility consists of an administration building and office areas. Exterior features are 

vehicle parking areas and roads. Infrastructure improvements, land acquisitions, land use 

controls, and reasonably anticipated future land use is not expected to change from the current 

land use.
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PFAS Preliminary Assessment Report

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2. Fire Training Areas

No FTAs were identified within the facility during the PA through interviews or document review. 

Fire training exercises for the SDARNG were conducted at Ellsworth AFB. 
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3. Non-Fire Training Areas

In addition to FTAs, the PA evaluated areas where PFAS-containing materials may have been 

broadly used, stored, or disposed. This may include buildings with fire suppression systems, paint 

booths, AFFF storage areas, and areas of compliance demonstrations. Information on these 

features obtained during the PA are included in Appendices A and B. Three non-FTAs were

identified within the AASF facility during the PA through interviews or document review. A 

description of the non-FTAs is presented below and shown on Figure 3-1. Interview records and 

photographs are included in Appendix B and Appendix C, respectively. 

Main Hangar

The Main Hangar was constructed in 1999 by the SDARNG. The geographic coordinates of the 

hangar are 44°2'13.20"N; 103°3'29.23"W. The hangar fire suppression system consists of two

1,100-gallon tanks filled with 3 percent AFFF concentrate. The AFFF tanks that supply the fire 

suppression system are housed in a separate room, adjacent to the hangar. When the fire 

suppression system is engaged, an automatic switch is activated that routes the AFFF foam/water 

mixture from the trench drains to a 3,000-gallon concrete bypass underground storage tank 

(UST). When the fire suppression system is not engaged, liquid in the trench drains is routed to 

an oil/water separator, which discharges to a lagoon on the south side of the runway. The bypass 

UST is located on the southwest side of the hangar. 

The fire suppression system was installed and initially tested in December of 1999 by a contractor.

A firehose was connected to the test header port just inside the hangar, and a foam/water mixture 

was allowed to flow through the firehose to a large plastic container where the mixture was 

analyzed. During this test, the large plastic container over-flowed and the foam/water mixture 

spilled onto the concrete. The contractor addressed the spill immediately; however, a small 

amount of the mixture flowed into the grassy area south of the Main Hangar. The plastic container 

held approximately 500 gallons of the foam/water mixture, which was taken off site for disposal

by the contactor. 

Since 2002, the fire suppression system has been tested annually, to ensure the fire suppression 

system is functional. The contractor uses a hose to bypass the hangar and empties approximately 

500-gallons of the AFFF foam/water mixture directly into the bypass UST. When the bypass UST

becomes full, a contractor removes the AFFF foam/water mixture. The AFFF foam/water mixture

is applied to the Municipal Solid Waste Compost at the Rapid City Landfill to prevent fires. Based

on records, approximately 1,500 gallons of the AFFF foam/water mixture was disposed five times,

with the first occurring on January 6, 2006. The remaining disposals occurred at approximate

three-year intervals. In 2019, the AFFF foam/water mixture was disposed of through a Defense

Logistics Agency (DLA) contract. The AFFF foam/water mixture is no longer taken to the Rapid

City Landfill. There are no reported leaks or releases from bypass the UST since installation;

however, the bypass UST does not have a leak detection system.

There are six mobile Halon fire extinguishers that have been located on the aircraft ramp since 

1987. Prior to 2005, non-AFFF fire extinguishers were used on the flight line and ramp areas.

In Spring of 2016, a portion of the concrete and grassy areas southwest of the Main Hangar were 

excavated to make the drainage ditch deeper to allow for better storm water drainage. According 

to personnel, some of the soil that was removed from the area was used as fill soil, when the new 

Readiness Center at the facility began construction in 2019. 
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Old Hangar – Bay 1

There was no fire suppression system in the Old Hangar – Bay 1, which is adjacent to the armory 

building. The geographic coordinates of the Old Hangar – Bay 1 are 44° 2'13.07"N; 103° 

3'29.33"W. 

Cold Storage Hangar

There was no fire suppression system in the Cold Storage Hangar. The geographic coordinates 

of the cold storage hangar are 44° 2'17.84"N; 103° 3'29.26"W. Additional Halon fire extinguishers 

are stored in the Cold Storage Hangar when not in use on the flight line. 
Main Hangar

Cold Storage Hangar

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Non-Fire Training Areas

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4. Emergency Response Areas

No emergency response areas were identified within AASF during the PA through interviews or 

document review. Rapid City Fire Department provides fire emergency services for the AASF. 
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5. Adjacent Sources

Three off-site PFAS sources adjacent to the AASF were identified during the PA through interviews 

and document review (Appendix A and Appendix B). Figure 5-1 presents the location of 

potential AASF adjacent source areas.

Rapid City Fire Department

The Rapid City Fire Department provides emergency response for the AASF. This department is 

an active fire station containing emergency response vehicles and equipment. The Rapid City 

Fire Department is located north and upgradient of AASF, and it is unknown if AFFF is used during 

emergency response actions or training.

Ellsworth AFB

Ellsworth AFB is approximately eight miles north of the AASF. In 2018, a Site Inspection was 

completed at Ellsworth AFB and twelve areas of concern were identified for potential PFAS 

contamination. The medium impacted by PFAS at Ellsworth AFB included surface soil, 

groundwater, surface water, and sediment. The results of the SI indicated PFOA and PFOS 

concentrations above the USEPA HAs in groundwater for nine of twelve areas investigated. 

Additionally, PFOA and PFOS were also detected in surface water and surface soil at four of 

twelve areas investigated. 

Landfills

Landfills are not usually a primary release area of PFAS; however, interviewees indicated that the 

AFFF foam/water mixture from the bypass UST generated during fire suppression system testing 

was solely applied to Municipal Solid Waste Compost at the Rapid City Landfill by a contractor. 

The application of the AFFF foam/water mixture was intended to prevent compost fires. Based on 

records, approximately 1,500 gallons of the AFFF foam/water mixture was disposed five times, 

with the first occurring on January 6, 2006. The remaining disposals occurred at approximate 

three-year intervals. In 2019, the AFFF foam/water mixture was disposed of through a DLA 

contract and incinerated. The Rapid City Landfill is approximately 7 miles to the west of the AASF. 
Iowa Ditch

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Dry Creek

Rapid Cre ek

Cyclone Ditc h

Ellsworth

Airforce Base

Rapid

City Fire

Department

Bypass UST

Lagoon

Murphy Ditch

Rapid

City Fire

Department

0 340 680 1,360

Feet

0 0.75 1.5 3

Miles

­ Figure 5-1

CLIENT

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ARNG

Preliminary Assessment for PFAS at Rapid City AASF, SD

2/19/2020

2/19/2020

2/19/2020

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2/19/2020

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Q:\Projects\ENV\GEARS\GEO\ARNG PFAS\900-CAD-GIS\920-GIS or Graphics\MXD\SD\Rapid_City_AASF_Figures\Fig_5-1_Rapid_City_AASF_Adjacent_Sources.mxd

Adjacent Sources

12420 Milestone Center Drive

Germantown, MD 20876

Potential PFAS Release

Facility Boundary

Water Body

Wetland

River/Stream

Canal/Ditch

17
PFAS Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

18

6. Preliminary Conceptual Site Model

Based on the PA findings, one non-FTA was identified where PFAS may have been incidentally 

spilled to the ground surface: AOI 1 Overflow Area. As such, this area is determined to be an AOI 

and may be a potential PFAS source area. The AOI location is shown in Figure 6-1. 

The following section describes the CSM components and the specific preliminary CSM 

developed for AOI 1. The CSM identifies the three components necessary for a potentially 

complete exposure pathway: (1) source, (2) pathway, (3) receptor. If any of these elements are 

missing, the pathway is considered incomplete. The preliminary CSM for AOI 1 is shown in Figure 

6-2.

AOI 1 Overflow Area

During the first fire suppression system test in December of 1999, a large plastic container overflowed spilling foam/water onto the concrete and a small amount of the mixture flowed into the 

grassy area south of the Main Hangar. 

AFFF releases at AOI 1 occurred on concrete and grassy surfaces. Ground-disturbing activities 

to surface soil at AOI 1 could result in site worker and construction worker exposure to potential 

PFAS contamination; therefore, the exposure pathways for inhalation of soil particles and 

ingestion of soil are potentially complete for these receptors. PFAS releases to surface soil at AOI 

1 may have infiltrated subsurface soil; therefore, the exposure pathways for ingestion of soil is

potentially complete for construction workers. 

Additionally, there are several domestic wells located downgradient within 4-miles of the AASF; 

therefore, the ingestion exposure pathway for groundwater is considered potentially complete for 

off-facility residents. No surface water features flow through AOI 1; therefore, surface water and 

sediment exposure pathways are incomplete. The preliminary CSM for AOI 1 is shown on Figure 

6-2.
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0 150 300 600

Feet

0 0.75 1.5 3

Miles

­ Figure 6-1

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Preliminary Assessment for PFAS at Rapid City AASF, SD

7/7/2020

7/7/2020

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C:\Users\stankevichm\OneDrive - AECOM Directory\ARNG_PFAS_GIS_60552172\MXDs\SD\Rapid_City_AASF_Figures\Fig_6-1_Rapid_City_AASF_AOIs.mxd

Area of Interest

12420 Milestone Center Drive

Germantown, MD 20876

Area of Interest

Potential PFAS Release

No Suspected Release

Facility Boundary

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Wetland

River/Stream

Canal/Ditch

Surface Water Flow

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19
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/ / /

Figure 6-2

Preliminary Conceptual Site Model

AOI 1 Overflow Area

Potential

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under

Control of

ARNG

Notes:

1. The resident and recreational user receptors

refer to an off-facility resident and off-facility

recreational user, respectively.

2. Dermal contact exposure pathway is

incomplete for PFAS.

/

/ /

/ / / /

/ / / /

/

/ /

/

20
PFAS Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

21

7. Conclusions

This report presents a summary of available information gathered during the PA on the use and 

storage of AFFF and other PFAS-related activities at the AASF. The PA findings are based on the 

information presented in Appendix A and Appendix B. 

Findings

One AOI related to a potential PFAS release was identified (Table 7-1) at the AASF during the PA 

(Figure 7-1). 

Table 7-1: AOI at Rapid City Army Aviation Support Facility

Area of Interest Name Used by Potential Release Dates

AOI 1 Overflow Area SDARNG 1999

Based on potential PFAS releases at AOI 1, there is potential for exposure to PFAS contamination 

in media at or near the facility. The preliminary CSM for AOI 1 is shown on Figure 6-2, which 

presents the potential receptors and media impacted. One off-facility source located 

approximately 8 miles north of the AASF was identified as a potential PFAS source during the PA 

(Figure 7-1). The US Air Force is currently completing investigations at Ellsworth AFB. 

Groundwater surrounding the AASF is inferred to flow to the south toward Rapid Creek. 

The following areas, which were discussed in Section 3, were determined to have no suspected 

PFAS releases (Table 7-2).

Table 7-2: No Suspected Release Areas

No Suspected Release 

Area Used by Rationale for No Suspected Release Determination

Old Hangar – Bay 1 SDARNG The hangar has never had a fire suppression 

system, or AFFF fire extinguishers.

Cold Storage Hangar SDARNG The hangar has never had a fire suppression 

system, or AFFF fire extinguishers.

Main Hangar SDARNG

During annual fire suppression system testing this 

hose is directly connected to the bypass UST and no 

AFFF has been dispensed into the Main Hangar. 

Uncertainties

A number of information sources were investigated during this PA to determine the potential for 

PFAS-containing materials to have been present, used, or released at the facility. Historically, 

documentation of PFAS use was not required because PFAS were considered benign. Therefore, 

records were not typically kept by the facility or available during the PA on the use of PFAS in 

training, firefighting, or other non-traditional activities, or on its disposition. 

The conclusions of this PA are based on all available information, including: previous 

environmental reports, EDRsTM, observations made during the VSI, and interviews. Interviews of 

personnel with direct knowledge of a facility generally provided the most useful insights regarding 

a facility's historical and current PFAS-containing materials. Sometimes, the provided information 

was vague or conflicted with other sources. Gathered information has a degree of uncertainty due 
PFAS Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

22

to the absence of written documentation, the limited number of personnel with direct knowledge 

due to staffing changes, the time passed since PFAS were first used (1969 to present), and a 

reliance on personal recollection. Inaccuracies may arise in potential PFAS release locations, 

dates of release, volume of releases, and the concentration of AFFF used. There is also a 

possibility the PA has missed a source of PFAS, as the science of how PFAS may enter the 

environment continually evolves.

In order to minimize the level of uncertainty, readily available data regarding the use and storage 

of PFAS were reviewed, retired and current personnel were interviewed, multiple persons were 

interviewed for the same potential source area, and potential source areas were visually 

inspected. Table 7-3 summarizes the uncertainties associated with the PA. 

Table 7-3: Uncertainties

Area of Interest Source of Uncertainty

AASF Potential off-facility PFAS release areas exist adjacent to the AASF. 

Because these areas include property upgradient of the facility, it is 

unknown whether or not the off-facility sources affect the AASF.

AOI 1 The integrity of the bypass UST is unknown.

AOI 1 The foam/water mixture generated from the initial fire suppression 

system test was disposed of by the contractor. It is unknown where the 

contractor disposed of the mixture. 

Potential Future Actions

Interviews and records (covering 1982 to present) indicate that ARNG activities may have resulted 

in a potential PFAS release at the one AOI identified during the PA. Based on the preliminary CSM 

developed for the AOI, there is potential for receptors to be exposed to PFAS contamination in 

media at or near the facility. Table 7-4 summarizes the rationale used to determine if the AOI 

should be considered for further investigation under the CERCLA process and undergo an SI. 

ARNG will evaluate the need for an SI at the AASF based on the potential receptors, the potential 

migration of PFAS contamination off the facility, and the availability of resources. 

Table 7-4: PA Findings Summary

Area of Interest AOI Location Rationale Potential Future Action

AOI 1 Overflow 

Area

44° 2'13.33"N; 

103° 3'31.44"W

One-time fire suppression 

system test that resulted in 

a small amount of AFFF 

overflowing onto the 

concrete and grassy area 

to the south of the Main 

Hangar. 

Proceed to SI, focus on 

soil and groundwater. 
Iowa Ditch

HawthorneDitc h

Murphy Dti

c h

B oxeld er Cree k

Dry Creek

Rapid Cre ek

Cyclone Ditc h

Ellsworth

Airforce Base

Rapid

City Fire

Department

Lagoon

Main Hangar

Cold Storage Hangar

Old Hangar – Bay 1

Rapid

City Fire

Department

Overflow Area

AOI 1

Bypass UST

0 150 300 600

Feet

0 0.75 1.5 3

Miles

­ Figure 7-1

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Preliminary Assessment for PFAS at Rapid City AASF, SD

7/7/2020

7/7/2020

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7/7/2020

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C:\Users\stankevichm\OneDrive - AECOM Directory\ARNG_PFAS_GIS_60552172\MXDs\SD\Rapid_City_AASF_Figures\Fig_7-1_Rapid_City_AASF_Summary.mxd

Summary of Findings

12420 Milestone Center Drive

Germantown, MD 20876

Area of Interest

Potential PFAS Release

No Suspected Release

Facility Boundary

Water Body

Wetland

River/Stream

Canal/Ditch

23
PFAS Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

24

8. References

Aerostar SES LLC (Aerostar). 2019. Final Site Inspections Report of Aqueous Film Forming 

Form Areas at Ellsworth Air Force Base, Meade and Pennington Counties, South Dakota.

November. 

Rapid City Water Division. 2018. Annual Water Quality Report. November.

United States Environmental Protection Agency (USEPA). 1991. Guidance for Performing 

Preliminary Assessments under CERCLA. September.

United States Geological Survey. 2002. Hydrology of the Black Hills Area, South Dakota. 

November. 

World Climate. 2019. Available at http://www.worldclimate.com/climate/us/south-dakota/rapidcity (Accessed November 12, 2019).
PFAS Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

Appendix A 

Data Resources
PFAS Preliminary Assessment Report

Rapid City AASF, Rapid City, 

Data Resources will be provided separately on CD. Data Resources for Rapid City AASF.

Rapid City AASF Leases, Licenses, and Permits

• 2001 Lease Information

Rapid City AASF Documentation

• 2015 Final Preliminary Assessment Report For Perfluorinated Compounds at Ellsworth Air

Force Base South Dakota

• 2019 Final Site Inspection Report of Aqueous Film Forming Foam Areas at Ellsworth Air

Force Base Meade and Pennington Counties, South Dakota

EDR Report

• 2019 Rapid City AASF EDRTM Report
PFAS Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

Appendix B 

Preliminary Assessment Documentation
PFAS Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

Appendix B.1 

Interview Records










PA Interview Questionnaire - Other Facility: Rapid City AASF

Interviewer: 

Date/Time: 9/10/19 at 1000

Interviewee: 

Title: Fire Emergency Services Manager

Phone Number:

Email: 

Can your name/role be used in the PA Report? Y or 

N 

Can you recommend anyone we can interview?

Y or N __________________________ 

Roles or activities with the Facility/Years working at the Facility:

Fire Emergency Services Manager- 2 years at the facility

PFAS Use: Identify accidental/intentional release locations, time frame of release, frequency of 

releases, storage container size (maintenance, fire training, firefighting, buildings with suppression 

systems (as builts), fueling stations, crash sites, pest management, recreational, dining facilities, 

metals plating, or waterproofing). How are materials ordered/purchased/disposed/shared with others?

• No record of sanctioned fire training events

• No municipal crashes or airport crashes

• No emergency response to airport or AASF

Known Uses

Use 

Procurement

Disposition

Storage (Mixed)

Storage (Solution)

Inventory, Off-Spec

Containment

SOP on Filling

Leaking Vehicles

Nozzle and 

Suppression System 

Testing

Dining Facilities

Vehicle Washing

Ramp Washing

Fuel Spill Washing

and Fueling Stations

Chrome Plating or 

Waterproofing
PA Interview Questionnaire - Other Facility: Rapid City AASF

Interviewer: 

Date/Time: 4/13/2020 at 1000

Interviewee: 

Title: 

Phone Number:

Email: 

Can your name/role be used in the PA Report? Y or 

N 

Can you recommend anyone we can interview? 

Y or N __________________________ 

Roles or activities with the Facility/Years working at the Facility:

PFAS Use: Identify accidental/intentional release locations, time frame of release, frequency of 

releases, storage container size (maintenance, fire training, firefighting, buildings with suppression 

systems (as builts), fueling stations, crash sites, pest management, recreational, dining facilities, 

metals plating, or waterproofing). How are materials ordered/purchased/disposed/shared with others?

• First Fire Suppression System Testing: 

o During the first fire suppression system test in December of 

1999, a contractor connected a firehose to the test header port 

just inside the hangar, and foam/water was allowed to flow 

through the firehose to a large plastic container where the foam 

mixture was analyzed. During this test, the large plastic 

container over-flowed spilling foam/water onto the concrete and 

a small amount of AFFF traveled to the grass area outside the 

hangar. The majority of the AFFF that over-flowed was swept 

up by the contractor and the approximate 500 gallons of AFFF 

were taken off site for disposal.

Known Uses

Use 

Procurement

Disposition

Storage (Mixed)

Storage (Solution)

Inventory, Off-Spec

Containment

SOP on Filling

Leaking Vehicles

Nozzle and 

Suppression System 

Testing

Dining Facilities

Vehicle Washing

Ramp Washing

Fuel Spill Washing

and Fueling Stations

Chrome Plating or 

Waterproofing
PA Interview Questionnaire - Other Facility: Rapid City AASF

Interviewer: 

Date/Time: 9/10/19 at 10:00

Interviewee: 

Title: Maintenance

Phone Number:

Email:

Can your name/role be used in the PA Report? Y or 

N 

Can you recommend anyone we can interview?

Y or N __________________________ 

Roles or activities with the Facility/Years working at the Facility:

Maintenance, 16 years at the facility

PFAS Use: Identify accidental/intentional release locations, time frame of release, frequency of 

releases, storage container size (maintenance, fire training, firefighting, buildings with suppression 

systems (as builts), fueling stations, crash sites, pest management, recreational, dining facilities, 

metals plating, or waterproofing). How are materials ordered/purchased/disposed/shared with others?

• New Hangar

o Fire suppression system installed in 1999

o Equipped with two, 1,100-gallon 3% AFFF tanks

o Bypass tank: when the fire alarm is activated, an automatic 

switch causes the trench drains in the hangar to go to a holding 

tank to capture the AFFF foam/water mixture. The bypass tank 

holds 3000-gallons and is underground, on the southwest side 

of the hangar. The pathway of all the drains is to the oil/water 

separator, then to a lagoon on the south side of the airstrip. The 

tank is made of concrete and there are no reports of any 

leaking.

o When the tank is full, they pump contents into a truck and it is 

sprayed on an unknown landfill to help prevent any landfill 

fires

• Fire Suppression Testing (New Hangar)

o October 28th, 1999: the fire suppression system was engaged 

and flowed with foam. The AFFF foam/water mixture went 

down the trench drains and into the bypass UST.

o August 2002: annual maintenance to present 

 Conducted via contractor where testing occurs directly 

from the suppression system (bypassing sprinklers) and 

empties approximately 500-gallons and directly 

dispenses into the bypass underground tank via hose. 

• Mobile Fire extinguishers have been 6 Halon extinguishers since 1987. 

Information on fire extinguishers prior to then is unknown. 

• Old hangar (armory) does not have a fire suppression system 

• No bulk AFFF has been stored at the AASF, they wait to order AFFF 

concentrate until they can fill it up with the entire amount ordered.

Known Uses

Use 

Procurement

Disposition

Storage (Mixed)

Storage (Solution)

Inventory, Off-Spec

Containment

SOP on Filling

Leaking Vehicles

Nozzle and 

Suppression System 

Testing

Dining Facilities

Vehicle Washing

Ramp Washing

Fuel Spill Washing

and Fueling Stations

Chrome Plating or 

Waterproofing
PA Interview Questionnaire - Other Facility: Rapid City AASF

Interviewer: Savannah Irving

Date/Time: 9/10/19 at 10:00

• All surface water and groundwater flow towards the lagoon south of the 

runway 
PFAS Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

Appendix B.2 

Visual Site Inspection Checklists
Visual Site Inspection Checklist

Names(s) of people performing VSI:

Recorded by:

ARNG Contact:

Date and Time: 9/10/2019 10am

Method of visit (walking, driving, adjacent): walking, driving

Source/Release Information

Site Name / Area Name / Unique ID: Rapid City AASF 

approximately 39 acres

Historic Site Use (Brief Description):

Current Site Use (Brief Description):

Physical barriers or access restrictions: 

1. Was PFAS used (or spilled) at the site/area? Y / N

1a. If yes, document how PFAS was used and usage time (e.g., fire fighting training 2001 to 2014):

2. Has usage been documented? Y / N

2a. If yes, keep a record (place electronic files on a disk): 

3. What types of businesses are located near the site? Industrial / Commercial / Plating / Waterproofing / Residential

3a. Indicate what businesses are located near the site

4. Is this site located at an airport/flightline? Y / N

4a. If yes, provide a description of the airport/flightline tenants:

Site / Area Acreage:

The original portion (11.48 acres) of the 38.88 acre property was acquired in 1957, 

and the hanger was built in 1959. In 1999, a new AASF shop facility was 

constructed. The facility consists of a storage hangar, repair hangar, shops, and a two 

story office area. Exterior features are vehicle parking areas, roads, aircraft parking 

and taxiways. 

The AASF supports the South Dakota Army National Guard (SDARNG). 

Access to the area is restricted to SDARNG. 

Hangar fire suppression system dispensed foam in 1999, 2002-present roughly 500-gallon test release 

annually. The first release of the environemnt through the pumping of the bypass tank was January, 6th, 

2006. 

Documented in interview documents.

Rapid City Municipal Airport, and residental are adjacent. 

Rapid City Municipal Airport.

Page 1 of 4
Visual Site Inspection Checklist

1. Does the facility have a fire suppression system? Y / N

1a. If yes, indicate which type of AFFF has been used:

1b. If yes, describe maintenance schedule/leaks:

1c. If yes, how often is the AFFF replaced:

1d. If yes, does the facility have floor drains and where do they lead? Can we obtain an as built drawing?

Transport / Pathway Information

1. Does site/area drainage flow off installation? Y / N

1a. If so, note observation and location:

Surface water flows to the south to the Rapid Creek which travels east to the Cheyenne River.

2. Is there channelized flow within the site/area? Y / N

2a. If so, please note observation and location: 

3. Are monitoring or drinking water wells located near the site? Y / N

3a. If so, please note the location: 

4. Are surface water intakes located near the site? Y / N

4a. If so, please note the location: 

5. Can wind dispersion information be obtained? Y / N

5a. If so, please note and observe the location.

N/A

6. Does an adjacent non-ARNG PFAS source exist? Y / N

6a. If so, please note the source and location.

6b. Will off-site reconnaissance be conducted? Y / N

There are 26 domestic wells and 8 monitoring wells are located within 2 miles of the site.

Murphy Ditch is located less than one mile south of the AASF and Rapid Creek is located two miles south of 

the facility.

Yes, Rapid City Fire Department and Ellsworth AFB are potential sources of PFAS ajacent to the AASF. 

Other Significant Site Features: 

Migration Potential:

The fire suppression systems have 3% AFFF tanks.

Hangar fire suppression system dispensed foam in 1999, 2002-present roughly 500-gallon test release 

annually.

The fire suppression systems have two 1,100 gallon tanks with 3% AFFF.

The floor drains lead to an oil/water separator then to a lagoon on the south side of the airstrip. Yes, there are 

as-builts for the fire suppression system. 

Page 2 of 4
Visual Site Inspection Checklist

1. Has the infrastructure changed at the site/area? Y / N

1a. If so, please describe change (ex. Structures no longer exist): 

In 1999 the new AASF hangars were built.

2. Is the site/area vegetated? Y / N

2a. If not vegetated, briefly describe the site/area composition:

3. Does the site or area exhibit evidence of erosion? Y / N

3a. If yes, describe the location and extent of the erosion: 

4. Does the site/area exhibit any areas of ponding or standing water? Y / N

4a. If yes, describe the location and extent of the ponding: 

Receptor Information

1. Is access to the site restricted? Y / N

1a. If so, please note to what extent:

2. Who can access the site? 

2a. Circle all that apply, note any not covered above: 

3. Are residential areas located near the site? Y / N

3a. If so, please note the location/distance: 

Residents to the south and west

4. Are any schools/day care centers located near the site? Y / N

4a. If so, please note the location/distance/type: 

5. Are any wetlands located near the site? Y / N

5a. If so, please note the location/distance/type: 

Significant Topographical Features: 

Site Workers / Construction Workers / Trespassers / Residential / Recreational 

Users / Ecological

The facility has controlled access

Page 3 of 4
Visual Site Inspection Checklist

Additional Notes

Photographic Log

Photo ID/Name

1

2

3

4

5

AFFF fire suppression system sprinkler system located in the 

hangar. 

Date & Location

9/10/19, located inside a room in 

the hangar

Halon and dry chem ABC mobile fire extinguishers used on the 

flight line. 

Mobile Halon fire extinguisher used on the flight line. 9/10/19, located inside a room in 

the hangar

9/10/19, located inside a room in 

the hangar

9/10/19, located inside a room in 

the hangar

9/10/19, located north of the 

hangar

Photograph Description

The near manholes lead to the bypass tank while the far pair of 

manholes leads to the oil/water separator.

There are the two 1,100-gallon tanks that hold 3% AFFF 

concentrate that supplies the hangar.

Page 4 of 4
PFAS Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

Appendix B.3 

Conceptual Site Model Information
Preliminary Assessment – Conceptual Site Model Information

Site Name: Rapid City Army Aviation Support Facility 

Why has this location been identified as a site?

Facility is an aviation support site with an aircraft hangar, high probability of release due to asset type 

and historical site usage. 

Are there any other activities nearby that could also impact this location?

Yes, the potential adjacent sources include the Rapid City Fire Department at Rapid City Regional 

Airport and Ellsworth Air Force Base.

Training Events

Have any training events with AFFF occurred at this site? No

If so, how often? N/A

How much material was used? Is it documented? N/A

Identify Potential Pathways: Do we have enough information to fully understand over land surface 

water flow, groundwater flow, and geological formations on and around the facility? Any direct 

pathways to larger water bodies? 

Surface Water:

Surface water flow direction? To the south towards the Rapid Creek

Average rainfall? 18.32 inches

Any flooding during rainy season? unknown

Direct or indirect pathway to ditches? Direct

Direct or indirect pathway to larger bodies of water? Indirect to Rapid Creek; Rapid Creek discharges to

Cheyenne River.

Does surface water pond any place on site? No

Any impoundment areas or retention ponds? No

Any NPDES location points near the site? unknown

How does surface water drain on and around the flight line? Around the flight line, the surface water 

ultimately drains south to Rapid Creek.

Groundwater:

Groundwater flow direction? To the south towards Rapid Creek

Depth to groundwater? unknown

Uses (agricultural, drinking water, irrigation)? Not used.

Any groundwater treatment systems? No

Any groundwater monitoring well locations near the site? Yes

Is groundwater used for drinking water? Drinking water is supplied by the Rapid City Water Division, 
Preliminary Assessment – Conceptual Site Model Information

which receives water from groundwater sources.

Are there drinking water supply wells on installation? No

Do they serve off-post populations? No

Are there off-post drinking water wells downgradient? No potable water wells are located within the 

boundary of the AASF; however, wells exist within one mile of the facility.

Waste Water Treatment Plant:

Has the installation ever had a WWTP, past or present? No

If so, do we understand the process and which water is/was treated at the plant? N/A

Do we understand the fate of sludge waste? N/A

Is surface water from potential contaminated sites treated? N/A

Equipment Rinse Water

1. Is firefighting equipment washed? Where does the rinse water go?

No

2. Are nozzles tested? How often are nozzles tested? Where are nozzles tested? Are nozzles cleaned after 

use? Where does the rinse water flow after cleaning nozzles?

No

3. Other? 

Firefighting services for the AASF are provided by the Rapid City Fire Department.

Identify Potential Receptors: 

Site Worker Yes

Construction Worker Yes

Recreational User No

Residential No

Child No

Ecological No

Note what is located near by the site (e.g. daycare, schools, hospitals, churches, agricultural, livestock)?

Residential area is within one mile of the facility.

Documentation 

Ask for Engineering drawings (if applicable). Has there been a reconstruction or changes to the drainage 

system? When did that occur? The AASF has a drainage system, where surface water drains to Rapid

Creek, then flows into the Cheyenne River.
PFAS Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

Appendix C 

Photographic Log
Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

Perfluorooctane-Sulfonic Acid (PFOS) and 

Perfluorooctanoic Acid (PFOA) Impacted Sites

ARNG Installations, Nationwide

AECOM

APPENDIX C – Photographic Log

Army National Guard, Preliminary

Assessment for PFAS Rapid City AASF South Dakota

Photograph No. 1

Description:

The near manholes lead to the 

bypass tank while the far pair 

of manholes leads to the

oil/water separator. 

Photograph No. 2

Description:

AFFF fire suppression system 

sprinkler system located in the 

hangar. 
Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

Perfluorooctane-Sulfonic Acid (PFOS) and 

Perfluorooctanoic Acid (PFOA) Impacted Sites

ARNG Installations, Nationwide

AECOM

APPENDIX C – Photographic Log

Army National Guard, Preliminary

Assessment for PFAS Rapid City AASF South Dakota

Photograph No. 3

Description:

These are the two 1,100-

gallon tanks that hold 3% 

AFFF concentrate that 

supplies the hangar fire 

suppression system.

Photograph No. 4

Description: 

Mobile Halon fire 

extinguisher used on the flight 

line. 
Preliminary Assessment Report

Rapid City AASF, Rapid City, South Dakota

Perfluorooctane-Sulfonic Acid (PFOS) and 

Perfluorooctanoic Acid (PFOA) Impacted Sites

ARNG Installations, Nationwide

AECOM

APPENDIX C – Photographic Log

Army National Guard, Preliminary 

Assessment for PFAS Rapid City AASF South Dakota

Photograph No. 5

Description:

Halon and dry chem ABC

mobile fire extinguishers used 

on the flight line.