FINAL

Site Inspection Report 

Camp San Luis Obispo

San Luis Obispo, 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..............................................................................................2-3

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

2.2.4 Climate........................................................................................................2-4

2.2.5 Current and Future Land Use......................................................................2-5

2.2.6 Sensitive Habitat and Threatened/ Endangered Species.............................2-5

2.3 History of PFAS Use..............................................................................................2-6

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

3.1 AOI 1 Former Cal FIRE Training Area ...................................................................3-1

3.2 AOI 2 Former META Yard Fire Training Area .........................................................3-1

3.3 AOI 3 Cal FIRE Cuesta Camp Tenant ...................................................................3-1

3.4 AOI 4 O’Sullivan Airfield Shed ...............................................................................3-1

3.5 AOI 5 de Havilland Beaver Crash Site...................................................................3-1

3.6 AOI 6 Fuel Point....................................................................................................3-2

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 Temporary Well Installation and Groundwater Grab Sampling...............................5-4

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

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

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

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

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

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

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

6.7 AOI 6.....................................................................................................................6-4

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

6.7.2 AOI 6 Conclusions ......................................................................................6-5

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

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

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

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

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

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

7.1.5 AOI 6...........................................................................................................7-2

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

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

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

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

7.3.1 AOI 1, AOI 2, AOI 3, and AOI 6 ...................................................................7-3

7.3.2 AOI 4...........................................................................................................7-3

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

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

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

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

Appendix A Data Usability Assessment and Validation Reports

Appendix B Field Documentation

B1. Log of Daily Notice of Field Activities

B2. Field Change Request Forms

B3. Nonconformance and Corrective Action Reports

B4. Survey Data

Appendix C Photographic Log

Appendix D TPP Meeting Minutes

Appendix E Boring Logs

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, June 2021

Figure 2-5 Surface Water Features

Figure 3-1 Areas of Interest

Figure 5-1 Site Inspection Sample Locations

Figure 6-1 PFOA Detections in Soil

Figure 6-2 PFOS Detections in Soil

Figure 6-3 PFBS Detections in Soil

Figure 6-4 PFHxS Detections in Soil

Figure 6-5 PFNA Detections in Soil

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

Figure 6-7 PFHxS and PFNA Detections in Groundwater

Figure 7-1 Conceptual Site Model, AOI 1

Figure 7-2 Conceptual Site Model, AOI 2

Figure 7-3 Conceptual Site Model, AOI 3 and AOI 6

Figure 7-4 Conceptual Site Model, AOI 4

Tables

Table ES-1 Screening Levels (Soil and Groundwater)

Table ES-2 Summary of Site Inspection Findings and Recommendations

Table 5-1 Site Inspection Samples by Medium

Table 5-2 Soil Boring Depths, Temporary 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

AECOM AECOM Technical Services, Inc.

AFFF aqueous film-forming foam

AOI Area of Interest

ARNG Army National Guard

bgs below ground surface 

CAARNG California Army National Guard

Cal Poly California Polytechnic State University

Camp SLO Camp San Luis Obispo

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act 

CMC California Men’s Colony

CoC chain of custody

CSLRCD Coastal San Luis Resource Conservation District

CSM conceptual site model

DA Department of the Army

DoD Department of Defense

DPT direct push technology

DQO data quality objective

DUA data usability assessment

ELAP Environmental Laboratory Accreditation Program

EM Engineer Manual

FedEx Federal Express

FTA Fire Training Area

gpm gallons per minute

GPRS Ground Penetrating Radar Systems

GSA General Services Administration

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

MBNEP Morro Bay National Estuary Program

META Motorized Equipment Training Academy

MIL-SPEC military specification

MS matrix spike

MSD matrix spike duplicate

NELAP National Environmental Laboratory Accreditation Program

ng/L nanograms per liter

NOAA National Oceanic and Atmospheric Administration

OSD Office of the Secretary of Defense
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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

RWQCB Regional Water Quality Control Board

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 six Areas of Interest (AOIs) where PFAS-containing materials may have been 

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

of the SI is to identify whether there has been a release to the environment from the AOIs identified

in the PA and determine whether further investigation is warranted, a removal action is required 

to address immediate threats, or no further action is required based on SLs for relevant 

compounds. This SI was completed at Camp San Luis Obispo (Camp SLO) in San Luis Obispo, 

California and determined further investigation is warranted for AOI 1: Former Cal FIRE Fire 

Training Area (FTA) and AOI 2: Former Motorized Equipment Training Academy (META) Yard 

FTA. Camp SLO will also be referred to as the “facility” throughout this document. 

Camp SLO occupies approximately 5,320 acres along the northern and southern sides of and 

adjacent to Highway 1, extending from Cerro Romualdo and Chumash Peak in the southern 

portion, to the foothills of the Santa Lucia Range in the northern portion of the facility. The facility 

supports federal and state military training activities and serves as a year-round training site for 

the California ARNG. 

The PA identified six AOIs, five of which were investigated 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 for AOI 1: Former Cal FIRE FTA and AOI 2: Former META Yard FTA; no further 

evaluation is warranted for AOI 3, AOI 4, AOI 5, and AOI 6 at this time.

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 Former CAL 

FIRE FTA Proceed to RI 

2

Former 

META Yard 

FTA

Proceed to RI

3

CAL FIRE 

Cuesta 

Camp 

Tenant

N/A N/A No further 

action

4 O’Sullivan 

Airfield Shed N/A N/A No further action

6 Fuel Point N/A N/A No further 

action

Legend:

N/A = not applicable 

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= 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 Camp San Luis Obispo 

(SLO) in San Luis Obispo, California. Camp SLO 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 Camp SLO (AECOM Technical Services, Inc. [AECOM], 2020) that

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

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

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

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

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

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

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

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

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

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

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

2.1 Facility Location and Description

Camp SLO is located in southern San Luis Obispo County in central California, approximately 6.5 

miles east of the Pacific Ocean and 5 miles northwest of the City of San Luis Obispo (Figure 2-

1). The facility occupies approximately 5,320 acres along the northern and southern sides of 

Highway 1, extending from Cerro Romualdo and Chumash Peak in the southern portion, to the 

foothills of the Santa Lucia Range in the northern portion of the facility.

Camp SLO was originally established by California in 1929, on 5,800 acres, as a National Guard 

Training Camp known as Camp Merriam. In 1940, Congress authorized funds for the Army to 

lease about 44,000 acres of ranch lands and eventually purchased the leased parcels and 

additional lands in 1943. Construction of the Main Garrison began on 15 November 1940. Camp 

SLO officially began its mission as a training site in March 1941 (Camp Roberts Historical 

Museum, 2020).

From 1939 to 1945, Camp SLO served as a California ARNG (CAARNG) training site for horse 

cavalry, and the Navy also likely used the area for live-fire training activities during World War II. 

In 1947, control of the Camp reverted to CAARNG, and the US Army operated the Southwest 

Signal Center at Camp SLO in 1951 during the Korean conflict. Part of Camp SLO remained 

under federal control until 1 July 1965, when the entire property was returned to State control. 

Approximately 4,685 acres were relinquished to the General Services Administration (GSA) in 

1965. The GSA then transferred the property to other agencies and individuals beginning in the 

late 1960s through the 1980s. Most of the property was transferred to California Polytechnic State 

University (Cal Poly) and Cuesta College for educational use. A total of 5,880 acres were retained 

by the CAARNG for the purpose of developing a training facility for CAARNG.

Camp SLO supports federal and state military training activities and serves as a year-round 

training site for the CAARNG. Access to the facility is restricted and inaccessible to the general 

public in some areas. The facility’s mission is to maintain and allocate training areas, airspace, 

facilities, and ranges in order to support CAARNG. Additionally, the facility provides quality of life, 

logistical support to training units, and administrative services. Future land use is not anticipated 

to change.

2.2 Facility Environmental Setting

Camp SLO is located on the western slopes of the Santa Lucia Range, approximately 4.5 miles

and 6.5 miles east of Morro Bay and the Pacific Ocean, respectively. The terrain in and around

the facility is primarily the foothills of the Santa Lucia Range, which exhibits high relief with

grasslands, rolling hills, and canyons. The facility is bounded to the north by Los Padres National

Forest in the Santa Lucia Mountains and to the south by Cerro Romualdo and Chumash Peak,

two hills that are a part of the Nine Sisters Peaks. The elevation of the facility ranges from

approximately 190 feet to 2,440 feet above mean sea level, with elevation increasing from west 

to east (Figure 2-2). 

2.2.1 Geology

Camp SLO lies within the Pacific Border physiographic province, California Coast Ranges. The 

California Coast Ranges are predominantly composed of late Mesozoic and Cenozoic 

sedimentary rocks (Franciscan Complex) formed from subduction of the Pacific Plate under the 

North American Plate. The landscape also displays lateral deformation from the San Andreas 

Fault System, which dominates the California Coast Ranges, resulting in parallel sequences of 
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linear ridges and valleys (Fuller, M. et al., 2015). The various geologic formations and features at 

Camp SLO and within the surrounding area are presented in Figure 2-3. 

The majority of Camp SLO lies on the Franciscan Complex, which is a mélange of Cretaceous to 

Jurassic-age fragmented rock masses in a sheared matrix of argillite and crushed 

metasandstone. Individual rock masses within the mélange range in size from less than a meter 

to kilometers. Blocks large enough to map include sandstone and shale in the western portion of 

the facility and metavolcanic rocks in the south and central portions of the facility. The sandstone 

and shale are made up of fine- to medium-grained greywacke sandstone interbedded with shale 

and siltstone. The metavolcanic rocks are primarily greenstone metamorphosed from basalt. The 

Jurassic-age, serpentinized, ultramafic rocks lie on the north side of the Franciscan Complex, 

bounded on both sides by faults and composed of pervasively sheared serpentinite (Wiegers, 

M.O., 2010).

Oligocene and Miocene-aged rocks unconformably lie above the Franciscan Complex and are 

composed of the Rincon Shale, the Obispo Formation, and the Monterey Formation. The Rincon 

Shale is located on the east side of the Chorro Reservoir and comprises primarily siltstone and 

silty claystone and locally contains zones of dolomite and arkosic sandstone. The Obispo 

Formation lies above the Rincon Shale to the northeast and is composed primarily of fine- to 

coarse-grained vitric tuff. The Monterey Formation begins just north of the Chorro Reservoir and 

is composed of laminated to thin-bedded shale, siliceous claystone, and soft diatomaceous 

siltstone (Wiegers, M.O., 2010).

Holocene and Pleistocene landslide deposits overlie the Monterey Formation and occupy the 

northeastern portion of the facility. The landslide complex is deeply dissected in a serpentinite and 

diabase dike-and-sill complex on the southwest side of the Santa Lucia Range (Wiegers, M.O., 

2010). The Oceanic Fault is a reverse fault that strikes west-northwest, stretches from Santa 

Maria to its convergence with the San Simeon Fault, just northwest of San Simeon, and runs 

through the northern side of the landslide deposits. Additional, smaller faults appear in the area 

as right-lateral, strike-slip faults with near vertical fault planes.

The Morro Rock – Islay Hill Volcanic Intrusive Complex forms a series of volcanic plugs and lava 

domes known as the Nine Sisters Peaks. Two of the peaks (Cerro Romualdo and Chumash Peak) 

are located in the southern side of Camp SLO along the facility boundary. The Morro Rock – Islay 

Hill Volcanic Intrusive Complex (Oligocene) is composed of porphyritic dacite, with flow banding 

common (Wiegers, M.O., 2010). The Intrusive Complex penetrates the Franciscan Complex, with 

the Franciscan Complex mélange on the slopes of Cerro Romualdo, and the Franciscan Complex 

sandstone and shale on the north slope of Chumash Peak.

The westernmost portion of the facility is composed of young Holocene to late Pleistocene alluvial 

flood-plain deposits of unconsolidated sand, silt, and clay. These alluvial deposits are observed 

as thick as 50 feet and found along Chorro Creek as well as several other unnamed streams 

traversing the facility. The remaining unconsolidated overburden is also observed as thick as 50 

feet and is primarily composed of silt and clay terrace deposits.

Soil borings completed during the SI found silty sand and lean clay as the dominant lithology of 

the unconsolidated sediments below Camp SLO and are consistent with the alluvial and floodplain deposits described in the region. The borings were completed at depths between 30 and 

100 feet below ground surface (bgs). In the shallower portions of the borings, isolated layers of 

silt and gravel were also observed in the boring logs at thicknesses ranging from 0.5 to 9 feet. 

Many of the logs also reported varying percentages of gravel included in the sand packages. 

These results and facility observations are consistent with the understood localized use of fill 

material and the alluvial depositional environment. The original estimated depth to water was 

assumed to be 30 feet bgs, based on historical information. During the second mobilization, a 

maximum depth of 100 feet bgs was selected for drilling, given the lack of any moisture observed 
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in the overburden and the challenging drilling conditions. These deeper borings were dominated 

by fine-grain materials (smectitic clay-dominated) consistent with the volcanic deposits in the 

region. Boring logs are presented in Appendix E. 

2.2.2 Hydrogeology

Regional groundwater flow is to the west, towards the Chorro Valley Groundwater Basin and 

Morro Bay. Groundwater in the region is found in Pleistocene to Holocene age surficial deposits. 

The primary source of groundwater extracted from wells in the region is from generally thin 

alluvium deposits that blanket the San Luis Obispo Creek watershed. Recharge to the 

groundwater basin is from applied irrigation water, influence from streams, and infiltration of 

precipitation on the valley (State of California, 2004).

Both the City of San Luis Obispo and San Luis Obispo County extract groundwater from the San 

Luis Obispo Valley Groundwater Basin, located to the south and east of the facility. The northwest 

boundary of the San Luis Obispo Valley Groundwater Basin contacts the impermeable Franciscan 

Group rocks approximately 1 mile south of the facility. Based on available information, domestic 

and private supply wells are located within 2 miles of the facility (Figure 2-3) (AECOM, 2020; 

California State Water Resources Control Board, 2022). 

Camp SLO is not located on a principal aquifer system, and the underlying bedrock formations 

are not generally recognized as water bearing. Groundwater is primarily found in the Holocene to 

late Pleistocene alluvial flood-plain deposits. Yields from the alluvial deposits are generally from 

20 gallons to 300 gallons per minute (gpm), and yields from the terrace deposits are generally 

around 20 gpm (State of California, 2004).

The three water wells at Camp SLO that were historically used for potable water purposes include 

Well No’s 1, 2, and 3 (see Figure 2-3). Well No. 1 is 12-inches in diameter and approximately 51 

feet bgs. No construction information is available for Wells No. 2 and 3 (Geosystems Consultants, 

Inc., 1996). According to the Camp SLO Environmental Scientist, the wells are without pumping 

equipment and are currently managed by San Luis Obispo County, who use the wells to gauge 

and monitor groundwater basin conditions (i.e., depth to groundwater). According to California 

Regional Water Quality Control Board (RWQCB), the nearest public water supply well is located 

approximately 4.1 miles from Camp SLO. Private properties in the Chorro Creek valley rely on 

private domestic wells for their water supply (RWQCB Comments on AECOM, 2021b).

Depth to water was measured in June 2021 from the newly installed wells that contained water. 

Only four of the seven wells installed contained water, and water levels ranged from 31.65 to 

34.95 feet bgs. Groundwater elevation contours from the SI are presented on Figure 2-4 and 

indicate groundwater flow direction is generally to the northwest. 

2.2.3 Hydrology 

The majority of Camp SLO is within the Morro Bay Watershed, which is located in the central area 

of coastal San Luis Obispo County and covers an area of approximately 46,598 acres (Morro Bay 

National Estuary Program [MBNEP], 2013). Surface water features and watersheds are 

presented in Figure 2-5. 

The watershed has two major sub-watersheds that drain to Chorro and Los Osos Creeks, both of 

which drain to the Morro Bay Estuary and then to the Pacific Ocean. The Chorro Creek subwatershed, within which the majority of Camp SLO is situated, accounts for about 60 percent (%) 

of the total land area that drains to the Morro Bay Estuary (MBNEP, 2013). Relatively small land 

surface areas along the southeastern and eastern margins of Camp SLO are situated within the 

Upper and Lower San Luis Obispo Creek Watersheds, respectively. Water in the Morro Bay 
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watershed is managed by the City of Morro Bay, Los Osos Community Services District, Golden 

State Water Company, and S&T Mutual Water Company (MBNEP, 2013). 

Regional surface water features include Chorro Creek, which passes through the facility, and 

Chorro Reservoir, which is located in the northeastern portion of the facility. The Chorro Creek is 

a 2002 303(d)-listed impaired waterbody that flows into a Marine Protected Area (Morro Bay State 

Estuary and MBNEP) and is designated as a critical coastal area along the central coast of 

California (California Coastal Commission, 2016). Sixty (60) % of the Chorro Creek watershed is 

classified as rangeland, and 20% is brushland.

Chorro Creek is regionally used for domestic and municipal water supply and agricultural supply 

purposes. Chorro Reservoir was used for hydroelectric power generation and recreation. It is 

operated by the California Men’s Colony (CMC). The reservoir was constructed in 1941 to store 

runoff water for Camp SLO and was historically used for the facility’s water supply along with 

three base wells. 

The potable water supply for Camp SLO is from waters piped to the facility from Chorro Reservoir

and Whale Rock Reservoir, which is situated approximately 11 miles to the northwest of the

facility. The water is piped to a water treatment facility located at Chorro Reservoir, where after

treatment, water is distributed to the Camp SLO, SLO County Facilities, and Cuesta College. The

treatment facility is managed by the CMC. The CMC and Cuesta College also receive State Water

through the Chorro Valley Turnout. The Turnout conveys State Water from the Coastal Branch of

the State Water pipeline to the CMC (MBNEP, 2013). Potable water for the coastal town of Los

Osos (4 miles downgradient of Camp SLO) is provided from several groundwater wells.

The main surface water drainage feature for Camp SLO is Chorro Creek, which begins to the

north of the facility, passes through the center of the facility in a northeast-southwest direction,

and exits the facility on the southwest boundary. Chorro Creek is a fifth order stream and has

approximately 14.2 miles of blue line stream (Coastal San Luis Resource Conservation District

[CSLRCD], 2001). Tributaries of Chorro Creek at and within the vicinity of Camp SLO are

intermittent and flow only when precipitation is sufficient. Chorro Creek flows into the Chorro

Reservoir (visible on Figure 2-2), after which it passes beneath Highway 1 and flows through all 

of the cantonment areas of Camp SLO. Downstream of Camp SLO, Chorro Creek converges with 

the Morro Bay Estuary located approximately 7 miles west of the facility. Chorro Creek is fed by 

numerous small tributary streams that flow through the facility. These streams include Dairy 

Creek, which originates just north of the property boundary, cuts across the northwest corner of 

the facility, and parallels the western property boundary until it converges with Chorro Creek in 

the southern portion of the facility.

According to the National Wetlands Inventory by the US Fish and Wildlife Service, emergent or 

forested/shrub wetlands are located at Camp SLO around Chorro Reservoir. Figure 2-5 depicts 

the locations of the wetland areas. The wetlands in the reservoir area are generally 

noncontiguous, each less than about 2 acres in extent. Forested/shrub and emergent wetlands 

areas exist in nearly all areas adjacent to Chorro Creek and its tributaries, within the various 

creeks’ stream banks.

2.2.4 Climate

The climate at Camp SLO is considered Mediterranean, with a subtropical dry summer, abundant 

sunshine, and modest precipitation in winter. Camp SLO has seasonally warm summers and mild 

winters. The average temperature is 60.5 degrees Fahrenheit (°F), with summer highs of 77.9 °F 

and winter lows of 44 °F (National Oceanic and Atmospheric Administration [NOAA], 2022). 

Average annual precipitation is 22.42 inches.
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 2-5

2.2.5 Current and Future Land Use

Camp SLO serves as a year-round training facility for the CAARNG. The cantonment area of the 

facility is developed with numerous buildings and related infrastructure including paved and 

unpaved roadways and parking areas. The cantonment area occupies a small percentage of the 

total area controlled by the CAARNG, the other, much larger lands of which are occupied by and 

used as training ranges. The ranges are generally in vegetated sloping areas, mostly to the north 

of Highway 1. Access to lands under Camp SLO purview is restricted and inaccessible to the 

general public in most areas. 

The facility’s mission is to maintain and allocate training areas, airspace, facilities, and ranges in

order to support CAARNG. Additionally, the facility provides quality of life, logistical support to

training units, and administrative services. Tenants include CAL FIRE, CAL Trans, California

Conservation Corps, and California Specialized Training, Inc. There are no residential

areas/buildings in the AOIs. Future land use is not anticipated to change.

2.2.6 Sensitive Habitat and Threatened/ Endangered Species 

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

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

San Luis Obispo County, California (US Fish and Wildlife Service [USFWS], 2022). 

• Amphibians: California tiger Salamander, Ambystoma californiense (endangered); Arroyo

(=arroyo southwestern) toad, Anaxyrus californicus (endangered); California red-legged

frog, Rana draytonii (threatened)

• Birds: Short-tailed albatross, Phoebastria (=Diomedea) albatrus (endangered); No

Common Name, Coccyzus americanus ssp. occidentalis (species of concern); California

condor, Gymnogyps californianus (endangered); California clapper rail, Rallus longirostris

obsoletus (endangered); Southwestern willow flycatcher, Empidonax traillii extimus

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

least tern, Sterna antillarum browni (endangered); Marbled murrelet, Brachyramphus

marmoratus (threatened); Least Bell's vireo, Vireo bellii pusillus (endangered); Yellow-billed

Cuckoo, Coccyzus americanus (threatened)

• Crustaceans: Longhorn fairy shrimp, Branchinecta longiantenna (endangered);

Conservancy fairy shrimp, Branchinecta conservation (endangered); Vernal pool fairy

shrimp, Branchinecta lynchi (threatened)

• Fishes: Delta smelt, Hypomesus transpacificus (threatened); Tidewater goby,

Eucyclogobius newberryi (endangered)

• Flowering Plants: California jewelflower, Caulanthus californicus (endangered); California

seablite, Suaeda californica (endangered); Spreading navarretia, Navarretia fossalis

(threatened); Kern mallow, Eremalche kernensis (endangered); Morro manzanita,

Arctostaphylos morroensis (threatened); Gambel's watercress, Rorippa gambellii

(endangered); Salt marsh bird's-beak, Cordylanthus maritimus ssp. maritimus

(endangered); Indian Knob mountainbalm, Eriodictyon altissimum (endangered); La

Graciosa thistle, Cirsium loncholepis (endangered); Monterey spineflower, Chorizanthe

pungens var. pungens (threatened); Purple amole, Chlorogalum purpureum (threatened);

Pismo clarkia, Clarkia speciosa ssp. immaculata (endangered); Marsh Sandwort, Arenaria

paludicola (endangered); Chorro Creek bog thistle, Cirsium fontinale var. obispoense

(endangered); Nipomo Mesa lupine, Lupinus nipomensis (endangered); San Joaquin woolythreads, Monolopia (=Lembertia) congdonii (endangered); Gaviota Tarplant, Deinandra

increscens ssp. villosa (endangered)
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 2-6

• Insects: Monarch butterfly, Danaus plexippus (candidate); Kern primrose sphinx moth,

Euproserpinus Euterpe (threatened); Unsilvered fritillary, Speyeria adiaste (resolved taxon);

Smith's blue butterfly, Euphilotes enoptes smithi (endangered)

• Mammals: Little brown bat, Myotis lucifugus (under review); Southern sea otter, Enhydra

lutris nereis (threatened); Buena Vista Lake ornate Shrew, Sorex ornatus relictus

(endangered); Tipton kangaroo rat, Dipodomys nitratoides nitratoides (endangered); Giant

kangaroo rat, Dipodomys ingens (endangered); Swift fox, Vulpes velox (resolved taxon);

San Joaquin kit fox, Vulpes macrotis mutica (endangered); Morro Bay kangaroo rat,

Dipodomys heermanni morroensis (endangered)

• Reptiles: Leatherback sea turtle, Dermochelys coriacea (endangered); Blunt-nosed leopard

lizard, Gambelia silus (endangered); Olive ridley sea turtle, Lepidochelys olivacea

(threatened); Giant garter snake, Thamnophis gigas (threatened)

• Snails: Morro shoulderband (=Banded dune) snail, Helminthoglypta walkeriana

(threatened)

2.3 History of PFAS Use

Seven potential release areas were identified at Camp SLO during the PA where AFFF may have 

been used or released historically (AECOM, 2020). In 1972, an airplane crashed in Chorro Creek,

and it is possible that AFFF was used to extinguish any fires. AFFF may have been released at 

the facility during fire training activities between 1978 and 2007. In 2013, AFFF may have been 

released during the flushing of hoses and a tank that contained AFFF. Additionally, storage of 

AFFF may have resulted in incidental spills. 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, as screening values were established after SI planning and 

execution. However, ARNG will add HFPO-DA to the list of constituents sampled during the next 

phase of CERCLA if warranted. The potential release areas were grouped into six AOIs based on 

proximity to one another and groundwater flow. These AOIs are generally located in the western

portion of the facility. A description of each AOI is presented in Section 3. 
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Facility Location

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Facility Topography

Base Map: USGS The National Map: National

Boundaries Dataset, 3DEP Elevation Program,

0 2,000 4,000 8,000

Feet

Legend

Facility Boundary

AECOM 2-8
( (

( (

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Well No. 2

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Groundwater Features ­ Figure 2-3 12420 Milestone Center Drive

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Legend

Facility Boundary

Water Body

Pipeline

River/Stream

Groundwater Flow Direction

Geology

Q - Marine and nonmarine

(continental) sedimentary

rocks

Qls - Landslide deposits

(Holocene & Pleistocene)

M - Miocene marine rocks

Tv - Tertiary Volcanics

Ti - Morro Rock

Ku - Upper Cretaceous marine

rocks

Kl - Lower Cretaceous marine

rocks

KJf - Fanciscan Complex

Mzv - Undivided Mesozoic

volcanic and metavolcanic

rocks

um - Ultramafic Rocks

Contact, Certain

Fault, Approx.

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( Thrust Fault, Certain

Wells

A! Monitoring Wells

A! Unknown Wells

0 2,250 4,500 9,000

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AECOM 2-9
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SLO-01

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179.76

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191.93

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AOI04-01

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AOI06-01

DRY

Chorro Creek

Chorro Creek

Dairy Creek

Pennington Creek

180

200

190

190

200

180

0 250 500 1,000

Feet

­ Figure 2-4

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Groundwater Flow Direction

Groundwater Elevations, June 2021

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Groundwater elevations in ft NAVD88.

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Da iry

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Pennington

Cr eek

ChorroCreek

Upper San Luis Obispo

Creek Watershed

Lower San Luis Obispo

Creek Watershed

Los Osos Creek

Watershed

Chorro Creek

Watershed

0 1,000 2,000 4,000

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Direction

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AECOM 

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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, six AOIs were identified at Camp 

SLO and grouped, five of which were investigated during the SI (AECOM, 2020). AOI 5 was 

determined to be located outside of the facility boundaries and was, therefore, not sampled as 

part of the SI. The potential release areas are shown on Figure 3-1. 

3.1 AOI 1 Former Cal FIRE Training Area

AOI 1 is the former CAL FIRE Fire Training Area (FTA), now used by an outside contractor for a 

once-annual fire training session. Potential releases to soil by CAL FIRE occurred at AOI 1 during 

fire training activities from 1995/1996 to 2005/2006. Once a year, during these two timeframes, 

one 5-gallon container of 3% AFFF was reported to have been used to train firefighters on how to 

apply foam. The foam was directed at various props and a concrete cinder-block structure. AFFF 

was expelled from equipment nozzles during the training and released to the ground surface, 

which was observed in aerial photographs and during the PA site visit to be gravel covered.

3.2 AOI 2 Former META Yard Fire Training Area

AOI 2 is a parking lot area that was reportedly used for fire training. Potential releases to the east 

parking lot area of the Motorized Equipment Training Academy (META) yard occurred as early as 

1978 through 2007.

3.3 AOI 3 Cal FIRE Cuesta Camp Tenant

AOI 3 is located in the northeastern portion of Camp SLO, at a fueling facility associated with 

Cuesta Camp, which is operated by CAL FIRE; the fueling facility is near Building 621. Potential 

releases to concrete surfaces occurred in 2013 during the flushing out of hoses and a tank that 

contained AFFF. The precise location, amount, and type of AFFF released to the pavement and 

the condition of the pavement are not known.

PFAS-containing materials were reportedly released to a concrete surface and potentially 

migrated to the subsurface through cracks in the concrete or to areas off to the sides of concretecovered areas. 

3.4 AOI 4 O’Sullivan Airfield Shed

AOI 4 is a shed at the O’Sullivan Airfield and was observed during the PA site visit to contain two 

Tri-MaxTM crash carts that typically contain AFFF, three 5-gallon buckets of Chemguard 3% AFFF, 

and one 5-gallon bucket of FireAide 3% AFFF; the AFFF is stored on a concrete surface. Surface 

water and groundwater at and within the vicinity of the shed likely flows to the west/southwest, 

towards Chorro Creek. Although no incidental spills of stored AFFF were reported, AFFF could 

migrate to the subsurface through cracks in the concrete or to areas off to the sides of concrete 

covered areas. 

3.5 AOI 5 de Havilland Beaver Crash Site

In 1972, a de Havilland Beaver airplane belonging to the US Army crashed and came to rest in 

Chorro Creek. Interviewees did not recall whether AFFF were used to extinguish any fires. Note 

that this AOI is located outside of the facility boundaries and was, therefore, not sampled as part 

of the SI.
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Camp San Luis Obispo, San Luis Obispo, California

AECOM 3-2

3.6 AOI 6 Fuel Point

AOI 6 is located north of Chorro Creek and East of Dairy Creek, at a Fuel Point where a 5-gallon 

container of AFFF and an applicator were present during fueling operations. The AFFF material 

was reportedly transported to this site around 2011. The fuel point is situated on a concrete 

surface. If AFFF were released, it could migrate through cracks in the concrete surface or off the 

concreate to uncovered areas. 
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AOI 1

AOI 2

AOI 3

AOI 4

AOI 5

AOI 6

Dai ry

Creek

Penn ington Creek

Chorro Creek

Former CAL Chorro Creek

FIRE FTA

O'Sullivan Air

Field Shed

de Havilland

Beaver Crash Site

CAL FIRE Cuesta

Camp Tenant

Former META Yard

Fire Training Areas

Fuel

Point

Los Osos Creek

Watershed

Chorro Creek

Watershed

Well No. 2

Well No.3

Well No.1

0 425 850 1,700

Feet

­ Figure 3-1

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Area of Interest

Potential Release Area

Facility Boundary

Water Body

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Surface Water Flow Direction

Groundwater Flow Direction

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Areas of Interest

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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 Quality 

Assurance Project Plan (QAPP) Addendum (AECOM, 2021b), the objective of the SI is to identify 

whether there has been a release to the environment at the AOIs identified in the PA. For each 

AOI, ARNG determines if further investigation is warranted, a removal action is required to 

address immediate threats, or whether no further action is warranted. This SI evaluated 

groundwater and soil for presence or absence of relevant compounds at each of the sampled 

AOIs.

4.1 Problem Statement

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

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

SLs are presented in Section 6.1 of this report. 

4.2 Information Inputs

Primary information inputs included:

• The PA for Camp SLO (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, 2021b); and

• Field data collected during the SI, including groundwater elevations.

4.3 Study Boundaries

The scope of the SI was bounded by the property limits of the facility (Figure 2-2). Off-facility sampling 

was not included in the scope of this SI. If future off-facility sampling is required, the proper 

stakeholders will be notified, and necessary rights of entry will be obtained by ARNG with property 

owner(s). The SI scope was bounded vertically by the observed depths of the surficial groundwater 

table. Temporal boundaries were limited to the spring and fall, 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, 2021b). 

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, 2021b). 
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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, Camp San Luis Obispo, San Luis Obispo, California

dated January 2020 (AECOM, 2020);

• Final Site Safety and Health Plan, Camp San Luis Obispo, San Luis Obispo, California dated

May 2021 (AECOM, 2021a); and

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

Camp San Luis Obispo, San Luis Obispo, California dated June 2021 (AECOM, 2021b);

The SI field activities were conducted from 21 June to 25 June 2021 and 1 November to 5 November 

2021, which consisted of utility clearance, direct push boring, soil sample collection, temporary 

monitoring well installation and subsequent abandonment, grab groundwater sample collection, and 

land surveying. Field activities were conducted in accordance with the SI QAPP Addendum 

(AECOM, 2021b), 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-four (24) soil samples from 11 soil borings;

• Four grab groundwater samples from four temporary wells;

• Fifteen (15) 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. Field Change Request Forms are provided in Appendix B2, Nonconformance 

and Corrective Action Reports are provided in Appendix B3, and land survey data are provided 

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

5.1 Pre-Investigation Activities

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

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

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

5.1.1 Technical Project Planning

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

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

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

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

defining overall project objectives, including DQOs, and formulating a sampling approach to 

address the AOIs identified in the PA. 

A combined TPP Meeting 1 and 2 was held on 28 January 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, and RWQCB. 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, 2021b). 

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

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

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

5.1.2 Utility Clearance 

AECOM’s drilling subcontractor, Cascade Technical Services, LLC. placed a ticket with the USA 

DigAlert, the Northern California utility clearance provider to notify them of intrusive work on 16 

April 2021. 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 21 June 2021 with input from the AECOM field team and Camp 

SLO facility staff. General locating services and ground-penetrating radar were used to complete 

the clearance. Additionally, the first 5 feet of each boring were pre-cleared using a hand auger to 

verify utility clearance in shallow subsurface where utilities would typically be encountered. 

5.1.3 Source Water and Sampling Equipment Acceptability

A potable water source at Camp SLO was sampled prior to the field event, on 19 March 2021, to 

assess usability for decontamination of drilling equipment. Results of the sample collected at the 

wash rack spigot (SLO-PW-01) confirmed this source to be acceptable for use in this investigation; 

however, this location was inaccessible during the field event. As a result, an additional sample

(SLO-PW-02) was collected on 22 June 2021 from a hose bib at an alternate location. This 

alternate source was confirmed 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 samples associated 

with the water sources 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, 2021b). 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

During the first mobilization in June 2021, soil samples were collected via direct push technology 

(DPT), in accordance with the SI QAPP Addendum (AECOM, 2021b). A GeoProbe® 3126GT dualtube sampling system was used to collect continuous soil cores to the target depth. Due to rig 

refusal at two locations, a second mobilization was conducted in November 2021 using a sonic 

drill rig. During both mobilizations, a hand auger was used to collect soil from the top 5 feet of the 

boring, in accordance with AECOM utility clearance procedures. The soil boring locations are 

shown on Figure 5-1, and depths are provided Table 5-1. 
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, 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 

approximately 2 feet above the groundwater table, and one subsurface soil sample at the midpoint between the surface and the groundwater table. Soil samples collected from SLO-01 in June 

2021 were not analyzed because refusal was encountered and SLO-01 was scheduled to be 

completed during a second mobilization. During the November 2021 mobilization, SLO-01 could 

not be safely accessed with the sonic rig because recent rains had made the ground too soft. As 

a result, no soil or groundwater samples were collected from SLO-01. Additionally, groundwater 

was not encountered at boring locations AOI03-01, AOI04-01, and AOI06-01; however, soil 

samples were collected at these locations to evaluate presence or absence of the six PFAS 

compounds in soil. 

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 in a non-treated field logbook (i.e., composition 

notebook). Depth interval, recovery thickness, PID concentrations, moisture, relative density, 

color (using a Munsell soil color chart), and texture (using the USCS) were recorded. The boring 

logs are provided in Appendix E. 

Soil borings completed during the SI found silty sand and lean clay as the dominant lithology of 

the unconsolidated sediments below Camp SLO and are consistent with the alluvial and floodplain deposits described in the region. The borings were completed at depths between 30 and 

100 feet below ground surface (bgs). In the shallower portions of the borings, isolated layers of 

silt and gravel were also observed in the boring logs at thicknesses ranging from 0.5 to 9 feet. 

Many of the logs also reported varying percentages of gravel included in the sand packages. 

These results and facility observations are consistent with the understood localized use of fill 

material and the alluvial depositional environment. The original estimated depth to water was 

assumed to be 30 feet bgs, based on historical information. During the second mobilization, a 

maximum depth of 100 feet bgs was selected for drilling, given the lack of any moisture observed 

in the overburden and the challenging drilling conditions. These deeper borings were dominated 

by fine-grain materials (smectitic clay-dominated) consistent with the volcanic deposits in the 

region. 

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

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

and transported via Federal Express (FedEx) under standard chain of custody (CoC) procedures 

to the laboratory and analyzed by LC/MS/MS compliant with QSM 5.3 Table B-15, total organic 

carbon (TOC) (USEPA Method 9060A), and pH (USEPA Method 9045D) in accordance with the

SI QAPP Addendum (AECOM, 2021b).

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.

DPT borings were converted to temporary wells and were installed in grass areas to avoid 

disturbing concrete or asphalt surfaces where possible. No groundwater was encountered during 

the second mobilization using sonic drilling methods; thus, no wells were installed at that phase 

of work. 
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 5-4

5.3 Temporary Well Installation and Groundwater Grab Sampling

Temporary wells were installed using a GeoProbe® 3126GT dual-tube sampling system. Once 

the borehole was advanced to the desired depth, wherever conditions allowed, a temporary well 

was constructed of a 5-foot section of 1-inch Schedule 40 poly-vinyl chloride (PVC) screen with 

sufficient casing to reach ground surface. New PVC pipe and screen were used to avoid cross 

contamination between locations. The screen intervals for the temporary wells are provided in 

Table 5-2. 

Groundwater samples were collected after a period of time following well installation to allow 

groundwater to infiltrate and recharge the temporary well screen intervals. After the recharge 

period, groundwater samples were collected using a low-flow pump with PFAS-free HDPE tubing

and bladders. The temporary wells were purged at a rate determined in the field to reduce turbidity 

and draw down prior to sampling. 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, 2021b).

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.

Following well surveying (described below in Section 5.5), temporary wells were abandoned in 

accordance with the SI QAPP Addendum (AECOM, 2021b) by removing the PVC and backfilling 

the hole with bentonite chips. Upon completion of well abandonment, the ground surface at each 

location was patched to match existing surrounding conditions.

5.4 Synoptic Water Level Measurements

A synoptic groundwater gauging event was performed on 25 June 2021. Groundwater level 

measurements were collected from the four new temporary monitoring wells. Water level 

measurements were taken from the northern side of the well casing. Depth to water was 

measured in June 2021 from the newly installed wells that contained water. Only four of the seven 

wells installed contained water, and water levels ranged from 31.65 to 34.95 feet bgs. A 

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

in Table 5-2. 

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, 2021b). 

Survey data from the newly installed wells on the facility were collected on 25 June 2021 in the 

applicable Universal Transverse Mercator zone projection with World Geodetic System 84 datum 

(horizontal) and North American Vertical Datum 1988 (vertical). The surveyed well data are

provided in Appendix B4. 
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 5-5

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, 2021b) and with the DA Guidance for 

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

Soil IDW (i.e., soil cuttings) generated during the SI activities was containerized in properly

labeled 55-gallon drums. The IDW was stored at a location designated by CAARNG. ARNG will 

coordinate waste profiling, transportation, and disposal of the solid IDW. The soil IDW was not 

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

source location. 

Liquid IDW (i.e., purge water and decontamination fluids) generated during SI activities was 

containerized in properly labeled 55-gallon drums. The containerized IDW is being temporarily 

stored onsite, at a location designated by CAARNG. The liquid IDW will not be sampled and will 

assume the characteristics of the associated groundwater samples collected from the source 

locations. Based on laboratory results, containerized liquid IDW will be managed and disposed 

by ARNG (either by offsite disposal or onsite disposal with treatment, as appropriate) under a 

separate contract in accordance with SOP No. 042A for Treating Liquid Investigation-Derived 

Material (Purge water, drilling water, and decontamination fluids) (EA Engineering, Science, and 

Technology, Inc., 2021). ARNG will further coordinate in advance with the RWQCB to ensure 

proper disposal in accordance with state requirements and the Army Guidance for Addressing 

Releases of PFAS, Q18 (DA, 2018).

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

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

activities were disposed of at a licensed solid waste landfill.

5.7 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

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

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

(Appendix B2) and Nonconformance and Corrective Action Reports (Appendix B3): 

• During the June 2021 mobilization, the proposed location for temporary well SLO-01 was

located approximately 90 feet into dense, tall grasses. For both access and health and

safety reasons, the well location was moved approximately 80 feet to the northwest of the

originally proposed location to minimize the amount of required weed abatement required

to access the drilling location. This action was documented in a Field Change Request Form

in Appendix B2.

• During the June 2021 mobilization, the direct push drill rig was unable to drill to groundwater

due to a hard clay layer that was encountered at location SLO-01. During the November

2021 mobilization, recent rains made the ground too soft to allow the sonic drill rig to safely

access the location. Given that the field team was able to successfully sample the second

downgradient drilling location, SLO-02, and the inability of the drill rig to safely access the
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 5-6

location, drilling and sampling at SLO-01 were not completed. This action was documented 

in a Field Change Request Form in Appendix B2.

• During the November 2021 mobilization, the proposed drilling depth was up to 80 bgs and 

used sonic drilling to allow collection of groundwater samples from AOI 3, AOI 4, and AOI 

6. However, at approximately 27 feet bgs, the field team encountered completely dry clay 

that was difficult to drill through. This clay material was consistent to a depth of 100 feet bgs, 

20 feet below the planned total depth. Given the approximately 70 feet of dry clay 

encountered, migration to groundwater through this layer seems unlikely. Therefore, the 

boring was terminated at 100 feet bgs and a groundwater sample was not collected. This 

action was documented in a Field Change Request Form in Appendix B2. 

• Upon review of field documentation, it was discovered that well sampling forms were not 

completed, and field parameters were not collected during grab groundwater sampling. This 

action was documented in a nonconformance and corrective action report provided in 

Appendix B3.

• Upon review of field documentation and laboratory analytical data, it was discovered that 

the following QC samples were not collected as specified in the SI QAPP Addendum: 

groundwater field duplicate and groundwater MS/MSD. This action was documented in a 

nonconformance and corrective action report provided in Appendix B3.
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, Camp San Luis Obispo, 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)

Comments

AOI01-01-SB-00-02 6/22/2021 9:00 0 - 2 x x x

AOI01-01-SB-00-02D 6/22/2021 9:00 0 - 2 x FD

AOI01-01-SB-13-15 6/22/2021 9:50 13 - 15 x

AOI01-01-SB-36-38 6/22/2021 11:30 36 - 38 x

AOI01-02-SB-00-02 6/22/2021 12:10 0 - 2 x

AOI01-03-SB-00-02 6/22/2021 13:30 0 - 2 x

AOI02-01-SB-00-02 6/24/2021 8:00 0 - 2 x x x

AOI02-01-SB-00-02-MS 6/24/2021 8:00 0 - 2 x x MS

AOI02-01-SB-00-02-MSD 6/24/2021 8:00 0 - 2 x x MSD

AOI02-01-SB-13-15 6/24/2021 8:30 13 - 15 x

AOI02-01-SB-48-50 6/24/2021 9:45 48 - 50 x

AOI02-02-SB-00-02 6/24/2021 13:00 0 - 2 x

AOI02-02-SB-13-15 6/24/2021 13:30 13 - 15 x

AOI02-02-SB-41-43 6/24/2021 14:30 41 - 43 x

AOI03-01-SB-0-2 11/3/2021 15:40 0 - 2 x

AOI03-01-SB-00-02-D 11/3/2021 15:40 0 - 2 x FD

AOI03-01-SB-13-15 11/3/2021 16:20 13 - 15 x

AOI03-01-SB-79-80 11/4/2021 11:40 79 - 80 x

AOI03-02-SB-00-02 11/4/2021 13:00 0 - 2 x

AOI04-01-SB-00-02 11/4/2021 15:00 0 - 2 x x x

AOI04-01-SB-13-15 11/4/2021 15:20 13 - 15 x

AOI04-01-SB-79-80 11/5/2021 10:30 79 - 80 x

AOI06-01-SB-00-02 11/1/2021 10:25 0 - 2 x

AOI06-01-SB-13-15 11/1/2021 11:15 13 - 15 x

AOI06-01-SB-80-81 11/3/2021 8:45 80 - 81 x

SLO-02-SB-00-02 6/23/2021 8:30 0 - 2 x

SLO-02-SB-00-02D 6/23/2021 8:30 0 - 2 x FD

SLO-02-SB-13-15 6/23/2021 8:50 13 - 15 x

SLO-02-SB-35-37 6/23/2021 9:50 35 - 37 x

AOI01-01-GW 6/25/2021 9:00 NA x

AOI02-01-GW 6/25/2021 12:20 NA x

AOI02-02-GW 6/25/2021 13:30 NA x

SLO-02-GW 6/25/2021 11:05 NA x

Soil Samples

Groundwater Samples

AECOM 5-7
Table 5-1

Site Inspection Samples by Medium

Site Inspection Report, Camp San Luis Obispo, 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)

Comments

SLO-PW-01 3/19/2021 8:30 NA x Decon Source

SLO-PW-02 6/22/2021 7:30 NA x Decon Source

SLO-FRB-01 6/25/2021 11:30 NA x

SLO-FRB-02 11/5/2021 10:50 NA x

SLO-ERB-02 6/24/2021 12:45 NA x Drill Shoe

SLO-ERB-03 6/25/2021 7:15 NA x Hand Auger

SLO-ERB-03 11/1/2021 14:00 NA x Hand Auger

SLO-ERB-04 6/25/2021 7:20 NA x

Stainless-Steel 

Bowl

SLO-ERB-04 11/5/2021 10:45 NA x

Stainless-Steel 

Bowl

SLO-ERB-05 6/25/2021 13:00 NA x Pump

Notes:

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

MS/MSD = matrix spike/ matrix spike duplicate

PW = potable water

QSM = Quality Systems Manual

SB = soil boring

SLO = San Luis Obispo

TOC = total organic carbon

USEPA = United States Environmental Protection Agency

Quality Control Samples

AECOM 5-8
Table 5-2

Soil Boring Depths, Temporary Well Screen Intervals, and Groundwater Elevations

Site Inspection Report, Camp San Luis Obispo, California

Area of 

Interest

Boring 

Location

Soil Boring 

Depth 

(feet bgs)

Temporary Well 

Screen Interval 

(feet bgs)

Top of Casing 

Elevation 

(feet NAVD88)

Ground Surface 

Elevation 

(feet NAVD88)

Depth to 

Water

(feet btoc)

Dept

Wa

(feet 

AOI01-01 43 32.5 - 37.5 1 225.74 225.72 33.81 33

AOI01-02 2 NA NA NA NA N

AOI01-03 2 NA NA NA NA N

AOI02-01 57 50.41 - 55.41 1 238.85 239.05 34.75 34

AOI02-02 50 45 - 50 237.27 237.22 33.64 33

AOI03-01 80 NA NA NA NA N

AOI03-02 2 NA NA NA NA N

4 AOI04-01 80 NA NA NA NA N

6 AOI06-01 100 NA NA NA NA N

SLO-01 30 NA NA NA NA NSLO-02 43 37.5 - 42.5 1 213.90 211.41 34.14 31

Notes:

1 Temporary well screen set above total depth to capture groundwater interfaceAOI = area of interest

bgs = below ground surfacebtoc = below top of casingNA = not applicableNAVD88 = North American Vertical Datum 1988SLO = San Luis Obispo

21

Facility 

Boundary

3

AECOM 
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 5-10

THIS PAGE INTENTIONALLY BLANK
?!

?!

?!

"S

"S

?!

?!

?!

"S

?!

?!

Chorro Creek

Chorro Creek

Dairy Creek

Pen n ingtonCreek

SLO-01

SLO-02

AOI01-01

AOI01-02

AOI01-03

AOI02-01

AOI02-02

AOI03-01

AOI03-02

AOI04-01

AOI06-01

0 250 500 1,000

Feet

­ Figure 5-1

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Camp San Luis Obispo, CA

8/23/2022

8/23/2022

8/23/2022

MS

SL

CM

GIS BY

CHK BY

PM

Base Map: Sources: Esri, HERE, Garmin, USGS, Intermap, INCREMENT P, NRCan,

Esri Japan, METI, Esri China (Hong Kong), Esri Korea, Esri (Thailand), NGCC, (c)

8/23/2022

1:6,000

Legend

?! Soil Boring/Temporary Monitoring Well

"S Surface Soil Sampling

Facility Boundary

Water Body

Wetland

River/Stream

Surface Water Flow Direction

Groundwater Flow Direction

Site Inspection Sample Locations

12420 Milestone Center Drive

Germantown, MD 20876

AECOM 5-11
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 5-12

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Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, 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. 
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Camp San Luis Obispo, San Luis Obispo, California

AECOM 6-2

6.2 Soil Physicochemical Analyses

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

are important for evaluating transport through the soil medium. Appendix F contains the results 

of the TOC and pH 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: Former Cal FIRE Training Area. 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 and AOI01-

02. Soil was also sampled from shallow subsurface soil (13 to 15 feet bgs) and deep subsurface

soil (36 to 38 feet bgs) from boring location AOI01-01. 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 above the SL of 13 micrograms per kilogram (μg/kg) in surface soil at AOI01-

01, with a concentration of 71.9 μg/kg. PFOA, PFHxS, PFNA, and PFBS were detected below the 

SLs in surface soil, with the following maximum concentrations: PFOA at 5.76 μg/kg, PFHxS at 

12.7 μg/kg, PFNA at 13.6 μg/kg, and PFBS at 0.656 J μg/kg. 

PFOA, PFOS, PFHxS, PFBS, and PFNA were not detected in shallow subsurface soil. PFOA, 

PFOS, PFHxS, PFNA, and PFBS were detected in deep subsurface soil at AOI01-01, with the 

following concentrations: PFOA at 0.159 J μg/kg, PFOS at 0.401 J μg/kg, PFHxS at 0.376 J μg/kg, 

PFNA at 0.088 J μg/kg, and PFBS at 0.077 J μg/kg. 

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

bgs), and deep subsurface soil (35 to 37 feet bgs) from boring location SLO-02, downgradient of 

AOI 1 and near the facility boundary. PFOA, PFOS, PFHxS, PFNA, and PFBS were not detected 

in any soil interval at SLO-02. 

6.3.2 AOI 1 Groundwater Analytical Results 

Groundwater was sampled from temporary monitoring well AOI01-01. Figure 6-6 and Figure 6-

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

results. 
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 6-3

The following detections were measured with regards to the SLs:

• PFOA was detected above the SL of 6 nanograms per liter (ng/L), at a concentration of

291 ng/L.

• PFOS was detected above the SL of 4 ng/L, at a concentration of 182 ng/L.

• PFHxS was detected above the SL of 39 ng/L, at a concentration of 908 ng/L.

• PFNA was detected above the SL of 6 ng/L, at a concentration of 69.9 ng/L.

• PFBS was detected below the SL of 601 ng/L, at a concentration of 427 ng/L.

Groundwater was also sampled from temporary monitoring well SLO-02, downgradient of AOI 1

and near the facility boundary. PFOA, PFOS, and PFBS were detected below their respective 

SLs, with concentrations of 2.27 J ng/L, 2.67 J ng/L, and 1.20 J ng/L, respectively. PFHxS and 

PFNA were not detected in groundwater at SLO-02. 

6.3.3 AOI 1 Conclusions

Based on the results of the SI, PFOS was detected in surface soil at a concentration above the 

SL. PFOA, PFOS, PFHxS, and PFNA were detected in groundwater above their SLs. Based on 

the exceedances of the SLs in soil and groundwater, further evaluation at AOI 1 is warranted. 

6.4 AOI 2 

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

AOI 2: Former META Yard Fire Training Area. The results in soil and groundwater are summarized 

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

through Figure 6-7. 

6.4.1 AOI 2 Soil Analytical Results

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

and deep subsurface soil (48 to 50 feet bgs and 41 to 43 feet bgs) from boring locations AOI02-

01 and AOI02-02. 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 at location AOI02-01, with a concentration of 

0.110 J μg/kg. PFOA, PFHxS, PFNA, and PFBS were not detected in surface soil. PFOA, PFOS, 

PFHxS, PFNA, and PFBS were not detected in shallow and deep subsurface soil. 

6.4.2 AOI 2 Groundwater Analytical Results 

Groundwater was sampled from temporary monitoring wells AOI02-01 and AOI02-02. Figure 6-6

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

groundwater results. 

PFOS was detected above the SL of 4 ng/L at AOI 02-01, at a concentration of 6.12 ng/L. PFOS 

was detected below the SL at AOI02-02, with a concentration of 1.09 J. PFOA, PFHxS, PFNA, 

and PFBS were detected below their SLs in groundwater at both locations, with the following 

maximum concentrations: PFOA at 5.15 ng/L, PFHxS at 4.37 ng/L, and PFBS at 1.07 J ng/L. 

PFNA was not detected in groundwater at either location. 
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 6-4

6.4.3 AOI 2 Conclusions

Based on the results of the SI, PFOS was detected in soil at a concentration below the SL. PFOS 

was detected at a concentration above the SL in groundwater. Based on the exceedance of the 

SL in groundwater, further evaluation at AOI 2 is warranted.

6.5 AOI 3

This section presents the analytical results for soil in comparison to SLs for AOI 3: Cal FIRE 

Cuesta Camp Tenant. The results in soil are presented in Table 6-2 through Table 6-4. Soil results 

are presented on Figure 6-1 through Figure 6-5. Groundwater was not encountered during field 

activities at AOI 3.

6.5.1 AOI 3 Soil Analytical Results

Soil was sampled from surface soil (0 to 2 feet bgs) from boring locations AOI03-01 and AOI03-

02. Soil was also sampled from shallow subsurface soil (13 to 15 feet bgs) and deep subsurface 

soil (79 to 80 feet bgs) from boring location AOI3-01. PFOS, PFHxS, and PFBS were detected 

below the SLs in surface soil, at maximum concentrations of 0.999 J μg/kg, 0.050 J μg/kg, and 

0.075 J μg/kg, respectively. PFOA and PFNA were not detected in surface soil. PFOA, PFOS, 

PFHxS, PFNA, and PFBS were not detected in shallow and deep subsurface soil. 

6.5.2 AOI 3 Conclusions

Based on the results of the SI, PFOS, PFHxS, and PFBS were detected in soil below their SLs. 

Therefore, further evaluation is not warranted at AOI 3. 

6.6 AOI 4

This section presents the analytical results for soil in comparison to SLs for AOI 4: O’Sullivan 

Airfield Shed. The results in soil are presented in Table 6-2 through Table 6-4. Soil results are 

presented on Figure 6-1 through Figure 6-5. Groundwater was not encountered during field 

activities at AOI 4.

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 (79 to 80 feet bgs) from boring location AOI04-01. PFOA, PFOS, 

PFHxS, PFNA, and PFBS were not detected in surface, shallow subsurface, and deep subsurface 

soil.

6.6.2 AOI 4 Conclusions

Based on the results of the SI, PFOA, PFOS, PFHxS, PFNA, and PFBS were not detected in soil. 

Therefore, further evaluation is not warranted at AOI 4.

6.7 AOI 6

This section presents the analytical results for soil in comparison to SLs for AOI 6: Fuel Point. The 

results in soil are presented in Table 6-2 through Table 6-4. Soil results are presented on Figure 

6-1 through Figure 6-5. Groundwater was not encountered during field activities at AOI 6.
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 6-5

6.7.1 AOI 6 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 (80 to 81 feet bgs) from boring location AOI06-01. PFOA and PFOS 

were detected below their SLs in surface soil, with concentrations of 0.102 J μg/kg and 0.292 J 

μg/kg, respectively. PFHxS, PFNA, and PFBS were not detected in surface soil. PFOA, PFOS, 

PFHxS, PFNA, and PFBS were not detected in shallow and deep subsurface soil. 

6.7.2 AOI 6 Conclusions 

Based on the results of the SI, PFOS and PFBS were detected in soil below their SLs. Therefore, 

further evaluation is not warranted at AOI 6. 
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 6-6

THIS PAGE INTENTIONALLY BLANK
Table 6-2

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

Site Inspection Report, Camp San Luis Obispo

Analyte OSD Screening 

Level a

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

PFBS 1900 0.189 J 0.345 J 0.656 J ND U ND U ND UJ 0.075 J ND U ND U ND UPFHxS 130 7.26 12.7 1.52 ND U ND U ND UJ 0.049 J 0.050 J ND U ND U

PFNA 19 7.60 13.6 ND U ND U ND U ND U ND U ND U ND U ND UPFOA 19 3.69 J 5.76 0.602 J ND U ND U ND U ND U ND U ND U 0.102 J

PFOS 13 71.9 J 41.0 J ND U 0.110 J ND U ND UJ 0.999 J 0.177 J ND U 0.292 J

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acidPFOA perfluorooctanoic acidPFOS perfluorooctanesulfonic acidAcronyms and Abbreviations

AOI Area of InterestD duplicate

DL detection limit

ft feetHQ hazard quotientID identificationLCMSMS liquid chromatography with tandem mass spectrometryLOD limit of detectionND analyte not detected above the LODOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierSLO San Luis ObispoSB soil boringUSEPA United States Environmental Protection Agencyμg/kg micrograms per kilogram

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

Interpreted Qualifiers

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

AOI01 AOI02 AOI03 AOI06

AOI06-01-SB-00-02

11/01/2021

0-2 ft

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

AOI03-02-SB-00-02

11/04/2021

0-2 ft

AOI04

AOI04-01-SB-00-02

11/04/2021

0-2 ft

AOI03-01-SB-00-02

11/03/2021

0-2 ft

AOI03-01-SB-00-02-D

11/03/2021

0-2 ft

AOI02-01-SB-00-02

06/24/2021

0-2 ft

AOI02-02-SB-00-02

06/24/2021

0-2 ft

AOI01-01-SB-00-02D

06/22/2021

0-2 ft

AOI01-02-SB-00-02

06/22/2021

0-2 ft

Area of Interest

Sample ID

Sample Date

Depth

AOI01-01-SB-00-02

06/22/2021

0-2 ft

AECOM 
Table 6-2

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

Site Inspection Report, Camp San Luis Obispo

Analyte OSD Screening 

Level a

Result Qual Result Qual

PFBS 1900 ND U ND UPFHxS 130 ND U ND UPFNA 19 ND U ND UPFOA 19 ND U ND UPFOS 13 ND U ND U

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acidPFOA perfluorooctanoic acidPFOS perfluorooctanesulfonic acidAcronyms and Abbreviations

AOI Area of InterestD duplicate

DL detection limit

ft feetHQ hazard quotientID identificationLCMSMS liquid chromatography with tandem mass spectrometryLOD limit of detectionND analyte not detected above the LODOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierSLO San Luis ObispoSB soil boringUSEPA United States Environmental Protection Agencyμg/kg micrograms per kilogram

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

Interpreted Qualifiers

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

SLO-02

SLO-02-SB-00-02D

06/23/2021

0-2 ft

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

Area of Interest

Sample ID

Sample Date

Depth

SLO-02-SB-00-02

06/23/2021

0-2 ft

AECOM 
Table 6-3

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

Site Inspection Report, Camp San Luis Obispo

Analyte OSD Screening 

Level a

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

PFBS 25000 ND U ND U ND U ND U ND U ND U ND UPFHxS 1600 ND U ND U ND U ND U ND U ND U ND UPFNA 250 ND U ND U ND U ND U ND U ND U ND UPFOA 250 ND U ND U ND U ND U ND U ND U ND UPFOS 160 ND U ND U ND U ND U ND U ND U ND U

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acid

References PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acidPFOA perfluorooctanoic acidPFOS perfluorooctanesulfonic acid

Interpreted Qualifiers Acronyms and Abbreviations

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

D duplicateDL detection limitft feetHQ hazard quotientID identificationLCMSMS liquid chromatography with tandem mass spectrometryLOD limit of detectionND analyte not detected above the LODOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierSLO San Luis ObispoSB soil boringUSEPA United States Environmental Protection Agencyμg/kg micrograms per kilogram

Area of Interest

Sample ID

Sample Date

Depth

AOI01

AOI01-01-SB-13-15

06/22/2021

13-15 ft

AOI04-01-SB-13-15

11/04/2021

13-15 ft

AOI02-01-SB-13-15

06/24/2021

13-15 ft

AOI02-02-SB-13-15

06/24/2021

13-15 ft

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

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

AOI02 AOI06

AOI06-01-SB-13-15

11/01/2021

13-15 ft

SLO-02

SLO-02-SB-13-15

06/23/2021

13-15 ft

AOI03

AOI03-01-SB-13-15

11/03/2021

13-15 ft

AOI04

AECOM 
Table 6-4

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

Site Inspection Report, Camp San Luis Obispo

Area of Interest

Sample ID

Sample Date

Depth

Analyte Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual Result Qual

PFBS 0.077 J ND U ND U ND U ND U ND U ND UPFHxS 0.376 J ND U ND U ND U ND U ND U ND UPFNA 0.088 J ND U ND U ND U ND U ND U ND UPFOA 0.159 J ND U ND U ND U ND U ND U ND UPFOS 0.401 J ND U ND U ND U ND U ND U ND U

Interpreted Qualifiers Chemical AbbreviationsJ = Estimated concentration PFBS perfluorobutanesulfonic acidU = The analyte was not detected at a level greater than or equal to the adjusted DL PFHxS perfluorohexanesulfonic acid

PFNA perfluorononanoic acidPFOA perfluorooctanoic acidPFOS perfluorooctanesulfonic acidAcronyms and Abbreviations

AOI Area of InterestD duplicateDL detection limitft feetID identificationLCMSMS liquid chromatography with tandem mass spectrometryLOD limit of detectionND analyte not detected above the LODQSM Quality Systems ManualQual interpreted qualifierSLO San Luis ObispoSB soil boringμg/kg micrograms per kilogram

AOI01

AOI01-01-SB-36-38

06/22/2021

36-38 ft

AOI02-01-SB-48-50

06/24/2021

48-50 ft 41-43 ft

AOI03

AOI03-01-SB-79-80

11/04/2021

79-80 ft

SLO-02

SLO-02-SB-35-37

06/23/2021

35-37 ft

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

AOI02 AOI04

AOI04-01-SB-79-80

11/05/2021

79-80 ft

AOI06

AOI06-01-SB-80-81

11/03/2021

80-81 ft

AOI02-02-SB-41-43

06/24/2021

AECOM 
Table 6-5

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

Site Inspection Report, Camp San Luis Obispo

Analyte OSD Screening 

Level a

Result Qual Result Qual Result Qual Result Qual

PFBS 601 427 1.07 J 0.823 J 1.20 JPFHxS 39 908 4.37 2.00 J ND U

PFNA 6 69.9 ND U ND U ND UPFOA 6 291 5.15 0.840 J 2.27 JPFOS 4 182 6.12 1.09 J 2.67 J

Grey Fill Detected concentration exceeded OSD Screening Levels Chemical Abbreviations

PFBS perfluorobutanesulfonic acidPFHxS perfluorohexanesulfonic acidPFNA perfluorononanoic acidPFOA perfluorooctanoic acidPFOS perfluorooctanesulfonic acidAcronyms and Abbreviations

AOI Area of InterestD duplicateDL detection limitGW groundwaterHQ hazard quotientID identificationLCMSMS liquid chromatography with tandem mass spectrometryLOD limit of detectionND analyte not detected above the LODOSD Office of the Secretary of DefenseQSM Quality Systems ManualQual interpreted qualifierSLO San Luis ObispoUSEPA United States Environmental Protection Agencyng/l nanogram per liter

SLO-02

SLO-02-GW

06/25/2021

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

References

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 incidental ingestion of groundwater.

Interpreted Qualifiers

J = Estimated concentrationU = The analyte was not detected at a level greater than or equal to the adjusted DL

AOI02

AOI02-01-GW

06/25/2021

AOI02-02-GW

06/25/2021

Area of Interest

Sample ID

Sample Date

AOI01

AOI01-01-GW

06/25/2021

AECOM 
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 6-12

THIS PAGE INTENTIONALLY BLANK
Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI01-02

AOI02-01 AOI02-02

AOI03-01

AOI03-02

AOI04-01

AOI06-01

Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI02-01 AOI02-02

AOI03-01

AOI04-01

AOI06-01

Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI02-01 AOI02-02

AOI03-01

AOI04-01

AOI06-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-1

PFOA Detections in Soil

8/23/2022

8/23/2022

MS 8/23/2022

SL

CM

GIS BY

CHK BY

PM

8/23/2022

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Camp San Luis Obispo, CA

Base Map: Source: Esri, Maxar, Earthstar Geographics, and

the GIS User Community

1:12,000

Shallow

Intermediate

Deep

0 500 1,000 2,000

­

Feet

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

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

Facility Boundary

Water Body

Wetland

River/Stream

PFOA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

AECOM 6-13
Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI01-02

AOI02-01 AOI02-02

AOI03-01 AOI03-02

AOI04-01

AOI06-01

Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI02-01 AOI02-02

AOI03-01

AOI04-01

AOI06-01

Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI02-01 AOI02-02

AOI03-01

AOI04-01

AOI06-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-2

PFOS Detections in Soil

8/23/2022

8/23/2022

MS 8/23/2022

SL

CM

GIS BY

CHK BY

PM

8/23/2022

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Camp San Luis Obispo, CA

Base Map: Source: Esri, Maxar, Earthstar Geographics, and

the GIS User Community

1:12,000

Shallow

Intermediate

Deep

0 500 1,000 2,000

­

Feet

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

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

Facility Boundary

Water Body

Wetland

River/Stream

PFOS Results (μg/Kg)

ND

>ND - 13

>13 - 160

>160 - 1,600

>1,600

AECOM 6-14
Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI01-02

AOI02-01 AOI02-02

AOI03-01

AOI03-02

AOI04-01

AOI06-01

Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI02-01 AOI02-02

AOI03-01

AOI04-01

AOI06-01

Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI02-01 AOI02-02

AOI03-01

AOI04-01

AOI06-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-3

PFBS Detections in Soil

8/23/2022

8/23/2022

MS 8/23/2022

SL

CM

GIS BY

CHK BY

PM

8/23/2022

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Camp San Luis Obispo, CA

Base Map: Source: Esri, Maxar, Earthstar Geographics, and

the GIS User Community

1:12,000

Shallow

Intermediate

Deep

0 500 1,000 2,000

­

Feet

Facility Boundary

Water Body

Wetland

River/Stream

PFBS Results (μg/Kg)

ND

>ND - 10

>10 - 1,900

>1,900 - 25,000

>25,000

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

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

AECOM 6-15
Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI01-02

AOI02-01 AOI02-02

AOI03-01 AOI03-02

AOI04-01

AOI06-01

Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI02-01 AOI02-02

AOI03-01

AOI04-01

AOI06-01

Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI02-01 AOI02-02

AOI03-01

AOI04-01

AOI06-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-4

PFHxS Detections in Soil

8/23/2022

8/23/2022

MS 8/23/2022

SL

CM

GIS BY

CHK BY

PM

8/23/2022

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Camp San Luis Obispo, CA

Base Map: Source: Esri, Maxar, Earthstar Geographics, and

the GIS User Community

1:12,000

Shallow

Intermediate

Deep

0 500 1,000 2,000

­

Feet

Facility Boundary

Water Body

Wetland

River/Stream

PFHxS Results (μg/Kg)

ND

>ND - 10

>10 - 130

>130 - 1,600

>1,600

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

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

AECOM 6-16
Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI01-02

AOI02-01 AOI02-02

AOI03-01

AOI03-02

AOI04-01

AOI06-01

Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI02-01 AOI02-02

AOI03-01

AOI04-01

AOI06-01

Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI02-01 AOI02-02

AOI03-01

AOI04-01

AOI06-01

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-5

PFNA Detections in Soil

8/23/2022

8/23/2022

MS 8/23/2022

SL

CM

GIS BY

CHK BY

PM

8/23/2022

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Camp San Luis Obispo, CA

Base Map: Source: Esri, Maxar, Earthstar Geographics, and

the GIS User Community

1:12,000

Shallow

Intermediate

Deep

Facility Boundary

Water Body

Wetland

River/Stream

0 500 1,000 2,000

­

Feet

PFNA Results (μg/Kg)

ND

>ND - 19

>19 - 250

>250 - 2,500

>2,500

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

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

AECOM 6-17
Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI02-01 AOI02-02

Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI02-01 AOI02-02

Chorro Creek

Chorro Creek

Pe nnington Creek

Dairy Creek

SLO-02

AOI01-01

AOI02-01 AOI02-02

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-6

PFOA, PFOS, and PFBS Detections 

in Groundwater

10/5/2022

10/5/2022

MS 10/5/2022

SL

CM

GIS BY

CHK BY

PM

10/5/2022

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Camp San Luis Obispo, CA

Base Map: Source: Esri, Maxar, Earthstar Geographics, and

the GIS User Community

1:12,000

PFOA

PFOS

PFBS

Facility Boundary

Water Body

Wetland

River/Stream

Groundwater Flow Direction

PFOA Results (ng/L)

ND

>ND - 6

>6 - 40

>40 - 70

>70

0 500 1,000 2,000

­

Feet

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

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

AECOM 6-18
Chorro Creek

Chorro Creek

Pen n ingto n Creek

Dairy Creek

SLO-02

AOI01-01

AOI02-01 AOI02-02

Chorro Creek

Chorro Creek

Pen n ingto n Creek

Dairy Creek

SLO-02

AOI01-01

AOI02-01 AOI02-02

12420 Milestone Center Drive

Germantown, MD 20876 Figure 6-7

PFHxS and PFNA Detections 

in Groundwater

8/23/2022

8/23/2022

MS 8/23/2022

SL

CM

GIS BY

CHK BY

PM

8/23/2022

CLIENT

REVISED

SCALE

PROJECT

ARNG

Site Inspection at Camp San Luis Obispo, CA

Base Map: Source: Esri, Maxar, Earthstar Geographics, and

the GIS User Community

1:12,000

PFHxS

PFNA

Facility Boundary

Water Body

Wetland

River/Stream

Groundwater Flow Direction

PFHxS Results (ng/L)

ND

>ND - 39

>39 - 100

>100 - 1,000

>1,000

0 500 1,000 2,000

­

Feet

PFNA Results (ng/L)

ND

>ND - 6

>6 - 100

>100 - 1,000

>1,000

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

AECOM 6-19
THIS PAGE INTENTIONALLY BLANK

Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 7-1

7. Exposure Pathways

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

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

be impacted, the decision to move from SI to Remedial Investigation (RI) or interim action is 

determined based upon exceedances of the SLs for the relevant compounds and whether the 

release is more than likely attributable to the DoD. A CSM presents the current understanding of 

the site conditions with respect to known and suspected sources, potential transport mechanisms 

and migration pathways, and potentially exposed human receptors. A human exposure pathway 

is considered potentially complete when the following conditions are present:

1. Contaminant source;

2. Environmental fate and transport;

3. Exposure point;

4. Exposure route; and

5. Potentially exposed populations.

If any of these elements are missing, the pathway is incomplete. The CSM figures use an empty 

circle symbol to represent an incomplete exposure pathway. Areas with an incomplete pathway 

generally warrant no further action. However, the pathway is considered potentially complete if the 

relevant compounds are detected, in which case the CSM figure uses a half-filled circle symbol to 

represent a potentially complete exposure pathway. Additionally, a completely filled circle symbol is 

used to indicate when a potentially complete exposure pathway has detections of relevant 

compounds above the SLs. Areas with an identified potentially complete pathway that have 

detections of the relevant compounds above the SLs may warrant further investigation. Although 

the CSMs indicate whether potentially complete exposure pathways may exist, the 

recommendation for future study in an RI or no action at this time is based on the comparison of 

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

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

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

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

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

evaluated are consistent with those listed in USEPA guidance for risk screening (USEPA, 2001). 

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

workers, trespassers, residents outside the facility boundary, and recreational users outside of 

the facility boundary. 

7.1 Soil Exposure Pathway

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

between the source and potential receptors at AOI 1, AOI 2, AOI 3, AOI 4, and AOI 6 based on 

the aforementioned criteria. 

7.1.1 AOI 1 

Between 1995 and 2006, AFFF may have been released at AOI 1 during fire training activities

where AFFF was used to train firefighters on how to apply foam. PFOA, PFOS, PFHxS, PFNA

and PFBS were detected in surface soil at AOI 1, and PFOS exceeded the SL. Site workers and 

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

inhalation of dust. Therefore, the surface soil exposure pathway for site workers and future
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 7-2

construction workers are potentially complete. The pathways for current construction workers are 

considered incomplete because no active construction was observed at the facility during the time 

of SI field work. 

PFOA, PFOS, PFHxS, PFNA, and PFBS were detected in deep subsurface soil collected from 36 

to 38 feet bgs feet bgs. Construction workers are not reasonably expected to encounter soil 

greater than 15 feet bgs; therefore, the exposure pathway for subsurface soil is considered 

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

7.1.2 AOI 2 

As early as 1978 through 2007, AFFF may have been released at AOI 2 during fire training 

activities. PFOS was detected below the SL in surface soil at AOI 2. Site workers and construction 

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

Therefore, the surface soil exposure pathway for site workers and future construction workers are 

potentially complete. PFOA, PFOS, PFHxS, PFNA, and PFBS were not detected in subsurface 

soil at AOI 2; therefore, all exposure pathways are considered incomplete. The CSM for AOI 2 is 

presented on Figure 7-2. 

7.1.3 AOI 3 

In 2013, AFFF was potentially released to concrete surfaces at AOI 3 during the flushing out of 

hoses and a tank that contained AFFF. PFOS, PFHxS, and PFBS were detected below their SLs 

in surface soil at AOI 3. Site workers and construction workers could contact constituents in 

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

pathway for site workers and future construction workers are potentially complete. PFOA, PFOS, 

PFHxS, PFNA, and PFBS were not detected in subsurface soil at AOI 3; therefore, all exposure 

pathways are considered incomplete. The CSM for AOI 3 is presented on Figure 7-3. 

7.1.4 AOI 4 

AFFF may have potentially been released to soil at AOI 4 due to incidental spills related to AFFF 

storage at the O’Sullivan Airfield Shed. PFOA, PFOS, PFHxS, PFNA, and PFBS were not 

detected in surface or subsurface soil at AOI 4; therefore, the soil exposure pathways are 

incomplete. The CSM for AOI 4 is presented on Figure 7-4. 

7.1.5 AOI 6 

AFFF may have potentially been released at AOI 6 due to incidental spills related to AFFF storage 

at the Fuel Point. PFOA and PFOS were detected below their SLs in surface soil at AOI 6. Site

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

ingestion and inhalation of dust. Therefore, the surface soil exposure pathway for site workers 

and future construction workers are potentially complete. PFOA, PFOS, PFHxS, PFNA, and 

PFBS were not detected in subsurface soil; therefore, the subsurface soil exposure pathway for 

all receptors is considered incomplete. The CSM for AOI 6 is presented on Figure 7-3. 

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.
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 7-3

7.2.1 AOI 1 

PFOA, PFOS, PFHxS, and PFNA in groundwater exceeded their SLs in one temporary monitoring 

well at AOI 1. Depth to water measured at this well in June 2021 during the SI was 33.79 feet bgs. 

Therefore, groundwater is unlikely to be encountered during construction activities, and the 

ingestion exposure pathway for construction workers is considered incomplete. Camp SLO 

drinking water is sourced from a location upgradient of the facility. As such, the exposure pathway 

for site worker ingestion of groundwater is considered incomplete. Downgradient potable wells 

supply water to the City of Morro Bay, which is about 4 miles downgradient of the facility. There 

could also be private wells associated with farming operations downgradient of the facility and 

positioned between the facility and the City of Morro Bay. Conservatively, these wells could be a 

potentially complete pathway in groundwater. Therefore, the ingestion exposure pathway for 

groundwater is potentially complete for off-facility residents. The CSM for AOI 1 is presented on 

Figure 7-1. 

7.2.2 AOI 2 

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

the SL. Depth to water measured at these wells in June 2021 during the SI ranged from 33.59 to 

34.95 feet bgs. Therefore, groundwater is unlikely to be encountered during construction activities 

and the ingestion exposure pathway for construction workers is considered incomplete. As 

discussed in Section 7.2.1 above, the ingestion exposure pathway for groundwater is considered 

potentially complete for off-facility residents but incomplete for site workers. The CSM for AOI 2

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, AOI 2, AOI 3, and AOI 6 

PFAS are water soluble and can migrate readily from soil to surface water via leaching and runoff. Because PFOA, PFOS, PFHxS, PFNA, and PFBS were detected in soil and/or groundwater 

at the AOIs, it is possible that those compounds may have migrated from soil and groundwater to 

Chorro Creek. Therefore, the surface water and sediment ingestion exposure pathways for site 

workers and future construction workers are considered potentially complete. Chorro Creek and 

its tributaries converge with the Morrow Bay Estuary downstream of the facility. Therefore, the 

surface water and sediment ingestion exposure pathway for the off-facility recreational user is 

considered potentially complete. The CSMs for each AOI are presented on Figure 7-1 through 

Figure 7-3. 

7.3.2 AOI 4 

PFOA, PFOS, PFHxS, PFNA, and PFBS were not detected in soil at AOI 4. Therefore, the surface 

water and sediment ingestion exposure pathway are considered incomplete for all receptors. The 

CSM for AOI 4 is presented on Figure 7-4. 
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 7-4

THIS PAGE INTENTIONALLY BLANK
Media

SOURCE PATHWAY RECEPTOR

AOI 1 Fire Training

Human 

Activities

Precipitation/ 

Run-Off

Leaching/ 

Infiltration

Airborne Soil 

particulate

Surface Soil 

Surface 

Water/ 

sediment

Subsurface 

Soil

Shallow 

Groundwater

Source Release 

Mechanism Media Transport and Migration Media Exposure Routes

Inhalation of 

Dust

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

/ / / /

/ / / /

LEGEND

/ / / /

/ / /

/ / / /

Figure 7-1

Conceptual Site Model, AOI 1

Camp San Luis Obispo

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

Surface Soil

Surface 

Water Flow

NOTES

1. The resident and recreational users

refer to off-site receptors.

2. Inhalation of dust for off-site receptors

is likely insignificant.

3. No current active construction at the

facility.

Site Worker Construction Worker3 Resident1,2 Recreational User1,2

Site Worker Construction Worker3 Resident1,2 Recreational User1,2

/

AECOM 7-5
Media

SOURCE PATHWAY RECEPTOR

AOI 2 Fire Training

Human 

Activities

Precipitation/ 

Run-Off

Leaching/ 

Infiltration

Airborne Soil 

particulate

Surface Soil 

Surface 

Water/ 

sediment

Subsurface 

Soil

Shallow 

Groundwater

Source Release 

Mechanism Media Transport and Migration Media Exposure Routes

Inhalation of 

Dust

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

/ / / /

/ / / /

LEGEND

/ / / /

/ / /

/ / / /

Figure 7-2

Conceptual Site Model, AOI 2

Camp San Luis Obispo

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

Surface Soil

Surface 

Water Flow

NOTES

1. The resident and recreational users

refer to off-site receptors.

2. Inhalation of dust for off-site receptors

is likely insignificant.

3. No current active construction at the

facility.

Site Worker Construction Worker3 Resident1,2 Recreational User1,2

Site Worker Construction Worker3 Resident1,2 Recreational User1,2

/

AECOM 7-6
Media

SOURCE PATHWAY RECEPTOR

AOI 3

AOI 6

Incidental 

Spills

Human 

Activities

Precipitation/ 

Run-Off

Leaching/ 

Infiltration

Airborne Soil 

particulate

Surface Soil 

Surface 

Water/ 

sediment

Subsurface 

Soil

Shallow 

Groundwater

Source Release 

Mechanism Media Transport and Migration Media Exposure Routes

Inhalation of 

Dust

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

/ / / /

/ / / /

LEGEND

/ / / /

/ / /

/ / / /

Figure 7-3

Conceptual Site Model, AOI 3 and AOI 6

Camp San Luis Obispo

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

Surface Soil

Surface 

Water Flow

NOTES

1. The resident and recreational users

refer to off-site receptors.

2. Inhalation of dust for off-site receptors

is likely insignificant.

3. No current active construction at the

facility.

Site Worker Construction Worker3 Resident1,2 Recreational User1,2

Site Worker Construction Worker3 Resident1,2 Recreational User1,2

/

AECOM 7-7
Media

SOURCE PATHWAY RECEPTOR

AOI 4 Incidental 

Spills

Human 

Activities

Precipitation/ 

Run-Off

Leaching/ 

Infiltration

Airborne Soil 

particulate

Surface Soil 

Surface 

Water/ 

sediment

Subsurface 

Soil

Shallow 

Groundwater

Source Release 

Mechanism Media Transport and Migration Media Exposure Routes

Inhalation of 

Dust

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

/ / / /

/ / / /

LEGEND

/ / / /

/ / /

/ / / /

Figure 7-4

Conceptual Site Model, AOI 4

Camp San Luis Obispo

Potential 

Off-Facility 

Source Not 

under 

Control of 

ARNG

Surface Soil

Surface 

Water Flow

NOTES

1. The resident and recreational users

refer to off-site receptors.

2. Inhalation of dust for off-site receptors

is likely insignificant.

3. No current active construction at the

facility.

Site Worker Construction Worker3 Resident1,2 Recreational User1,2

Site Worker Construction Worker3 Resident1,2 Recreational User1,2

/

AECOM 7-8
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, 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 21 June to 25 June 2021 and 1 November to 5 November 

2021, which consisted of utility clearance, direct push boring, and sonic boring soil sample 

collection, temporary monitoring well installation and subsequent abandonment, grab groundwater 

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

QAPP Addendum (AECOM, 2021b), except as previously noted in Section 5.8. 

To fulfill the project DQOs set forth in the approved SI QAPP Addendum (AECOM, 2021b), 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-four (24) soil samples from 11 soil borings;

• Four grab groundwater samples from four temporary wells;

• Fifteen (15) QA/QC samples.

An SI is conducted when the PA determines an AOI exists based on probable use, storage, and/or 

disposal of PFAS-containing materials. The SI includes multi-media sampling at AOIs to 

determine whether or not a release has occurred. The SI may conclude further investigation is 

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

required. Additionally, the CSMs were refined to assess whether a potentially complete pathway 

exists between the source and potential receptors for potential exposure at the AOIs, which are 

described in Section 7. 

8.2 Outcome 

Based on the results of this SI, further evaluation is warranted in an RI for AOI 1: Former Cal FIRE 

FTA and AOI 2: Former META Yard FTA; no further evaluation is warranted for AOI 3, AOI 4, and 

AOI 6 at this time. AOI 5 was not evaluated during this investigation. Based on the CSMs 

developed and revised in light of the SI findings, there is potential for exposure to drinking water 

receptors from AOI 1 and AOI 2 from sources on the facility resulting from historical DoD activities. 

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

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

the SLs is as follows: 

• At AOI 1:

• PFOA, PFOS, PFHxS, and PFNA in groundwater exceeded their SLs at AOI01-01,

with the following maximum concentrations: PFOA at 291 ng/L, PFOS at 182 ng/L,

PFHxS at 908 ng/L, and PFNA at 69.9 ng/L. PFBS was detected below the SL in

groundwater at AOI01-01. Additionally, PFOA, PFOS, and PFBS were detected

below their SLs in groundwater at SL-02, downgradient of AOI 1.

• PFOS in surface soil exceeded the SL of 13 μg/kg at AOI01-01, with a concentration

of 71.9 J μg/kg. All other detected concentrations of PFOA, PFOS, PFHxS, PFNA
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 8-2

and PFBS in soil at AOI 1 were below their SLs. Additionally, PFOA, PFOS, PFHxS, 

PFNA, and PFBS were not detected in soil at SL-02, downgradient of AOI 1. 

• Based on the exceedances of the SLs in soil and groundwater, further evaluation of

AOI 1 is warranted in an RI.

• At AOI 2:

• PFOS in groundwater exceeded the SL of 4 ng/L at AOI02-01, with a concentration

of 6.12 ng/L. PFOA, PFHxS, and PFBS were detected below their SLs in

groundwater. PFNA was not detected in groundwater at AOI 2.

• The detected concentration of PFOS in soil at AOI 2 was below the SL. PFOA,

PFHxS, PFNA, and PFBS were not detected in soil at AOI 2.

• Based on the exceedances of the SL in groundwater, further evaluation of AOI 2 is

warranted in an RI.

• At AOI 3:

• The detected concentrations of PFOS, PFHxS, and PFBS in soil were below their

SLs. PFOA and PFNA were not detected in soil. Therefore, no further evaluation is

warranted at AOI 3.

• At AOI 4:

• PFOA, PFOS, PFHxS, PFNA, and PFBS were not detected in soil. Therefore, no

further evaluation is warranted at AOI 4.

• At AOI 6:

• The detected concentrations of PFOA and PFOS in soil were below their SLs.

PFHxS, PFNA, and PFBS were not detected in soil. Therefore, no further evaluation

is warranted at AOI 6.

Due to the inability to collect groundwater at AOI 3, AOI 4 and AOI 6, there is some uncertainty 

regarding groundwater flow directions in the vicinity of these AOIs.

Of the six PFAS compounds presented in the 6 July 2022 OSD memorandum, HFPO-DA 

(commonly referred to as GenX) was not included as an analyte at the time of this SI. Based on 

the CSM developed during the PA and revised based on SI findings, the presence of HFPO-DA 

is not anticipated at the facility because HFPO-DA is generally not a component of MIL-SPEC 

AFFF and based on its history including distribution limitations that restricted use of GenX, it is 

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

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

Table 8-1 summarizes the SI results for soil and groundwater used to determine if an AOI should 

be considered for further investigation under CERCLA and undergo an RI. 
Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 8-3

Table 8-1: Summary of Site Inspection Findings and Recommendations

AOI Potential 

Release Area

Soil –

Source 

Area

Groundwater – 

Source Area

Groundwater – 

Facility Boundary Future Action

1 Former CAL 

FIRE FTA Proceed to RI 

2 Former META 

Yard FTA Proceed to RI

3 

CAL FIRE 

Cuesta Camp 

Tenant

N/A N/A No further action

4 O’Sullivan 

Airfield Shed N/A N/A No further action

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

Legend:

N/A = not applicable 

= detected; exceedance of the screening levels

= detected; no exceedance of the screening levels

= not detected
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AECOM 8-4

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Site Inspection Report

Camp San Luis Obispo, San Luis Obispo, California

AECOM 9-1

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