FINAL

Site Inspection Report 

Mather Army Aviation Support 

Facility

Sacramento, California

Site Inspection for Perfluorooctanoic acid (PFOA), 

Perfluorooctanesulfonic acid (PFOS), Perfluorohexanesulfonic 

acid (PFHxS), Perfluorononanoic acid (PFNA), 

Hexafluoropropylene oxide dimer acid (HFPO-DA), and 

Perfluorobutanesulfonic acid (PFBS) at ARNG Installations, 

Nationwide 

September 2023 

Prepared for:

Army National Guard Bureau

111 S. George Mason Drive

Arlington, VA 22204

UNCLASSIFIED
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Table of Contents

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

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

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

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

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

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

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

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

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

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

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

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

2.2.6 Sensitive Habitat and Threatened/ Endangered Species.............................2-3

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

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

3.1 AOI 1 Wash Rack..................................................................................................3-1

3.2 AOI 2 Airfields and AFFF Storage Areas................................................................3-1

3.3 AOI 3 ARNG and Air Force FTA #1........................................................................3-1

3.4 AOI 4 ARNG and Air Force FTA #2........................................................................3-1

3.5 AOI 5 ARNG and Air Force FTA #3........................................................................3-1

3.6 Adjacent Sources ..................................................................................................3-2

3.6.1 Former Mather Air Force Base ....................................................................3-2

3.6.2 Elite Air Interiors..........................................................................................3-3

3.6.3 Fire Training Area........................................................................................3-3

3.6.4 California Department of Forestry and Fire Protection.................................3-3

3.6.5 Mather Aircraft Rescue and Firefighting ......................................................3-3

3.6.6 Emery Worldwide Flight 17 Crash ...............................................................3-4

3.6.7 Air Force B-52 Bomber Crash .....................................................................3-4

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

5.6 Investigation-Derived Waste..................................................................................5-4
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5.7 Laboratory Analytical Methods ..............................................................................5-5

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

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

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

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

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

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

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

6.3.3 AOI 1 Conclusions ......................................................................................6-3

6.4 AOI 2.....................................................................................................................6-3

6.4.1 AOI 2 Soil Analytical Results .......................................................................6-3

6.4.2 AOI 2 Groundwater Analytical Results.........................................................6-3

6.4.3 AOI 2 Conclusions ......................................................................................6-4

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

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

6.5.2 AOI 3 Groundwater Analytical Results.........................................................6-4

6.5.3 AOI 3 Conclusions ......................................................................................6-4

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

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

6.6.2 AOI 4 Groundwater Analytical Results.........................................................6-5

6.6.3 AOI 4 Conclusions ......................................................................................6-5

6.7 AOI 5.....................................................................................................................6-5

6.7.1 AOI 5 Soil Analytical Results .......................................................................6-6

6.7.2 AOI 5 Groundwater Analytical Results.........................................................6-6

6.7.3 AOI 5 Conclusions ......................................................................................6-6

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

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

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

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

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

7.1.4 AOI 4...........................................................................................................7-2

7.1.5 AOI 5...........................................................................................................7-2

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

7.2.1 AOI 1 through AOI 5....................................................................................7-3

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

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

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

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

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

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

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

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

Appendix A Data Usability Assessment and Validation Reports

Appendix B Field Documentation

B1. Log of Daily Notice of Field Activities

B2. Sampling and Well Development Forms

B3. Field Change Request Forms

B4. Nonconformance and Corrective Action Reports

B5. Survey Data

Appendix C Photographic Log

Appendix D TPP Meeting Minutes

Appendix E Boring Logs and Well Construction Forms

Appendix F Analytical Results

Appendix G Laboratory Reports

Figures

Figure 2-1 Facility Location

Figure 2-2 Facility Topography

Figure 2-3 Groundwater Features

Figure 2-4 Groundwater Elevations, April 2022

Figure 2-5 Surface Water Features

Figure 3-1 Areas of Interest

Figure 5-1 Site Inspection Sample Locations

Figure 6-1 PFOA Detections in Soil

Figure 6-2 PFOS Detections in Soil

Figure 6-3 PFBS Detections in Soil

Figure 6-4 PFHxS Detections in Soil

Figure 6-5 PFNA Detections in Soil

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

Figure 6-7 PFHxS and PFNA Detections in Groundwater

Figure 7-1 Conceptual Site Model, AOI 1 through AOI 4

Figure 7-2 Conceptual Site Model, AOI 5

Tables

Table ES-1 Screening Levels (Soil and Groundwater)

Table ES-2 Summary of Site Inspection Findings and Recommendations

Table 5-1 Site Inspection Samples by Medium

Table 5-2 Soil Boring Depths

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

Table 6-1 Screening Levels (Soil and Groundwater)

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

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

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

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

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

% percent

°C degrees Celsius

°F degrees Fahrenheit

μg/kg micrograms per kilogram

AASF Army Aviation Support Facility

AECOM AECOM Technical Services, Inc.

Aerostar Aerostar SES LLC

AFB Air Force Base

AFCEC Air Force Civil Engineering Center

AFFF aqueous film-forming foam

AOI Area of Interest

ARFF Aircraft Rescue and Firefighting

ARNG Army National Guard

ASE Aviation Support Equipment

ASTM American Society for Testing and Materials

bgs below ground surface

BRAC Base Realignment and Closure

CAARNG California Army National Guard

CAL FIRE California Department of Forestry and Fire Protection

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

CoC chain of custody

CSM conceptual site model

DA Department of the Army

DoD Department of Defense

DOT Department of Transportation

DQO data quality objective

DUA data usability assessment

DTSC Department of Toxic Substances Control, California

ELAP Environmental Laboratory Accreditation Program

EM Engineer Manual

FedEx Federal Express

FTA Fire Training Area

GPRS Ground Penetrating Radar Systems

HDPE high-density polyethylene 

HFPO-DA hexafluoropropylene oxide dimer acid

IDW investigation-derived waste

ITRC Interstate Technology Regulatory Council

LC/MS/MS liquid chromatography with tandem mass spectrometry

MGD million gallons per day

MIL-SPEC military specification

MS matrix spike

MSD matrix spike duplicate

NELAP National Environmental Laboratory Accreditation Program
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ng/L nanograms per liter

OSD Office of the Secretary of Defense

PA Preliminary Assessment

PFAS per- and polyfluoroalkyl substances

PFBS perfluorobutanesulfonic acid

PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acid

PFOA perfluorooctanoic acid

PFOS perfluorooctanesulfonic acid

PID photoionization detector

PQAPP Programmatic UFP-QAPP

PVC polyvinyl chloride

QA quality assurance 

QAPP Quality Assurance Project Plan

QC quality control

QSM Quality Systems Manual

RI Remedial Investigation

SI Site Inspection

SL screening level

SOP standard operating procedure

TOC total organic carbon

TPP Technical Project Planning

UFP Uniform Federal Policy

US United States

USACE United States Army Corps of Engineers

USCS Unified Soil Classification System

USEPA United States Environmental Protection Agency

USFWS United States Fish and Wildlife Service
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Executive Summary

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

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

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

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

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

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

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

, and perfluorobutanesulfonic acid 

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

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

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

used, stored, disposed, or released historically (see Table ES-2 for AOI locations). Additionally,

during development of the SI Quality Assurance Project Plan (QAPP) Addendum, based on 

discussion between ARNG and Department of the Air Force, additional joint fire training areas 

(FTAs) were identified as potential release areas at locations adjacent to the facility. These FTAs 

were identified as three additional AOIs. The objective of the SI is to identify whether there has 

been a release to the environment from the AOIs identified in the PA and during the SI planning

and determine whether further investigation is warranted, a removal action is required to address 

immediate threats, or no further action is required based on SLs for relevant compounds. This SI 

was completed at the Mather Army Aviation Support Facility (AASF) in Sacramento, California

and determined further evaluation under the Comprehensive Environmental Response, 

Compensation, and Liability Act (CERCLA) is warranted for each of the five AOIs. The Mather 

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

Mather AASF is located about 11 miles east of Sacramento and occupies 31 acres of land. The 

facility is an operational maintenance shop for California ARNG aircraft. The facility borders the 

Sacramento Mather Airport to the northeast and is situated in the Sacramento metropolitan area 

and Sacramento Valley.

The PA and SI QAPP Addendum identified five AOIs for investigation during the SI phase. SI 

sampling results from the five AOIs were compared to OSD SLs. Table ES-2 summarizes the SI 

results for each AOI. Based on the results of this SI, further evaluation under CERCLA is 

warranted in a Remedial Investigation (RI) for each of the five AOIs.

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

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

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

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

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

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

Analyteb

Residential

(Soil)

(μg/kg)a 

0-2 feet bgs

Industrial/ Commercial 

Composite Worker

(Soil)

(μg/kg)a 

2-15 feet bgs

Tap Water

(Groundwater)

(ng/L)a

PFOA 19 250 6

PFOS 13 160 4 

PFBS 1,900 25,000 601 

PFHxS 130 1,600 39

PFNA 19 250 6

Notes:

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

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

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

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

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

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

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

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

AOI

Potential 

Release 

Area

Soil – 

Source Area

Groundwater – 

Source Area

Groundwater –

Facility 

Boundary

Future Action

1 Wash Rack Proceed to RI

2

Airfields and 

AFFF 

Storage 

Areas

Proceed to RI

3

ARNG and 

Air Force 

FTA #1

N/A Proceed to RI

4 

ARNG and 

Air Force 

FTA #2

N/A Proceed to RI

5 

ARNG and 

Air Force 

FTA #3

N/A Proceed to RI

Legend:

N/A = not applicable

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected
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1. Introduction

1.1 Project Authorization

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

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

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

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

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

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

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

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

, and perfluorobutanesulfonic 

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

Aviation Support Facility (AASF) in Sacramento, California. The Mather AASF is also referred to 

as the “facility” throughout this document.

The SI project elements were performed in compliance with Comprehensive Environmental 

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

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

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

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

investigations.

1.2 SI Purpose

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

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

stored, disposed, or released historically. Furthermore, during development of the SI Quality 

Assurance Project Plan (QAPP) Addendum, based on discussion between ARNG and 

Department of the Air Force, additional joint fire training areas (FTAs) were identified as potential 

release areas at locations adjacent to the facility. These FTAs were identified as three additional 

AOIs. The objective of the SI is to identify whether there has been a release to the environment 

from these AOIs and determine whether further investigation is warranted, a removal action is 

required to address immediate threats, or no further action is required based on screening levels 

(SLs) for the relevant compounds. 

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

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

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

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

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

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

2.1 Facility Location and Description

Mather AASF is an operational maintenance shop for California ARNG (CAARNG) aircraft. The 

facility is in Mather Field, which is the former flightline operations area of Mather Air Force Base 

(AFB) and was granted for use and occupation by CAARNG under a 25-year land license 

beginning on 1 November 1985. Mather AFB was designated for realignment under the Base 

Realignment and Closure (BRAC) Commission in 1988, and closure occurred in 1993 (Amec 

Foster Wheeler, 2015). Following closure, the AASF was officially transferred from the 

Department of the Air Force to the DA, with the disclaimer that the Department of the Air Force 

would be responsible for the remediation of any environmental contamination caused by and 

resulting from Air Force activities. In 1994, the license for Mather AASF was amended to extend 

the licensing term indefinitely.

The facility borders the Sacramento Mather Airport to the northeast and is situated in the 

Sacramento metropolitan area and Sacramento Valley (Figure 2-1). The facility is about 11 miles 

east of downtown Sacramento as the distance from the nearest part of Sacramento city limits is 

only about 3 miles from the Mather AASF. 

2.2 Facility Environmental Setting

Mather AASF occupies 31 acres of land, approximately 97 percent (%) of which is composed of 

impervious surfaces (HazCon, 2017). The areas surrounding Mather AASF are primarily the cargo 

and general aviation facilities at the Sacramento Mather Airport. Other surrounding areas include 

the Mather Regional Park, Mather Commerce Center, a Veteran Affairs hospital complex, day 

care and elementary schools, churches, and residential communities to the north and south 

(Amec Foster Wheeler, 2015). The facility sits at an elevation of 92 feet above mean sea level, 

with a slight general topographic gradient to the west/southwest. There are no significant natural 

topographic features surrounding the facility (Figure 2-2). 

2.2.1 Geology

Mather AASF is located within the Great Valley geomorphic province, an alluvial plain located 

between the uplands of the Coast Ranges and the Sierra Nevada provinces (California Geological 

Survey, 2002). At the facility, Pleistocene-aged terrace sand, gravel, and cobbles overlie the

deeper Pliocene-aged Laguna Formation, which unconformably overlies the Early Pliocene 

Mehrten Formation (Amec Foster Wheeler, 2016; Marchand and Allwardt, 1981; Figure 2-3).

The uppermost geologic units at Mather AASF comprise three alluvial terrace deposits, which, 

from youngest to oldest, include the Riverbank, undifferentiated alluvial gravel, and Arroyo Seco 

formations (Shlemon et al., 2000). Mather AASF sits upon only the Riverbank terrace deposits; 

older terrace deposits are located south of the AASF. These deposits occur within nested fluvialfill terraces and ancient and active river channels and are each characterized by sand, gravel, 

and cobbles within silt and clay matrices of varying thickness and lateral extent. The Arroyo Seco 

Formation truncates the underlying Laguna Formation, which is a westward thickening alluvial 

wedge of interbedded clay and silt, sand, and gravel within a sandy to silty matrix (Marchand and 

Allwardt, 1981). The Laguna Formation directly overlies and is coeval to the Mehrten Formation, 

which comprises two interbedded units of gray to black sand and blue to brown clay, silt, and sand 

with some gravel. In the vicinity of Mather AASF, the Laguna Formation ranges from 200 to 400 

feet thick, and the Mehrten Formation ranges from 200 to 500 feet thick (Amec Foster Wheeler, 

2016).
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During the SI, well-graded gravel and low plasticity silts were observed as the dominant lithology 

of the unconsolidated sediments below the Mather AASF. The borings were completed at depths 

between 115 and 135 feet below ground surface (bgs). Isolated layers of silty sand were also 

observed in the borings with thicknesses ranging from approximately 2 to 15 feet. Since layers of 

clay were observed at location MAT-MW007, a sample for grain size analysis was collected and 

analyzed via American Society for Testing and Materials (ASTM) Method D-422. The results 

indicate that the soil sample is comprised primarily of silt (59.07%) and clay (23.25%). Boring logs 

are presented in Appendix E and grain size results are presented in Appendix F. 

2.2.2 Hydrogeology

The following hydrogeologic units were identified through previous investigations at Mather AFB 

(Aerostar, 2020b):

• Unit Ap (upper unit of the Laguna Formation)

• Unit A (upper unit of the Laguna Formation)

• Unit Bu (middle unit of Laguna Formation)

• Unit B (middle unit of the Laguna Formation)

• Unit C (lower unit of the Laguna Formation)

• Unit D (lower unit of the Laguna Formation)

• Mehrten Formation (Laguna-Mehrten Transition (LMT) Zone)

Unit Ap contains a perched water-bearing zone, and Unit B generally has the highest potential for 

contaminant migration due to a high transmissivity. Units A through C are transected by the water 

table going from east to west across the former Mather AFB (Amec Foster Wheeler, 2016). Two 

primary aquifers exist within the unconsolidated deposits of the Laguna and Mehrten Formations. 

The majority of potable wells are screened within hydrostratigraphic Units B, D and the LTM Zone

Aerostar, 2020b).

Regional groundwater flow is generally in the southwest direction but may be influenced by 

groundwater pumping for potable use, agriculture, and industrial uses. Localized groundwater

flow is also generally in the southwest direction, with an average hydraulic gradient of 0.002 feet 

per feet (Amec Foster Wheeler, 2015). However, a large potentiometric depression had formed 

along the northwestern installation boundary of former Mather AFB due to remedial pumping in 

extraction wells; therefore, local groundwater variations are expected (URS Group, Inc., 2014). 

Depth to groundwater was measured at approximately 40 feet bgs for the perched aquifer and 90 

feet bgs for the deeper aquifer, both of which lie within the Laguna Formation (Amec Foster 

Wheeler, 2015). However, the perched aquifer did not appear to be present beneath the AASF. 

Groundwater features are presented on Figure 2-3. 

Mather AASF is located in the Sacramento County Water Agency’s Zone 40 North Service Area, 

which receives potable water from the existing water distribution system at former Mather AFB. 

The Mather AFB water distribution system was conveyed in 1998 via an easement to Sacramento 

County. Currently, the water distribution system includes two groundwater wells and a six million 

gallons per day (MGD) water treatment plant located at the Independence of Mather residential 

development (US Army Corps of Engineers [USACE], 2012). However, potable water was 

additionally derived from wells located in the weapons storage area/K-9 compound prior to Mather 

AFB closure and from four main base wells prior to 1997 (Amec Foster Wheeler, 2015).
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In 2022, the County water system pulled water from four of their five wells and usually used more 

than two at any given time. One well in that system was not used by the County because it was 

too close to a sewer line, but was used by the AF. Depths to water measured in April 2022 during 

the SI ranged from 93.06 to 96.97 feet bgs. Groundwater elevation contours from the SI are 

presented on Figure 2-4 and indicate the localized groundwater flow direction at the AASF is 

primarily to the southwest. 

2.2.3 Hydrology 

A drainage ditch located near the northeastern portion of the AASF flows south beneath the 

runways to the South Ditch and then to Morrison Creek that eventually flows to the Sacramento 

River. Storm water in the northeastern airfield and refueling pads is drained in the northeast 

direction, towards the drainage ditch. All other storm water is diverted to storm drain inlets on and 

around the AASF that connect to the drainage system of Mather Field (HazCon, 2017). There are 

no identified wetlands within the AASF property, but several seasonal wetlands exist in 

undeveloped portions of Mather Field due to the presence of an underlying impermeable soil layer 

of clay or hardpan (Amec Foster Wheeler, 2015).

Surface water runoff generally follows the slope of the American River valley and drains westsouthwest. While large-scale watershed maps show most of Mather AASF in the Lake 

Greenhaven-Sacramento River Watershed, constructed drainage systems direct water from the 

facility into the Upper Morrison Creek Watershed. Morrison Creek is located approximately 1.5 

miles to the southeast and is a tributary of the Sacramento River, located approximately 12 miles 

west of Mather AASF. Surface water in the drainage system of Mather Field is also captured in 

various drainage ditches such as the West Ditch and South Ditch. Surface water features are 

presented on Figure 2-5. 

2.2.4 Climate 

Mather AASF is in a semi-arid, Mediterranean climate zone. The winter “rainy season” extends 

from November to February, and the summer “dry season” extends from June to August. The 

average annual rainfall is approximately 20 inches. Summer temperatures peak in July, with an 

average high of 94 degrees Fahrenheit (°F) and an average low of 61 °F. Winter temperatures 

are lowest in December, with an average high of 55 °F and an average low of 40 °F. Prevailing 

wind speeds are southerly year-round due to the orientation of the Sacramento Valley and 

influence of the Sierra Nevada Mountains. Snowfall is extremely rare, but frost occasionally 

occurs (Cline, Neigher, and Bellinder; 2010).

2.2.5 Current and Future Land Use

Mather AASF serves as a CAARNG aviation maintenance and storage facility for rotary and fixedwing aircraft. Mather AASF is comprised of a hangar, maintenance and storage areas, operations 

and administrative buildings, and related infrastructure including parking lots, aircraft parking 

areas, wash rack, and refueling pads, and is categorized as a small-quantity hazardous waste 

generator. The facility is fenced with secured access. Reasonably anticipated future land use is 

not expected to change from the current land use described above.

2.2.6 Sensitive Habitat and Threatened/ Endangered Species

The following amphibians, birds, crustaceans, fishes, plants, insects, mammals, and reptiles are 

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

Sacramento County, California (US Fish and Wildlife Service [USFWS], 2022). While identified in 

the county, these species may not be present at the facility.
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• Amphibians: California tiger Salamander, Ambystoma californiense (threatened);

California red-legged frog, Rana draytonii (threatened);

• Birds: Yellow-billed Cuckoo, Coccyzus americanus (threatened); Least Bell's vireo, Vireo

bellii pusillus (endangered); California clapper rail, Rallus longirostris obsoletus

(endangered); Western snowy plover, Charadrius nivosus nivosus (threatened); California

least tern, Sterna antillarum browni (endangered);

• Crustaceans: Vernal pool fairy shrimp, Branchinecta lynchi (threatened); Conservancy fairy

shrimp, Branchinecta conservation (endangered); Vernal pool tadpole shrimp, Lepidurus

packardi (endangered);

• Fishes: Delta smelt, Hypomesus transpacificus (threatened); longfin smelt, Spirinchus

thaleichthys (candidate);

• Flowering Plants: Sacramento Orcutt grass, Orcuttia viscida (endangered); Ione

manzanita, Arctostaphylos myrtifolia (threatened); Palmate-bracted bird's beak,

Cordylanthus palmatus (endangered); Fleshy owl's-clover, Castilleja campestris ssp.

succulenta (threatened); Slender Orcutt grass, Orcuttia tenuis (threatened); Colusa grass,

Neostapfia colusana (threatened); El Dorado bedstraw, Galium californicum ssp. sierrae

(endangered); Pine Hill ceanothus, Ceanothus roderickii (endangered); Layne's butterweed,

Senecio layneae (threatened); Stebbins' morning-glory, Calystegia stebbinsii (endangered);

Soft bird's-beak, Cordylanthus mollis ssp. mollis (endangered); Ione (incl. Irish Hill)

buckwheat; Eriogonum apricum (incl. var. prostratum) (endangered); Pine Hill flannelbush,

Fremontodendron californicum ssp. decumbens (endangered);

• Insects: Monarch butterfly, Danaus plexippus (candidate); Valley elderberry longhorn

beetle, Desmocerus californicus dimorphus (threatened);

• Mammals: Riparian brush rabbit, Sylvilagus bachmani riparius (endangered);

• Reptiles: Giant garter snake, Thamnophis gigas (threatened).

2.3 History of PFAS Use

Four potential release areas were identified at Mather AASF during the PA where AFFF may have 

been used or released historically (AECOM, 2020). AFFF may have historically been released at 

the facility during familiarization training exercises, fire training activities, and AFFF storage may 

have occurred as early as 1998. During development of the SI QAPP Addendum, three adjacent, 

off-facility FTAs were identified where combined ARNG and Air Force fire training activities 

occurred from as early as 1998 until approximately 2003 (AECOM 2020). Training by the Air Force 

did not continue beyond closure of Mather AFB in 1993. The seven potential release areas were 

grouped into five AOIs based on proximity to one another and presumed groundwater flow. A 

description of each AOI is presented in Section 3. 
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AECOM 3-1

3. Summary of Areas of Interest

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

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

identified at Mather AASF and grouped into two AOIs (AECOM, 2020). Additionally, during

development of the SI QAPP Addendum (AECOM, 2021), three adjacent, off-facility joint 

ARNG/Air Force FTAs were identified and grouped into three additional AOIs. A resulting total of 

five AOIs were investigated during the SI. The potential release areas are shown on Figure 3-1. 

3.1 AOI 1 Wash Rack

AOI 1 is the wash rack, where one instance of a fire training exercise occurred in approximately 

2010 and may have resulted in a potential AFFF release. The fire training event involved the 

discharge of Tri-MaxTM fire extinguishers of which the exact contents are unknown.

The drains in the wash rack area lead to an oil water separator and then flow into the sanitary 

sewer system. Therefore, potential discharges of AFFF in the wash rack would primarily release 

directly into the sanitary sewer system. The sanitary sewer system is serviced by the Sacramento 

Regional County Sanitation District and Sacramento Area Sewer District. Wastewater is conveyed 

to the Sacramento Regional Wastewater Treatment Plant, which provides secondary wastewater 

treatment, participates in biosolids recycling/ land disposal, and discharges approximately 150 

MGD into the Sacramento River, located about 14 miles southwest of the AASF (USACE, 2012). 

However, any runoff not captured by the oil water separator could reach nearby surface drainages 

that lead into tributaries of the Sacramento River.

3.2 AOI 2 Airfields and AFFF Storage Areas

AOI 2 is comprised of the three AASF airfields: the Aviation Support Equipment (ASE) Storage 

Building, the C-12 Hangar, and the Storage Shed. Familiarization training exercises with TriMaxTM fire extinguishers took place at the three AASF airfields (Northeast Airfield, Center Airfield, 

and Southwest Airfield) and occurred approximately annually during the confirmed years of 1998 

to 2003. The ASE Storage Building and C-12 Hangar contained storage of decommissioned TriMaxTM fire extinguishers, and the Storage Shed contained storage of AFFF in 5-gallon containers.

3.3 AOI 3 ARNG and Air Force FTA #1

AOI 3 is the first of three adjacent, off-facility FTAs identified where combined ARNG and Air Force 

extraction type exercises may have involved extinguishing live fire with either water or an 

unknown type of foam. The FTA exercises took place as early as 1988 until approximately2003

(AECOM 2020). Training by the Air Force did not continue beyond closure of Mather AFB in 1993.

3.4 AOI 4 ARNG and Air Force FTA #2

AOI 4 is the second of three adjacent, off-facility FTAs identified where combined ARNG and Air 

Force extraction type exercises may have involved extinguishing live fire with either water or an 

unknown type of foam. The FTA exercises took place as early as 1988 until approximately 2003

(AECOM 2020). Training by the Air Force did not continue beyond closure of Mather AFB in 1993.

3.5 AOI 5 ARNG and Air Force FTA #3

AOI 5 is the third of three adjacent, off-facility FTAs identified where combined ARNG and Air 

Force extraction type exercises may have involved extinguishing live fire with either water or an 
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AECOM 3-2

unknown type of foam. The FTA exercises took place as early as 1988 until approximately 2003

(AECOM 2020). Training by the Air Force did not continue beyond closure of Mather AFB in 1993.

3.6 Adjacent Sources

Numerous off-facility, potential sources were identified adjacent to the Mather AASF during the 

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

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

investigated as part of this SI. 

3.6.1 Former Mather Air Force Base 

Former Mather AFB was located on an approximately 5,845-acre property. Mather AFB began 

operations in 1918 and was designated for realignment under BRAC in 1988. Closure occurred 

in 1993 and the installation transitioned to civilian use (Amec Foster Wheeler, 2015).

Operations related to the use and/or storage of AFFF have historically occurred at various 

locations at former Mather AFB. A 2015 PA report on PFAS identified 10 potential PFAS release 

locations (Amec Foster Wheeler, 2015). One area, the former Mather AFB FTA site FT011P, was 

investigate during a 2016 SI report that confirmed that PFOS concentrations in soil exceeded 

USAF-calculated screening values derived from the the Office of Superfund Remediation and 

Technology Innovation (OSRTI) residential direct contact soil criteria (5 milligrams per kilogram 

[mg/kg] for PFOS and 12 mg/kg for PFOA in soil and sediment), and PFOS and PFOA 

concentrations in groundwater exceeded the Health Advisories (Amec Foster Wheeler, 2016). 

The former Mather AFB PFAS investigation reports are included in the PA (AECOM, 2020). Three

areas were categorized as no further action (Mather AFB West Ditch, Mather AFB South Ditch 

and Mather AFB Main Runway [Figure 3-1]), and the remaining seven areas were investigated in 

a later SI between December 2016 and July 2018 (Aerostar SES LLC [Aerostar], 2020a). The 

relevant compounds were detected in groundwater with the following maximum concentrations: 

PFOA at 3,130 nanograms per liter (ng/L); PFOS at 26,000 ng/L; PFHxS at 31,200 ng/L; PFNA 

at 16.5 ng/L; and PFBS at 1,270 ng/L (Aerostar, 2020a). The relevant compounds were detected 

in soil with the following maximum concentrations: PFOA at 58.1 micrograms per kilogram (μg/kg); 

PFOS at 1,780 J μg/kg; PFHxS at 126 μg/kg; PFNA at 7.37 μg/kg; and PFBS at 41.7 μg/kg 

(Aerostar, 2020a).

An expanded SI was completed in 2020 to further determine the presence or absence of PFOA 

and PFOS in the drinking water aquifer (Aerostar, 2020b). Summary information below can be 

found in Figure 4-4 of Aerostar, 2020b. Data included in this figure was collected over the span of 

2014 through 2020. A PFOA/PFOS plume, associated with the Main Base Strategic Air Command 

Area groundwater treatment plant, was documented cross-gradient, less than 0.5-miles west of 

Mather AASF, in hydrogeologic Unit D (Figure 4-4, Aerostar, 2020b). Within the plume, PFOA and 

PFOS were detected at concentrations up to 99 ng/L and 255 ng/L, respectively. A second 

comingled PFOA/PFOS plume, associated with six potential release areas, was identified less 

than 1-mile downgradient of Mather AASF, in hydrogeologic Units B and C (Figure 4-4, Aerostar, 

2020b). These six release areas are divided into two source areas: a northern source area 

containing AFFF Areas 3, 4, and 5 and a southern source area containing AFFF Area 10, FT011, 

and Site 7. Within the southern source area, groundwater samples were collected from 

hydrogeologic Unit A (32.5 – 67 feet bgs). From this source area, PFOA and PFOS were detected 

at concentrations up to 19,000 ng/L and 891,000 ng/L, respectively. Within the associated 

downgradient plume in hydrogeologic Units B and C, PFOA and PFOS were detected at 

concentrations up to 549 ng/L and 1,020 ng/L, respectively (Figure 4-4, Aerostar, 2020b). Limited 

data were available upgradient of Mather AASF. In July 2020, PFOA and PFOS were detected at 

concentrations of 2.4 J ng/L and 1.5 J ng/L, respectively, in well STSW-175A (screened at 275-

295 feet bgs), located less than 1-mile upgradient of Mather AASF. During the same event, PFOA 
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AECOM 3-3

was also detected directly north of Mather AASF, at a concentration of 14.3 ng/L in well STSW105C (screened at 380-400 feet bgs).

Additionally, quarterly monitoring events have been conducted under the former Mather AFB 

groundwater remediation and monitoring program. During the third quarter of 2022, a selection of 

18 locations were sampled and analyzed for PFAS. Results indicated the presence of the relevant 

compounds with the following maximum concentrations: PFOA at 75 ng/L; PFOS at 23 ng/L; 

PFHxS at 32 ng/L; PFNA at 2 ng/L; and PFBS at 8 ng/L (Air Force Civil Engineering Center 

[AFCEC], 2022).

3.6.2 Elite Air Interiors

Elite Air Interiors is a private aviation company present at Sacramento Mather Airport. The 

company provides interior refurbishment services for aviation aircrafts. The company’s website 

advertises using “the highest quality, fire retardant, HR upholstery foams”. PFAS contamination 

from these industrial applications is unknown but possible (Elite Air Interiors, n.d.). The Elite Air 

Interiors hangar was previously a Mather AFB maintenance hangar (Building 7015) that stored 

AFFF and contained an AFFF fire suppression system. The Mather AFB maintenance hangar was 

identified as a potential PFAS release area in the former Mather AFB PA report (Amec Foster 

Wheeler, 2016).

3.6.3 Fire Training Area

During an interview with Mather AASF personnel, the area located northeast of the Sacramento 

Mather Airport was identified as an FTA. The FTA’s geographic coordinates are 38°34’08.5”N; 

121°15’47.6”W, and the area is not within the boundary of the former Mather AFB. The parcel 

number is 072-2860-003-0000, is owned by Sacramento Metropolitan Fire District. and a Federal 

Express (FedEx) airplane is apparently parked in the area at all times. The property was last 

transferred on 5 October 2007 No further details, such as AFFF usage or fire training activities, 

are known about the FTA.

3.6.4 California Department of Forestry and Fire Protection 

The California Department of Forestry and Fire Protection (CAL FIRE) maintains a hangar located 

adjacent to Elite Air Interiors. The CAL FIRE hangar was previously a Mather AFB maintenance 

hangar (Building 7040) that stored AFFF and contained an AFFF fire suppression system. The 

Mather AFB maintenance hangar was identified as a potential PFAS release area in the former 

Mather AFB PA report (Amec Foster Wheeler, 2016).

3.6.5 Mather Aircraft Rescue and Firefighting 

Mather Aircraft Rescue and Firefighting (ARFF) has a fire station on Sacramento Mather Airport 

property that provides emergency response to aircraft emergencies. According to an interview 

with two Mather ARFF firefighters, Mather ARFF has occupied the fire station since 2000, after 

the Emery Worldwide Flight 17 crash incident prompted the need for a municipal fire and 

emergency response unit at Sacramento Mather Airport. The ARFF stores AFFF in their firetrucks, 

although they do not currently conduct fire training with AFFF at the station and are in the midst 

of transitioning out of AFFF usage. However, the ARFF firefighters indicated that they participated 

in a helicopter crash fire training exercise at the airport airfield in approximately 2011. The exact 

location and what the fire training exercise entailed, such as if AFFF were used, was not specified.

The fire station was previously occupied by the Mather AFB firefighting unit, who stored their crash 

response trucks in the station. The fire station (Building 7075) was also identified as a potential 

PFAS release area in the former Mather AFB PA report (Amec Foster Wheeler, 2016).
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AECOM 3-4

3.6.6 Emery Worldwide Flight 17 Crash 

On 16 February 2000, Emery Worldwide Airlines, Inc. (Emery Worldwide) Flight 17 crashed into 

an auto salvage yard, approximately 2.5 miles east of the Sacramento Mather Airport. The 

airplane was attempting to return to the airport after experiencing a loss of pitch control (National 

Transportation Safety Board, 2003). The auto salvage yard contained 573 cars, some of which 

were set ablaze by the crash. According to eyewitness accounts, jet fuel was spilled on the ground 

and “flames went up about 200 to 300 feet in the air” (Curiel et al., 2000). Due to the presence of 

a fuel fire, firefighting response with foam is likely, although the type of foam (Class A or AFFF) 

and quantity used are unknown.

3.6.7 Air Force B-52 Bomber Crash 

On December 1982, an Air Force B-52 bomber plane crashed into a cow pasture while practicing 

simulated combat takeoff exercises. The crash location was approximately one mile west of the 

Mather AFB runway and nearby a busy intersection (McKinley, 1982). Due to the historical usage 

of AFFF by former Mather AFB, it is possible that AFFF may have been used in the emergency 

response.
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AECOM 4-1

4. Project Data Quality Objectives

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

Addendum (AECOM, 2021), the objective of the SI is to identify whether there has been a release 

to the environment at the AOIs. For each AOI, ARNG determines if further investigation is 

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

is warranted. This SI evaluated groundwater and soil for presence or absence of relevant 

compounds at each of the sampled AOIs.

4.1 Problem Statement

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

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

SLs are presented in Section 6.1 of this report.

4.2 Information Inputs

Primary information inputs included:

• The PA for Mather AASF (AECOM, 2020);

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

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

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

parameters measured at the time of sampling.

4.3 Study Boundaries

The scope of the SI was the property limits of the facility with the addition of three nearby AOIs outside 

the facility boundaries. (Figure 2-2). Off-facility sampling was not included in the scope of this SI. If 

future off-facility sampling is required, the proper stakeholders will be notified, and necessary rights of 

entry will be obtained by ARNG with property owner(s). Temporal boundaries were limited to the spring

season, which was the earliest available time field resources were available to complete the study.

4.4 Analytical Approach

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

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

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

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

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

4.5 Data Usability Assessment

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

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

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

methods, the assessment determines whether project execution and the resulting data have met 

installation-specific DQOs. Both sampling and analytical activities are considered to assess 

whether the collected data are of the right type, quality, and quantity to support the decisionmaking (DoD, 2019a; DoD, 2019b; USEPA, 2017). 
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AECOM 4-2

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

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

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

requirements of the SI QAPP Addendum (AECOM, 2021).
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AECOM 5-1

5. Site Inspection Activities

This section describes the environmental investigation and sampling activities that occurred as 

part of the SI. The SI sampling approach was based on the findings of the PA and implemented 

in accordance with the following approved documents: 

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

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

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

• Final Preliminary Assessment Report, Mather AASF, California dated February 2020

(AECOM, 2020);

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

Mather Army Aviation Support Facility, Sacramento, California dated November 2021

(AECOM, 2021); and

• Final Site Safety and Health Plan, Mather Army Aviation Support Facility, Sacramento,

California dated March 2022 (AECOM, 2022).

The SI field activities were conducted from 28 March 2022 to 16 April 2022 and consisted of utility 

clearance, hand augering, sonic boring, soil sample collection, permanent monitoring well 

installation, groundwater sample collection, and land surveying. Field activities were conducted in 

accordance with the SI QAPP Addendum (AECOM, 2021), except as noted in Section 5.8. 

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

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

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

• Twenty-three (23) soil samples from seven boring locations and two hand auger locations;

• Eight groundwater samples from eight permanent monitoring wells;

• Eighteen (18) quality assurance (QA)/quality control (QC) samples.

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

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

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

in Appendix B1. Sampling forms and well development forms are provided in Appendix B2. A 

Field Change Request Form is provided in Appendix B3. A Nonconformance and Corrective 

Action Report is provided in Appendix B4, and land survey data are provided in Appendix B5. 

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

5.1 Pre-Investigation Activities

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

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

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

5.1.1 Technical Project Planning

The USACE TPP Process, Engineer Manual (EM) 200-1-2 (USACE, 2016) defines four phases 

to project planning: 1.) defining the project phase; 2.) determining data needs; 3.) developing data 

collection strategies; and 4.) finalizing the data collection plan. The process encourages 
Site Inspection Report

Mather Army Aviation Support Facility, Sacramento, California

AECOM 5-2

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 6 April 2021, prior to SI field activities. The 

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

stakeholders for this SI include the ARNG, CAARNG, USACE, California Regional Water Quality 

Control Board, California Department of Toxic Substances Control (DTSC), US Air Force BRAC, 

and USEPA Region 9. Stakeholders were provided the opportunity to make comments on the 

technical sampling approach and methods at the combined TPP Meeting 1 and 2. The outcome 

of the combined TPP Meeting 1 and 2 was memorialized in the SI QAPP Addendum (AECOM, 

2021).

A TPP Meeting 3 was held on 12 July 2023 to discuss the results of the SI. Meeting minutes for 

TPP 3 are included in Appendix D of this report. 

5.1.2 Utility Clearance 

AECOM placed a ticket with the USA north 811 “Call Before You Dig” California utility clearance 

provider to notify them of intrusive work on 21 March 2022. Additionally, AECOM contracted

Ground Penetrating Radar Systems (GPRS), a private utility location service, to perform utility 

clearance. GPRS performed utility clearance of the proposed boring locations on 28 March 2022

with input from the AECOM field team and Mather AASF facility staff. General locating services 

and ground-penetrating radar were used to complete the clearance. Additionally, the first five feet 

of each boring were pre-cleared using a hand auger to verify utility clearance in shallow 

subsurface where utilities would typically be encountered. 

5.1.3 Source Water and Sampling Equipment Acceptability

A potable water source at Mather AASF was sampled on 15 October 2021 to assess usability for 

decontamination of drilling equipment. Results of the sample collected at the wash rack spigot 

(MAT-DECON-01) confirmed this source to be acceptable for use in this investigation; therefore, 

it was used throughout the field activities. Specifically, the samples were analyzed by LC/MS/MS 

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

with the wash rack spigot source used during the SI are provided in Appendix F. A discussion of 

the results is presented in the DUA (Appendix A).

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

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

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

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

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

regarding the allowable materials within the sampling environment. 

5.2 Soil Borings and Soil Sampling

Soil samples were collected via hand auger and Sonic drilling methods, in accordance with the SI 

QAPP Addendum (AECOM, 2021). Hand augers were used at locations designated for collection 

of surface soil samples (0 to 2 feet bgs). A Fraste Eijkelkamp FS250 rotosonic drill rig was used 

to collect continuous soil cores to the target depth at each boring location; however, a hand auger 

was used to collect soil from the top five feet of the boring, in accordance with AECOM utility 

clearance procedures. The soil boring locations are shown on Figure 5-1, and depths are 

provided Table 5-2. 
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Mather Army Aviation Support Facility, Sacramento, California

AECOM 5-3

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

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

13 to 15 feet bgs, and one subsurface soil sample approximately 2 feet above the groundwater 

table. At boring MAT-MW007, asphalt was observed to be approximately 2 feet thick, so the 0 to 

2 feet bgs surface soil sample was collected at the soil interface at 2 feet bgs.

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

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

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

Observations and measurements were recorded on boring logs (Appendix B2) and in a nontreated field logbook (i.e., composition notebook). Depth interval, recovery thickness, PID 

concentrations, moisture, relative density, color (using a Munsell soil color chart), and texture 

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

Soil borings completed during the SI found well-graded gravel and low plasticity silts as the 

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

completed at depths between 115 and 135 feet bgs. Isolated layers of silty sand were also 

observed in the boring logs at thicknesses ranging from approximately 2 to 15 feet. 

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

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

and transported via FedEx under standard chain of custody (CoC) procedures to the laboratory 

and analyzed by LC/MS/MS compliant with QSM 5.3 Table B-15, total organic carbon (TOC) 

(USEPA Method 9060A), pH (USEPA Method 9045D), and grain size (ASTM Method D-422) in 

accordance with the SI QAPP Addendum (AECOM, 2021).

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

as the accompanying samples. Matrix spike (MS)/MS duplicates (MSDs) were collected at a rate 

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

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

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

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

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

Once the sonic boreholes had been advanced to the specified depth, a permanent monitoring 

well was installed in accordance with the SI QAPP Addendum (AECOM, 2021). Surface soil-only 

boring locations AOI01-01 and AOI01-02, collected via hand auger, were abandoned using 

hydrated bentonite chips.

5.3 Permanent Well Installation and Groundwater Sampling

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

source areas. The locations of the wells are shown on Figure 5-1. 

A Fraste Eijkelkamp FS250 rotosonic drill rig was used to install seven 2-inch diameter monitoring 

wells. The monitoring wells were constructed with Schedule 40 polyvinyl chloride (PVC), flush 

threaded 10-foot sections of riser, 0.010-inch slotted well screen, and a sand trap bottom. A filter 

pack of 2/12 Monterrey sand was installed in the annulus around the well screen and placed at 

least 2 feet above the top of the well screen. A minimum of a 2-foot-thick bentonite seal was 

placed above the filter sand and hydrated. Bentonite grout was placed in the well annulus from 

the top of the bentonite seal to approximately 2 feet bgs for the completion of a flush-mount well 

vault. The bentonite grout was allowed to set for 24 hours prior to well completion in accordance 

with the SI QAPP Addendum (AECOM, 2021). The screen interval of each groundwater

monitoring well is provided in Table 5-3, and construction details are provided in Appendix E. 
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Mather Army Aviation Support Facility, Sacramento, California

AECOM 5-4

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

(AECOM, 2021). The newly installed monitoring wells were developed no sooner than 24 hours 

following installation by pumping and surging using a variable speed submersible pump. Samples 

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

using a Geotech bladder pump with disposable PFAS-free, HDPE tubing. New tubing was used 

at each well and the pumps were decontaminated between each well. The wells were purged at 

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

(e.g., temperature, specific conductance, pH, dissolved oxygen, and oxidation-reduction 

potential) were measured using a water quality meter and recorded on the field sampling form 

(Appendix B2). Water levels were measured to the nearest 0.01 inch and recorded. Additionally, 

a subsample of each groundwater sample was collected in a separate container, and a shaker 

test was completed to identify if there were any foaming. No foaming was noted in any of the 

groundwater samples.

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

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

standard CoC procedures to the laboratory and analyzed by LC/MS/MS compliant with QSM 5.3

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

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

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

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

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

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

5.4 Synoptic Water Level Measurements

A synoptic groundwater gauging event was performed on 15 April 2022. Groundwater elevation 

measurements were collected from the seven new permanent monitoring wells and two existing 

monitoring wells. Water level measurements were taken from the northern side of the well casing. 

A groundwater flow contour map is provided in Figure 2-4. Groundwater elevation data are

provided in Table 5-3.

5.5 Surveying

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

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

Survey data from the newly installed wells on the facility were collected on 14 April 2022 in the 

applicable Universal Transverse Mercator zone projection with North American Datum 1983 

(NAD83) datum (horizontal) and North American Vertical Datum 1988 (vertical). The surveyed 

well data are provided in Appendix B5.

5.6 Investigation-Derived Waste

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

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

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

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

Soil IDW (i.e., soil cuttings) generated during the SI activities were contained in labeled, 55-gallon 

Department of Transportation (DOT)-approved steel drums and left onsite in a designated waste 

storage area. The soil IDW was not sampled and assumes the characteristics of the associated 

soil samples collected from that source location. ARNG will coordinate waste profiling, 

transportation, and disposal of the solid IDW under a separate contract.
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Mather Army Aviation Support Facility, Sacramento, California

AECOM 5-5

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

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

Management and disposal of containerized IDW is being handled by EA Engineering, Science, 

and Technology, Inc. (EA) under a separate contract with USACE in accordance with SOP No. 

042A (EA, 2021)

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

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

activities were disposed of at a licensed solid waste landfill.

5.7 Laboratory Analytical Methods

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

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

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

5.8 Deviations from SI QAPP Addendum

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

documentation as noted below:

• During installation of monitoring wells, 2-inch diameter Schedule 40 PVC was used instead

of 4-inch diameter Schedule 80 PVC as specified in the SI QAPP Addendum. The decision

was based on the driller’s recommendation and extensive experience at the drilling site. The

proposed change was in conformance with Sacramento County Environmental

Management Department well construction standards, and the revised design ensured

DQOs were achieved. This action was documented in a field change request form provided

in Appendix B3.

• Dedicated sampling equipment was observed in existing permanent well MAFB-096. Efforts

to remove the equipment were unsuccessful; therefore, a groundwater sample from existing

permanent well MAFB-096 could not be collected. This action was documented in a

nonconformance report dated 15 April 2022 and is provided in Appendix B4.

While not noted on the Log of Daily Notice, the pump for well MAFB-097 was reinstalled after 

sampling and before AECOM demobilized from the site.

AFCEC was involved during review of the field documentation, and the actions of these two 

deviations were coordinated with AFCEC.
Site Inspection Report

Mather Army Aviation Support Facility, Sacramento, California

AECOM 5-6

THIS PAGE INTENTIONALLY BLANK
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, Mather AASF, California

Sample Identification

Sample

Collection 

Date/Time

Sample Depth 

(feet bgs)

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

Comments

AOI01-01-SB-0-2 4/6/2022 9:10 0 - 2 x

AOI01-01-SB-0-2-D 4/6/2022 9:10 0 - 2 x FD

AOI01-02-SB-0-2 4/7/2022 8:15 0 - 2 x x x pH/TOC

AOI01-02-SB-0-2-MS 4/7/2022 8:15 0 - 2 x x MS

AOI01-02-SB-0-2-MSD 4/7/2022 8:15 0 - 2 x x MSD

MAT-MW001-SB-0-2 4/8/2022 8:30 0 - 2 x

MAT-MW001-SB-13-15 4/8/2022 8:45 13 - 15 x

MAT-MW001-SB-97-99 4/8/2022 16:15 97 - 99 x

MAT-MW002-SB-0-2 4/1/2022 12:50 0 - 2 x

MAT-MW002-SB-0-2-MS 4/1/2022 12:50 0 - 2 x MS

MAT-MW002-SB-0-2-MSD 4/1/2022 12:50 0 - 2 x MSD

MAT-MW002-SB-13-15 4/1/2022 13:45 13 - 15 x

MAT-MW002-SB-13-15-D 4/1/2022 13:45 13 - 15 x FD

MAT-MW002-SB-114-116 4/4/2022 12:05 114 - 116 x

MAT-MW003-SB-0-2 4/7/2022 10:30 0 - 2 x

MAT-MW003-SB-13-15 4/7/2022 10:50 13 - 15 x

MAT-MW003-SB-13-15-MS 4/7/2022 10:50 13 - 15 x MS

MAT-MW003-SB-13-15-MSD 4/7/2022 10:50 13 - 15 x MSD

MAT-MW003-SB-110-112 4/7/2022 15:30 110 - 112 x

MAT-MW004-SB-0-2 4/6/2022 11:20 0 - 2 x x x pH/TOC

MAT-MW004-SB-13-15 4/6/2022 11:45 13 - 15 x

MAT-MW004-SB-103-105 4/6/2022 17:20 103 - 105 x

MAT-MW005-SB-0-2 3/30/2022 16:20 0 - 2 x x x pH/TOC

MAT-MW005-SB-13-15 3/30/2022 17:15 13 - 15 x

MAT-MW005-SB-122-124 3/31/2022 13:10 122 - 124 x

MAT-MW005-SB-122-124-D 3/31/2022 13:10 122 - 124 x FD

MAT-MW006-SB-0-2 4/5/2022 8:20 0 - 2 x x x pH/TOC

MAT-MW006-SB-0-2-D 4/5/2022 8:20 0 - 2 x x x FD, pH/TOC

MAT-MW006-SB-13-15 4/5/2022 8:45 13 - 15 x

MAT-MW006-SB-101-103 4/5/2022 15:45 101 - 103 x

MAT-MW007-SB-0-2 3/29/2022 8:02 0 - 2 x x x pH/TOC

MAT-MW007-SB-13-15 3/29/2022 8:55 13 - 15 x

MAT-MW007-SB-95-100 3/30/2022 9:25 95 - 100 x Grain Size

MAT-MW007-SB-98-100 3/30/2022 10:00 98 - 100 x

MAT-MW001-GW 4/14/2022 17:13 NA x

MAT-MW001-GW-MS 4/14/2022 17:13 NA x MS

MAT-MW001-GW-MSD 4/14/2022 17:13 NA x MSD

MAT-MW002-GW 4/16/2022 11:23 NA x

MAT-MW003-GW 4/13/2022 12:50 NA x

MAT-MW004-GW 4/13/2022 10:05 NA x

MAT-MW005-GW 4/14/2022 14:58 NA x

MAT-MW006-GW 4/14/2022 12:05 NA x

MAT-MW006-GW-D 4/14/2022 12:05 NA x FD

MAT-MW007-GW 4/14/2022 9:33 NA x

MAFB-097-GW 4/16/2022 9:05 NA x

Soil Samples

Groundwater Samples

AECOM 5-7
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, Mather AASF, California

Sample Identification

Sample

Collection 

Date/Time

Sample Depth 

(feet bgs)

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

Comments

MAT-FRB-01 3/31/2022 7:35 NA x FRB

MAT-ERB-01 3/31/2022 7:30 NA x drill bit

MAT-ERB-02 4/7/2022 17:05 NA x hand auger

MAT-ERB-03 4/14/2022 1405 NA x bladder pump

MAT-DECON-01 10/15/2021 12:10 NA x wash rack spigot

Notes:

AASF = Army Aviation Support Facility

AOI = area of interest

ASTM = American Society for Testing and Materials

bgs = below ground surface

Decon = decontamination

ERB = equipment rinsate blank

FD = field duplicate

FRB = field reagent blank

GW = groundwater

LC/MS/MS = Liquid Chromatography Mass Spectrometry

MAFB = Mather Air Force Base

MAT = Mather

MS/MSD = matrix spike/ matrix spike duplicate

MW = monitoring well

QSM = Quality Systems Manual

SB = soil boring

TOC = total organic carbon

USEPA = United States Environmental Protection Agency

Quality Control Samples

AECOM 5-8
Table 5-2

Soil Boring Depths

Site Inspection Report, Mather AASF, California

Area of Interest

Boring 

Location

Soil Boring Depth 

(feet bgs)

1 MAT-MW003 122

MAT-MW001 115

MAT-MW002 127

MAT-MW004 115

3 MAT-MW005 135

4 MAT-MW006 115

5 MAT-MW007 115

Notes:

AASF = Army Aviation Support Facility

bgs = below ground surface

MAT = Mather

MW = monitoring well

2

AECOM 5-9
Table 5-3

Permanent Monitoring Well Screen Intervals, Groundwater Elevations

Site Inspection Report, Mather AASF, California

Area of 

Interest

Boring 

Location

Permanent Well 

Screen Interval 

(feet bgs)

Top of Casing 

Elevation 

(feet NAVD88)

Ground Surface 

Elevation 

(feet NAVD88)

Depth to 

Water

(feet btoc)

Depth to 

Water

(feet bgs)

Groundwater 

Elevation

(feet NAVD88)

1 MAT-MW003 112 - 122 93.07 93.55 95.08 95.56 -2.01

MAT-MW001 99 - 109 93.91 94.24 93.93 94.26 -0.02

MAT-MW002 116 - 126 92.66 93.01 96.62 96.97 -3.96

MAT-MW004 105 - 115 93.05 93.38 95.80 96.13 -2.75

MAFB-096 83.15 - 93.15 94.18 95.07 92.17 93.06 2.01

MAFB-097 101 - 111 91.42 92.29 92.39 93.26 -0.97

3 MAT-MW005 124 - 134 92.01 92.37 94.78 95.14 -2.77

4 MAT-MW006 103 - 113 90.92 91.38 95.91 96.37 -4.99

5 MAT-MW007 100 - 110 91.23 91.53 94.95 95.25 -3.72

Notes:

AASF = Army Aviation Support Facility

bgs = below ground surface

btoc = below top of casing

MAFB = Mather Air Force Base

MAT = Mather

MW = monitoirng well

NA = not applicable

NAVD88 = North American Vertical Datum 1988

2

AECOM 5-10
?!

?!

?!

?!

A!

A!

?!

?!

?!

"S "S

AOI 2

AOI 1 AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAFB-096

MAFB-097

MAT-MW005

MAT-MW006

MAT-MW007

AOI01-01

AOI01-02

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

0 200 400 800

Feet

Legend

?! Monitoring Well

A! Existing Monitoring Well

"S Surface Soil Sample

Area of Interest

Facility Boundary

Surface Water Flow Direction

Groundwater Flow Direction

Digitized Storm Drainage

Site Inspection Sample Locations

Figure 5-1

CLIENT

REVISED

SCALE

5/3/2023 MS

AP

5/3/2023

5/3/2023

ARNG

GIS BY

CHK BY

PROJECT Site Inspection at Mather AASF, CA

PM CM 5/3/2023

1:4,800 ­ 12420 Milestone Center Drive

Germantown, MD 20876

AECOM 5-11
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OM 5-12
Site Inspection Report

Mather Army Aviation Support Facility, Sacramento, California

AECOM 6-1

6. Site Inspection Results

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

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

through Section 6.7. Table 6-2 through Table 6-5 present results in soil or groundwater for the 

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

laboratory reports are provided in Appendix G. 

6.1 Screening Levels

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

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

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

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

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

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

6-1 below.

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

Analyteb

Residential

(Soil)

(μg/kg)a 

0-2 feet bgs

Industrial/ 

Commercial 

Composite 

Worker

(Soil)

(μg/kg)a 

2-15 feet bgs

Tap Water

(Groundwater)

(ng/L)a

PFOA 19 250 6 

PFOS 13 160 4

PFBS 1,900 25,000 601 

PFHxS 130 1,600 39

PFNA 19 250 6 

Notes:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Mather Army Aviation Support Facility, Sacramento, California

AECOM 6-2

6.2 Soil Physicochemical Analyses

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

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

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

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

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

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

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

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

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

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

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

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

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

6.3 AOI 1 

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

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

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

6.3.1 AOI 1 Soil Analytical Results

Soil was sampled from surface soil (0 to 2 feet bgs) from boring locations AOI01-01, AOI01-02, 

and MAT-MW003. Soil was also sampled from shallow subsurface soil (13 to 15 feet bgs) and 

deep subsurface soil intervals (110 to 112 feet bgs) from boring locations MAT-MW003. Figure 6-

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

summarize the soil results. 

The relevant compounds were detected below their SLs in at least one surface soil sample, with 

the following maximum concentrations: PFOA at 1.12 μg/kg, PFOS at 2.71 μg/kg, PFHxS at 

0.318 J μg/kg, PFNA at 0.164 J μg/kg, and PFBS at 0.161 J μg/kg. 

PFOS was detected below the SL in shallow subsurface soil, with a concentration of 

0.050 J μg/kg. The other relevant compounds were not detected in shallow subsurface soil. No

relevant compounds were detected in deep subsurface soil.

6.3.2 AOI 1 Groundwater Analytical Results 

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

summarizes the groundwater results. 

Groundwater was sampled from monitoring newly installed monitoring well MAT-MW003, 

downgradient of the suspected release area. The following detections were measured with 

regards to the SLs:

• PFOA was detected above the SL of 6 ng/L at MAT-MW003, with a concentration of

11.4 ng/L.

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

55.1 ng/L.
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Mather Army Aviation Support Facility, Sacramento, California

AECOM 6-3

• PFOS and PFBS were detected below their SLs, with a concentration of 2.91 J ng/L

and 6.19 ng/L, respectively.

• PFNA was not detected at either location.

6.3.3 AOI 1 Conclusions

Based on the results of the SI, the relevant compounds were detected in soil at concentrations 

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

SLs. Based on exceedances of the SLs in groundwater, further evaluation at AOI 1 is warranted.

6.4 AOI 2 

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

AOI 2: Airfields and AFFF Storage Areas. The results in soil and groundwater are summarized on 

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

Figure 6-7. 

6.4.1 AOI 2 Soil Analytical Results

Soil was sampled from surface soil (0 to 2 feet bgs), shallow subsurface soil (13 to 15 feet bgs),

and deep subsurface soil (between 97 to 116 feet bgs) from boring locations MAT-MW001, MATMW002, and MAT-MW004. Figure 6-1 through Figure 6-5 present the ranges of detections in 

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

PFOA, PFOS, PFHxS, and PFNA were detected below their SLs in at least one surface soil 

sample, with the following maximum concentrations: PFOA at 0.091 J μg/kg, PFOS at 1.20 μg/kg, 

PFHxS at 0.055 J μg/kg, and PFNA at 0.046 J μg/kg. PFBS was not detected in surface soil at 

AOI 2.

PFOS was detected below the SL in shallow subsurface soil at MAT-MW001, with a concentration 

of 0.097 J μg/kg. The other relevant compounds were not detected in shallow subsurface soil. No

relevant compounds were detected in deep subsurface soil.

6.4.2 AOI 2 Groundwater Analytical Results 

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

summarizes the groundwater results. 

Groundwater was sampled from newly installed monitoring wells MAT-MW001, MAT-MW002, and 

MAT-MW004 within and downgradient of the suspected release areas. Groundwater was also 

sampled from existing monitoring well MAFB-097, approximately downgradient of the Northeast 

Airfield suspected release area. The following detections were measured with regards to the SLs:

• PFOA was detected above the SL of 6 ng/L at all four wells, with concentrations ranging

from 13.7 ng/L to 123 ng/L.

• PFOS was detected above the SL of 4 ng/L at MAT-MW001 and MAT-MW002, with

concentrations of 111 ng/L and 14.2 ng/L, respectively. PFOS was detected below the

SL at MAT-MW004 and MAFB-097, with a maximum concentration of 3.07 J ng/L.

• PFHxS was detected above the SL of 39 ng/L at all four wells, with concentrations

ranging from 73.3 ng/L to 278 ng/L.

• PFNA was detected below the SL of 6 ng/L at MAT-MW001, with a concentration of

1.32 J ng/L.
Site Inspection Report

Mather Army Aviation Support Facility, Sacramento, California

AECOM 6-4

• PFBS was detected below the SL of 601 ng/L at all four wells, with a maximum

concentration of 27.9 ng/L.

6.4.3 AOI 2 Conclusions

Based on the results of the SI, the relevant compounds were detected in soil at concentrations 

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

their respective SLs. Based on exceedances of the SLs in groundwater, further evaluation at 

AOI 2 is warranted.

6.5 AOI 3 

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

AOI 3: ARNG and Air Force FTA #1. The results in soil and groundwater are presented in Table 6-

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

7. 

6.5.1 AOI 3 Soil Analytical Results

Soil was sampled from surface soil (0 to 2 feet bgs), shallow subsurface soil (13 to 15 feet bgs), 

and deep subsurface soil (122 to 124 feet bgs) from boring location MAT-MW005. Figure 6-1

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

summarize the soil results. 

PFOS and PFHxS were detected below their SLs in surface soil, with concentrations of 

0.477 J μg/kg and 0.051 J μg/kg, respectively. PFOA, PFNA, and PFBS were not detected in 

surface soil.

PFOS was detected below the SL in shallow subsurface soil, with a concentration of 

0.074 J μg/kg. The other relevant compounds were not detected in shallow subsurface soil. No 

relevant compounds were detected in deep subsurface soil.

6.5.2 AOI 3 Groundwater Analytical Results

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

summarizes the groundwater results. 

Groundwater was sampled from monitoring well MAT-MW005. The following detections were 

measured with regards to the SLs:

• PFOA was detected above the SL of 6 ng/L, with a concentration of 10.6 ng/L.

• PFHxS was detected above the SL of 39 ng/L, with a concentration of 58.4 ng/L.

• PFOS and PFBS were detected below their SLs, with concentrations of 3.71 J ng/L and

9.60 ng/L, respectively.

• PFNA was not detected.

6.5.3 AOI 3 Conclusions

Based on the results of the SI, the relevant compounds were detected in soil below their SLs. 

PFOA and PFHxS were detected in groundwater at concentrations above their SLs. Based on 

exceedances of the SLs in groundwater, further evaluation at AOI 3 is warranted.
Site Inspection Report

Mather Army Aviation Support Facility, Sacramento, California

AECOM 6-5

6.6 AOI 4 

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

AOI 4: ARNG and Air Force FTA #2. The results in soil and groundwater are presented in Table 

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

Figure 6-7. The well installed to assess AOI 4 (MAT-MW006) had to be placed downgradient of,

not within, the AOI due to airport logistics.

6.6.1 AOI 4 Soil Analytical Results

Soil was sampled from surface soil (0 to 2 feet bgs), shallow subsurface soil (13 to 15 feet bgs), 

and deep subsurface soil (101 to 103 feet bgs) from boring location MAT-MW006. Figure 6-1

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

summarize the soil results. 

PFOS was detected below the SL in surface soil, with a maximum concentration of 0.153 J μg/kg 

in the field duplicate sample (MAT-MW006-SB-0-2-D). The other relevant compounds were not 

detected in surface soil.

PFOS was detected below the SL in shallow subsurface soil, with a concentration of 

0.056 J μg/kg. The other four relevant compounds were not detected in shallow subsurface soil.

No relevant compounds were detected in deep subsurface soil. 

6.6.2 AOI 4 Groundwater Analytical Results

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

summarizes the groundwater results. 

Groundwater was sampled from monitoring well MAT-MW006. The following detections were 

measured with regards to the SLs:

• PFOA was detected above the SL of 6 ng/L, with a maximum concentration of 9.91 ng/L

in the field duplicate sample (MAT-MW006-GW-D).

• PFHxS was detected above the SL of 39 ng/L, with a maximum concentration of

66.7 ng/L in the field duplicate sample.

• PFOS and PFBS were detected below their SLs, with maximum concentrations of

2.47 J ng/L and 11.8 ng/L, respectively, in the field duplicate sample.

• PFNA was not detected in the parent or duplicate sample.

6.6.3 AOI 4 Conclusions

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

detected in groundwater, at concentrations above their SLs. Based on exceedances of the SLs in 

groundwater, further evaluation at AOI 4 is warranted. 

6.7 AOI 5

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

AOI 5: ARNG and Air Force FTA #3. The results in soil and groundwater are presented in Table 

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

Figure 6-7. The well installed to assess AOI 5 (MAT-MW007) had to be placed downgradient of,

not within, the AOI due to airport logistics.
Site Inspection Report

Mather Army Aviation Support Facility, Sacramento, California

AECOM 6-6

6.7.1 AOI 5 Soil Analytical Results 

Soil was sampled from surface soil (0 to 2 feet bgs), shallow subsurface soil (13 to 15 feet bgs), 

and deep subsurface soil (98 to 100 feet bgs) from boring location MAT-MW007. Figure 6-1

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

summarize the soil results. 

PFOA, PFOS, and PFHxS were detected below their SLs in surface soil, with concentrations of 

0.464 J μg/kg, 0.393 J μg/kg, and 0.386 J μg/kg, respectively. PFNA and PFBS were not detected 

in surface soil. No relevant compounds were detected in shallow subsurface soil. PFOS was 

detected in deep subsurface soil, with a concentration of 0.069 J μg/kg. 

6.7.2 AOI 5 Groundwater Analytical Results 

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

summarizes the groundwater results. 

Groundwater was sampled from monitoring well MAT-MW007. The following detections were 

measured with regards to the SLs:

• PFOA was detected above the SL of 6 ng/L, with a concentration of 134 ng/L.

• PFOS was detected above the SL of 4 ng/L, with a concentration of 45 ng/L.

• PFHxS was detected above the SL of 39 ng/L, with a concentration of 309 ng/L.

• PFBS was detected below the SL of 601 ng/L, with a concentrations of 34.4 ng/L.

• PFNA was not detected.

6.7.3 AOI 5 Conclusions 

Based on the results of the SI, PFOA, PFOS, and PFHxS were detected below their SLs in soil. 

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

Based on the exceedances of the SLs in groundwater, further evaluation at AOI 5 is warranted.
Table 6-2

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

Site Inspection Report, Mather Army Aviation Support Facility

Analyte OSD Screening 

Level a

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

Soil, LCMSMS compliant with QSM 5.3 Table B-15 (μg/kg)PFBS 1900 0.144 J 0.161 J ND U ND U ND U ND U ND U ND PFHxS 130 0.214 J 0.318 J ND U 0.038 J 0.055 J ND U ND U 0.PFNA 19 0.109 J 0.164 J ND U ND U 0.046 J ND U ND U NPFOA 19 0.711 J 1.12 ND U ND U 0.091 J ND U ND U NPFOS 13 1.93 2.71 0.153 J 0.234 J 1.20 0.080 J ND U 0.

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS pe

References PFHxS pe

PFNA pePFOA pe

Interpreted Qualifiers Acronyms and Abbreviations

J = Estimated concentration AASF ArU = The analyte was not detected at a level greater than or equal to the adjusted DL AOI Ar

D du

Notes DL de

ND = Analyte not detected above the LOD. LOD values are presented in Appendix F. ft fee

HQ haID ideLCMSMS liqLOD limMAT MaND anOSD OfQSM QuQual intSB soUSEPA Unμg/kg mi

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

04/01/2022

0-2 ft

MAT-MW004-SB-0-2

04/06/2022

Area of Interest

Sample ID

Sample Date

Depth

AOI01-01-SB-0-2-D

04/06/2022

0-2 ft 0-2 ft

04/06/2022

AOI01-01-SB-0-2

AOI01 

AOI01-02-SB-0-2

04/07/2022

0-2 ft 0-2 ft

MAT-MW003-SB-0-2

04/07/2022

0-2 ft

MAT-MW001-SB-0-2

04/08/2022

0-2 ft

MAT-MW002-SB-0-2

AOI02

AECOM 
Table 6-2

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

Site Inspection Report, Mather Army Aviation Support Facility

Analyte OSD Screening 

Level a

Result Qual Result Qual

Soil, LCMSMS compliant with QSM 5.3 Table B-15 (μg/kg)PFBS 1900 ND U ND UPFHxS 130 ND U 0.386 JPFNA 19 ND U ND UPFOA 19 ND U 0.464 JPFOS 13 0.153 J 0.393 J

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acidPFOA perfluorooctanoic acid

Interpreted Qualifiers Acronyms and Abbreviations

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

D duplicate

Notes DL detection limit

ND = Analyte not detected above the LOD. LOD values are presented in Appendix F. ft feet

HQ hazard quotientID identificationLCMSMS liquid chromatography with tandem LOD limit of detectionMAT MatherND analyte not detected above the LODOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierSB soil boringUSEPA United States Environmental Protecμg/kg micrograms per kilogram

Area of Interest

Sample ID

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

Depth 0-2 ft

MAT-MW006-SB-0-2-D

Sample Date 03/29/2022

AOI04 AOI05

MAT-MW007-SB-0-2

0-2 ft

04/05/2022

AECOM 
Table 6-3

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

Site Inspection Report, Mather Army Aviation Support Facility

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Q

Soil, LCMSMS compliant with QSM 5.3 Table B-15 (μg/kg)PFBS 25000 ND U ND U ND U ND U ND U ND U ND U PFHxS 1600 ND U ND U ND U ND U ND U ND U ND U PFNA 250 ND U ND U ND U ND U ND U ND U ND U PFOA 250 ND U ND U ND U ND U ND U ND U ND U PFOS 160 0.050 J 0.097 J ND U ND U ND U 0.074 J 0.056 J 

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS 

References PFHxS 

PFNA PFOA 

Interpreted Qualifiers Acronyms and Abbreviation

J = Estimated concentration AASF U = The analyte was not detected at a level greater than or equal to the adjusted DL AOI 

D 

Notes DL 

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

HQ ID LCMSMS LOD MAT ND OSD QSM Qual SB USEPA μg/kg 

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

AOI03

MAT-MW005-SB-13-15

03/30/2022

13-15 ft

04/01/2022

13-15 ft

Area of Interest

Sample ID

Sample Date

Depth

AOI01 AOI02 AOI04

MAT-MW006-SB-1

04/05/2022

13-15 ft

MAT-MW002-SB-13-15-D

04/01/2022

13-15 ft

MAT-MW004-SB-13-15

04/06/2022

13-15 ft

MAT-MW001-SB-13-15

04/08/2022

13-15 ft

MAT-MW003-SB-13-15 MAT-MW002-SB-13-15

04/07/2022

13-15 ft

AECOM 
Table 6-4

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

Site Inspection Report, Mather Army Aviation Support Facility

Area of Interest

Sample ID

Sample Date

Depth

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

Soil, LCMSMS compliant with QSM 5.3 Table B-15 (μg/kg)PFBS ND U ND U ND U ND U ND U ND U ND U NPFHxS ND U ND U ND U ND U ND U ND U ND U NPFNA ND U ND U ND U ND U ND U ND U ND U NPFOA ND U ND U ND U ND U ND U ND U ND U NPFOS ND U ND U ND U ND U ND U ND U ND U 0

Interpreted Qualifiers Chemical AbbreviationsJ = Estimated concentration PFBS pU = The analyte was not detected at a level greater than or equal to the adjusted DL PFHxS p

PFNA p

Notes PFOA p

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

Acronyms and AbbreviationsAASF AAOI AD dDL dft fID iLCMSMS lLOD lMAT MND aQSM QQual iSB sμg/kg m

AOI01

MAT-MW003-SB-110-112

04/07/2022

110-112 ft

MAT-MW005-SB-122-124

03/31/2022

122-124 ft

MAT-MW001-SB-97-99

04/08/2022

97-99 ft

AOI02

MAT-MW002-SB-114-116

04/04/2022

114-116 ft

MAT-MW004-SB-103-105

04/06/2022

103-105 ft

AOI03 AOI04

MAT-MW006-SB-101-103

04/05/2022

101-103 ft

MAT-MW005-SB-122-124-D

03/31/2022

122-124 ft

AECOM 
Table 6-5

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

Site Inspection Report, Mather Army Aviation Support Facility

Area of Interest Area of Interest

Sample ID Sample ID

Sample Date Sample Date

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Resu

PFBS 601 6.19 24.2 27.9 9.56 10.3 9.60 10.1 11.8 34.4

PFHxS 39 55.1 278 226 73.3 75.8 58.4 58.4 66.7 309

PFNA 6 ND U 1.32 J ND U ND U ND U ND U ND U ND U ND PFOA 6 11.4 123 80.1 16.5 13.7 10.6 8.33 9.91 134

PFOS 4 2.91 J 111 14.2 3.07 J 2.67 J 3.71 J 2.08 J 2.47 J 45.0

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluoro

References PFHxS perfluoro

PFNA perfluoroPFOA perfluoroPFOS perfluoro

Interpreted Qualifiers

J = Estimated concentration Acronyms and AbbreviationsU = The analyte was not detected at a level greater than or equal to the adjusted DL AASF Army Av

AOI Area of I

Notes D duplicate

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

GW groundwHQ hazard qID identificaLCMSMS liquid chLOD limit of dMAFB Mather AMAT MatherND analyte nOSD Office of QSM Quality SQual interpretUSEPA United Sng/l nanogra

MAT-MW003-GW

04/13/2022

AOI03

MAT-MW005-GW

04/14/2022

MAT-MW001-GW

04/14/2022

MAT-MW002-GW

04/16/2022

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

AOI02

MAFB-097-GW

04/16/2022

AOI01

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

AOI04 

MAT

0

MAT-MW006-GW

04/14/2022

MAT-MW006-GW-D

04/14/2022

MAT-MW004-GW

04/13/2022

AECOM 
THIS PAGE INTENTIONALLY BLANK

OM 6-12
AOI 1 AOI 2

AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAT-MW005

MAT-MW006

MAT-MW007

AOI01-01 AOI01-02

AOI 2

AOI 1

AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAT-MW005

MAT-MW006

MAT-MW007

AOI 2

AOI 1

AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAT-MW005

MAT-MW006

MAT-MW007

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-1

PFOA Detections in Soil

9/27/2023

9/27/2023

MS 9/27/2023

AP

CM

GIS BY

CHK BY

PM

9/27/2023

CLIENT

REVISED

SCALE

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ARNG

Site Inspection at Mather AASF, CA

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

the GIS User Community

1:5,400

Legend

Area of Interest

Facility Boundary

Surface Soil

Shallow Subsurface

Deep Subsurface

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

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

PFOA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

0 225 450 900

­

Feet

AECOM 6-13
AOI 2

AOI 1

AOI 3

AOI 4

AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAT-MW005

MAT-MW006

MAT-MW007

AOI01-01 AOI01-02

AOI 2

AOI 1

AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAT-MW005

MAT-MW006

MAT-MW007

AOI 2

AOI 1

AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAT-MW005

MAT-MW006

MAT-MW007

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-2

PFOS Detections in Soil

9/27/2023

9/27/2023

MS 9/27/2023

AP

CM

GIS BY

CHK BY

PM

9/27/2023

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Mather AASF, CA

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

the GIS User Community

1:5,400

Legend

Area of Interest

Facility Boundary

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

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

PFOS Results (μg/Kg)

ND

>ND - 13

>13 - 160

>160 - 1,600

>1,600

0 225 450 900

­

Feet

Surface Soil

Shallow Subsurface

Deep Subsurface

AECOM 6-14
AOI 2

AOI 1

AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAT-MW005

MAT-MW006

MAT-MW007

AOI01-01 AOI01-02

AOI 2

AOI 1

AOI 3

AOI 4

AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAT-MW005

MAT-MW006

MAT-MW007

AOI 2

AOI 1

AOI 3

AOI 4

AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAT-MW005

MAT-MW006

MAT-MW007

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-3

PFBS Detections in Soil

9/27/2023

9/27/2023

MS 9/27/2023

AP

CM

GIS BY

CHK BY

PM

9/27/2023

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Mather AASF, CA

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

the GIS User Community

1:5,400

Legend

Area of Interest

Facility Boundary

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

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

0 225 450 900

­

Feet

PFBS Results (μg/Kg)

ND

>ND - 10

>10 - 1,900

>1,900 - 25,000

>25,000

Surface Soil

Shallow Subsurface

Deep Subsurface

AECOM 6-15
AOI 2

AOI 1

AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAT-MW005

MAT-MW006

MAT-MW007

AOI01-01 AOI01-02

AOI 2

AOI 1

AOI 3

AOI 4

AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAT-MW005

MAT-MW006

MAT-MW007

AOI 2

AOI 1

AOI 3

AOI 4

AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAT-MW005

MAT-MW006

MAT-MW007

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-4

PFHxS Detections in Soil

9/27/2023

9/27/2023

MS 9/27/2023

AP

CM

GIS BY

CHK BY

PM

9/27/2023

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Mather AASF, CA

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

the GIS User Community

1:5,400

Legend

Area of Interest

Facility Boundary

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

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

0 225 450 900

­

Feet

PFHxS Results (μg/Kg)

ND

>ND - 10

>10 - 130

>130 - 1,600

>1,600

Surface Soil

Shallow Subsurface

Deep Subsurface

AECOM 6-16
AOI 2

AOI 1

AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAT-MW005

MAT-MW006

MAT-MW007

AOI01-01

AOI01-02

AOI 2

AOI 1

AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAT-MW005

MAT-MW006

MAT-MW007

AOI 2

AOI 1

AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAT-MW005

MAT-MW006

MAT-MW007

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-5

PFNA Detections in Soil

9/27/2023

9/27/2023

MS 9/27/2023

AP

CM

GIS BY

CHK BY

PM

9/27/2023

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Mather AASF, CA

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

the GIS User Community

1:5,400

Legend

Area of Interest

Facility Boundary

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

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

0 225 450 900

­

Feet

PFNA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

Surface Soil

Shallow Subsurface

Deep Subsurface

AECOM 6-17
AOI 2

AOI 1

AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAFB-097

MAT-MW005

MAT-MW006

MAT-MW007

AOI 2

AOI 1

AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAFB-097

MAT-MW005

MAT-MW006

MAT-MW007

AOI 2

AOI 1

AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAFB-097

MAT-MW005

MAT-MW006

MAT-MW007

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-6

PFOA, PFOS, and PFBS Detections

in Groundwater

8/15/2023

8/15/2023

MS 8/15/2023

AP

CM

GIS BY

CHK BY

PM

8/15/2023

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Mather AASF, CA

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

the GIS User Community

1:5,400

Legend

Area of Interest

Facility Boundary

Groundwater Flow Direction

PFOA

PFOS

PFBS

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

0 225 450 900

­

Feet

PFOA Results (ng/L)

ND

>ND - 6

>6 - 40

>40 - 70

>70

PFOS Results (ng/L(

ND

>ND - 4

>4 - 40

>40 - 70

>70

PFBS Results (ng/L)

ND

>ND - 100

>100 - 601

>601 - 2,000

>2,000

AECOM 6-18
AOI 2

AOI 1

AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAFB-097

MAT-MW005

MAT-MW006

MAT-MW007

AOI 2

AOI 1

AOI 3

AOI 4 AOI 5

MAT-MW001

MAT-MW002

MAT-MW003

MAT-MW004

MAFB-097

MAT-MW005

MAT-MW006

MAT-MW007

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-7

PFHxS and PFNA Detections

in Groundwater

8/15/2023

8/15/2023

MS 8/15/2023

AP

CM

GIS BY

CHK BY

PM

8/15/2023

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Mather AASF, CA

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

the GIS User Community

1:4,200

Legend

Area of Interest

Facility Boundary

Groundwater Flow Direction

PFHxS

PFNA

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

PFHxS Results (ng/L)

ND

>ND - 39

>39 - 100

>100 - 1,000

>1,000

PFNA Results (ng/L)

ND

>ND - 6

>6 - 100

>100 - 1,000

>1,000

0 175 350 700

­

Feet

AECOM 6-19
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nspection Report

er Army Aviation Support Facility, Sacramento, California
Site Inspection Report

Mather Army Aviation Support Facility, Sacramento, California

AECOM 7-1

7. Exposure Pathways

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

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

be impacted, the decision to move from SI to RI or interim action is determined based upon 

exceedances of the SLs for the relevant compounds and whether the release is more than likely 

attributable to the DoD. A CSM presents the current understanding of the site conditions with 

respect to known and suspected sources, potential transport mechanisms and migration 

pathways, and potentially exposed human receptors. A human exposure pathway is considered 

potentially complete when the following conditions are present:

1. Contaminant source;

2. Environmental fate and transport;

3. Exposure point;

4. Exposure route; and

5. Potentially exposed populations.

If any of these elements are missing, the pathway is incomplete. The CSM figures use an empty 

circle symbol to represent an incomplete exposure pathway. Areas with an incomplete pathway 

generally warrant no further action. However, the pathway is considered potentially complete if the 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

boundary, and recreational users outside of the facility boundary.

7.1 Soil Exposure Pathway

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

between the source and potential receptors at AOI 1 through AOI 5 based on the aforementioned 

criteria.

7.1.1 AOI 1 

AOI 1 is the Wash Rack, where one instance of a fire training exercise occurred in approximately 

2010 and may have resulted in a potential AFFF release. 

The relevant compounds were detected below their SLs in surface and shallow subsurface soil at 

AOI 1. Site workers and construction workers could contact constituents in surface soil via 
Site Inspection Report

Mather Army Aviation Support Facility, Sacramento, California

AECOM 7-2

incidental ingestion and inhalation of dust. Therefore, the surface soil exposure pathway for site 

workers, future construction workers and trespassers are potentially complete. Construction 

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

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

AOI 1 is presented on Figure 7-1. 

7.1.2 AOI 2 

AOI 2 consists of the Airfields and AFFF Storage areas, where familiarization training exercised 

with Tri-MaxTM fire extinguishers took place and storage areas contained Tri-MaxTM units and 

AFFF.

The relevant compounds were detected below their SLs in surface and shallow subsurface soil at 

AOI 2. Site workers, construction workers and trespassers could contact constituents in surface 

soil via incidental ingestion and inhalation of dust. Therefore, the surface soil exposure pathway 

for site workers and future construction workers are potentially complete. Construction workers 

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

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

AOI 2 is presented on Figure 7-1. 

7.1.3 AOI 3 

AOI 3 is the ARNG and Air Force FTA #1, where combined ARNG and Air Force extraction type 

exercises may have involved extinguishing live fire with either water or an unknown type of foam.

The relevant compounds were detected below their SLs in surface and shallow subsurface soil at 

AOI 3. Site workers, construction workers and trespassers could contact constituents in surface 

soil via incidental ingestion and inhalation of dust. Therefore, the surface soil exposure pathway 

for site workers and future construction workers are potentially complete. Construction workers 

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

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

AOI 3 is presented on Figure 7-1. 

7.1.4 AOI 4 

AOI 4 is the ARNG and Air Force FTA #2, where combined ARNG and Air Force extraction type 

exercises may have involved extinguishing live fire with either water or an unknown type of foam.

PFOS was detected below the SL in surface and shallow subsurface soil at AOI 4. Site workers, 

construction workers and recreational users/trespassers could contact constituents in surface soil 

via incidental ingestion and inhalation of dust. Therefore, the surface soil exposure pathway for 

site workers and future construction workers are potentially complete. Construction workers could 

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

exposure pathway for construction workers is potentially complete. The CSM for AOI 4 is 

presented on Figure 7-1. 

7.1.5 AOI 5 

AOI 5 is the ARNG and Air Force FTA #3, where combined ARNG and Air Force extraction type 

exercises may have involved extinguishing live fire with either water or an unknown type of foam.

The relevant compounds were detected in surface soil at AOI 5. Site workers, construction 

workers and recreational users/trespassers could contact constituents in surface soil via 

incidental ingestion and inhalation of dust. Therefore, the surface soil exposure pathway for site 

workers and construction workers are potentially complete. No relevant compounds were 
Site Inspection Report

Mather Army Aviation Support Facility, Sacramento, California

AECOM 7-3

detected in shallow subsurface soil, and therefore, the subsurface soil exposure pathway for 

construction workers is considered incomplete. The CSM for AOI 5 is presented on Figure 7-2.

7.2 Groundwater Exposure Pathway

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

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

7.2.1 AOI 1 through AOI 5

PFOA, PFOS, and/or PFHxS were detected above their SLs in groundwater samples collected at 

AOI 1 through AOI 5. Due to the presence of public water supply wells located southwest (i.e., 

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

groundwater is considered potentially complete. The facility drinking water supply wells are 

located cross-gradient, approximately 2 miles south of the AASF; therefore, the exposure pathway 

for groundwater to the site worker via ingestion of groundwater is considered incomplete. Depths 

to water measured in April 2022 during the SI ranged from 93.06 to 96.97 feet bgs; therefore, 

construction workers would not reasonably encounter groundwater, and the ingestion exposure 

pathway for future construction workers is considered incomplete. The CSM for AOI 1, AOI 2, AOI 

3, and AOI 4 is presented on Figure 7-1, and the CSM for AOI 5 is presented on Figure 7-2.

7.3 Surface Water and Sediment Exposure Pathway

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

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

between the source and potential receptors.

7.3.1 AOI 1

PFAS are water soluble and can migrate readily from soil to surface water via leaching and runoff. Because the relevant compounds were detected in soil at AOI 1, it is possible that those 

compounds may have migrated from soil to surface water. The drains in the wash rack area led

to an oil water separator and then flow into the sanitary sewer system. Therefore, potential 

discharges of AFFF in the wash rack would primarily release directly into the sanitary sewer 

system. However, any runoff not captured by the oil water separator could reach nearby surface 

drainages that lead into tributaries of the Sacramento River. Due to recreational use of the 

Sacramento River, the surface water and sediment exposure pathway for recreational users is 

considered potentially complete. No surface water bodies are present on the facility; therefore, 

the surface water and sediment ingestion exposure pathway for site workers and construction 

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

7.3.2 AOI 2

Because the relevant compounds were detected in soil at AOI 2, it is possible that those 

compounds may have migrated from soil to surface water. While large scale watershed maps 

show AOI 2 lies within the Lake Greenhaven-Sacramento River Watershed, constructed drainage 

systems direct water to the Upper Morrison Creek Watershed, and surface water from the entire 

AASF is drained by tributaries to the Sacramento River. Due to recreation use of the Sacramento 

River, the surface water and sediment exposure pathway for recreational users is considered 

potentially complete. The Northeast Airfield drains via constructed drainage systems to the South 

Canal, and then to Morrison Creek and eventually the Sacramento River. No surface water bodies 

are present on the facility; therefore, the surface water and sediment ingestion exposure pathway 
Site Inspection Report

Mather Army Aviation Support Facility, Sacramento, California

AECOM 7-4

for site workers and construction workers is considered incomplete. The CSM for AOI 2 is 

presented on Figure 7-1. 

7.3.3 AOI 3, AOI 4, and AOI 5 

AOI 3, AOI 4, and AOI 5 are located on paved surfaces, where potential releases of surface water 

run-off may drain into stormwater inlets that drain into tributaries of the Sacramento River. 

Therefore, the surface water and sediment exposure pathway for recreational users is considered 

potentially complete. AOI 3, AOI 4, and AOI 5 are located off-facility, therefore, the surface water 

and sediment exposure pathway for site workers and construction workers is considered 

incomplete. The CSM for AOI 3 and AOI 4 is presented on Figure 7-1, and the CSM for AOI 5 is 

presented on Figure 7-2. 
Media

SOURCE PATHWAY RECEPTOR

AOI 1

AOI 2

AOI 3

AOI 4

Fire Training, Fire

Extinguishers

Discharge, and

AFFF Storage

Surface soil

Human

activities

Precipitation/

run-off

Leaching/

infiltration

Airborne soil

particulate

Surface soil

at AOI

Surface

water/

sediment

Subsurface

soil

Shallow

groundwater

Source Release

Mechanism Media Transportand Migration Media ExposureRoutes

Inhalation of

dust

Ingestion

Ingestion

Ingestion

Ingestion

Human Receptors:

Current/ Future

Flow-Chart Continues

Partial/ Possible Flow

Flow-Chart Stops

Incomplete Pathway

Potentially Complete Pathway

Potentially Complete Pathway

with Exceedance of SL

/ / / /

Site 

Worker

Construction 

Worker3 Resident1,2 Trespasser/ Recreational User1

Site 

Worker

Construction 

Worker3 Resident1,2

/ / / /

/ / / /

/ / / /

/ / / /

LEGEND

Figure 7-1

Conceptual Site Model, AOI 1 through AOI 4

Mather AASF

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

Trespasser/ 

Recreational User1

1. The resident and recreational users refer to offsite receptors.

2. Inhalation of dust for off-site receptors is likely

insignificant.

3. No current active construction at the facility.

Notes:

AECOM 7-5
Media

SOURCE PATHWAY RECEPTOR

AOI 5 Fire Training Surface soil

Human

activities

Precipitation/

run-off

Leaching/

infiltration

Airborne soil

particulate

Surface soil

at AOI

Surface

water/

sediment

Subsurface

soil

Shallow

groundwater

Source Release

Mechanism Media Transportand Migration Media ExposureRoutes

Inhalation of

dust

Ingestion

Ingestion

Ingestion

Ingestion

Human Receptors:

Current/ Future

Flow-Chart Continues

Partial/ Possible Flow

Flow-Chart Stops

Incomplete Pathway

Potentially Complete Pathway

Potentially Complete Pathway

with Exceedance of SL

/ / / /

Site 

Worker

Construction 

Worker3 Resident1,2 Trespasser/ Recreational User1

Site 

Worker

Construction 

Worker3 Resident1,2

/ / / /

/ / / /

/ / / /

/ / / /

LEGEND

Figure 7-2

Conceptual Site Model, AOI 5

Mather AASF

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

Trespasser/ 

Recreational User1

1. The resident and recreational users refer to offsite receptors.

2. Inhalation of dust for off-site receptors is likely

insignificant.

3. No current active construction at the facility.

Notes:

AECOM 7-6
Site Inspection Report

Mather Army Aviation Support Facility, Sacramento, California

AECOM 8-1

8. Summary and Outcome

This section summarizes SI activities and findings. The most significant findings are summarized 

in this section and are reproduced directly or abstracted from information contained in this report. 

The outcome provides general and comparative interpretations of the findings relative to the SLs. 

8.1 SI Activities 

The SI field activities were conducted from 28 March 2022 to 16 April 2022 and consisted of utility 

clearance, hand augering, sonic boring, soil sample collection, permanent monitoring well 

installation, groundwater sample collection, and land surveying. Field activities were conducted in 

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

Section 5.8. 

To fulfill the project DQOs set forth in the approved SI QAPP Addendum (AECOM, 2021), samples 

were collected and analyzed for a subset of 18 compounds by LC/MS/MS compliant with QSM 5.3 

Table B-15 as follows.

• Twenty-three (23) soil samples from seven boring locations and two hand auger locations;

• Eight groundwater samples from eight permanent monitoring wells;

• Sixteen (16) QA/QC samples.

An SI is conducted when the PA determines an AOI exists based on probable use, storage, and/or 

disposal of PFAS-containing materials. The SI includes multi-media sampling at AOIs to 

determine whether or not a release has occurred. The SI may conclude further investigation is 

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

required. Additionally, the CSMs were refined to assess whether a potentially complete pathway 

exists between the source and potential receptors for potential exposure at the AOIs, which are 

described in Section 7. 

8.2 Outcome

Based on the results of this SI, further evaluation under CERCLA is warranted in an RI for each 

of the five AOIs. Based on the CSMs developed and revised in light of the SI findings, there is 

potential for exposure to drinking water receptors from each of the five AOIs from sources on and 

adjacent to the facility resulting from historical DoD activities. Sample analytical concentrations 

collected during the SI were compared to the project SLs in soil and groundwater, as described 

in Table 6-1. A summary of the results of the SI data relative to the SLs is as follows:

• At AOI 1:

• The detected concentrations of the relevant compounds in soil at AOI 1 were below

their SLs.

• PFOA and PFHxS in groundwater exceeded their SLs. PFOA exceeded its SL of 6

ng/L, with a concentration of 11.4 ng/L at location MAT-MW003. PFHxS exceeded

its SL of 39 ng/L, with a concentration of 55.1 ng/L at location MAT-MW003. The

detected concentrations of the other relevant compounds were below their SLs.

• Based on exceedances of SLs in groundwater, further evaluation of AOI 1 is

warranted in an RI.

• At AOI 2:
Site Inspection Report

Mather Army Aviation Support Facility, Sacramento, California

AECOM 8-2

• The detected concentrations of the relevant compounds in soil at AOI 2 were below

their SLs.

• PFOA, PFOS, and PFHxS in groundwater exceeded their SLs. PFOA exceeded its

SL of 6 ng/L, with a maximum concentration of 123 ng/L at MAT-MW001. PFOS

exceeded the SL of 4 ng/L, with a maximum concentration of 111 ng/L at location

MAT-MW001. PFHxS exceeded the SL of 39 ng/L, with a maximum concentration of

278 ng/L at location MAT-MW001. The detected concentrations of the other relevant

compounds were below their SLs.

• Based on exceedances of SLs in groundwater, further evaluation of AOI 2 is

warranted in an RI.

• At AOI 3:

• The detected concentrations of relevant compounds in soil at AOI 3 were below their

SLs.

• PFOA and PFHxS in groundwater exceeded their SLs at location MAT-MW005.

PFOA exceeded its SL of 6 ng/L, with a concentration of 10.6 ng/L. PFHxS exceeded

its SL of 39 ng/L, with a concentration of 58.4 ng/L. The detected concentrations of

the other relevant compounds were below their SLs.

• Based on exceedances of SLs in groundwater, further evaluation of AOI 3 is

warranted in an RI.

• At AOI 4:

• The detected concentrations of relevant compounds in soil at AOI 4 were below their

respective SLs.

• PFOA and PFHxS in groundwater exceeded their SLs at location MAT-MW006.

PFOA exceeded the SL of 6 ng/L, with a maximum concentration of 9.91 ng/L in the

field duplicate sample. PFHxS exceeded the SL of 39 ng/L, with a concentration of

66.7 ng/L in the field duplicate sample. The detected concentrations of the other

relevant compounds were below their SLs.

• Based on exceedances of SLs in groundwater, further evaluation of AOI 4 is

warranted in an RI.

• At AOI 5:

• The detected concentrations of relevant compounds in soil at AOI 5 were below their

SLs.

• PFOA, PFOS, and PFHxS in groundwater exceeded their SLs at location MATMW007. PFOA exceeded its SL of 6 ng/L, with a concentration of 134 ng/L. PFOS

exceeded its SL of 4 ng/L, with a concentration of 45 ng/L. PFHxS exceeded its SL

of 39 ng/L, with a concentration of 309 ng/L. The detected concentrations of the other

relevant compounds were below their SLs.

• Based on exceedances of SLs in groundwater, further evaluation of AOI 5 is

warranted in an RI.

Of the six PFAS compounds presented in the 6 July 2022 OSD memorandum, HFPO-DA 

(commonly referred to as GenX) was not included as an analyte at the time of this SI. Based on 

the CSM developed during the PA and revised based on SI findings, the presence of HFPO-DA 

is not anticipated at the facility because HFPO-DA is generally not a component of MIL-SPEC 
Site Inspection Report

Mather Army Aviation Support Facility, Sacramento, California

AECOM 8-3

AFFF and based on its history including distribution limitations that restricted use of GenX, it is 

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

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

Table 8-1 summarizes the SI results for soil and groundwater used to determine if an AOI should 

be considered for further investigation under CERCLA and undergo an RI.

Table 8-1: Summary of Site Inspection Findings and Recommendations

AOI Potential 

Release Area

Soil –

Source Area

Groundwater –

Source Area

Groundwater –

Facility Boundary Future Action

1 Wash Rack Proceed to RI

2 Airfields and AFFF 

Storage Areas Proceed to RI

3 ARNG and Air 

Force FTA #1 N/A Proceed to RI

4 ARNG and Air 

Force FTA #2 N/A Proceed to RI

5 ARNG and Air 

Force FTA #3 N/A Proceed to RI

Legend:

N/A = not applicable

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected
Site Inspection Report

Mather Army Aviation Support Facility, Sacramento, California

AECOM 8-4

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Mather Army Aviation Support Facility, Sacramento, California

AECOM 9-1

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(PFOA) Impacted Sites ARNG Installations, Nationwide. March. 

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sediments. Environmental Science and Technology 40 (23): 7251-7256.

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2000.

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USFWS. 2022. Species by County Report, County: Sacramento, California. Environmental 

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and perfluorooctanoate (PFOA) in soils and groundwater of a U.S. metropolitan area: 

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Mather Army Aviation Support Facility, Sacramento, California

AECOM 9-4

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