HomeMy WebLinkAboutPRR24079 2024-03-14 PFAS Investigation Plan
Arcadis of New York, Inc.
630 Plaza Drive
Suite 200
Highlands Ranch
Colorado 80129
Tel 718 446 0116
www.arcadis.com
Page:
1/18
Dan Niles
Engineering Geologist
Central Coast Regional Water Quality Control Board
895 Aerovista Place, Suite 101
San Luis Obispo, California 93401
Subject:
Revised Supplemental Per- and Polyfluoroalkyl Substances Sampling
Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
Dear Mr. Niles:
At the request of Chevron Environmental Management Company (CEMC), and on
behalf of Union Oil Company of California (Unocal1), Arcadis U.S., Inc. (Arcadis) has
prepared this Revised Supplemental Per- and Polyfluoroalkyl Substances Sampling
Work Plan (Revised Supplemental Work Plan) to comply with the Central Coast
Regional Water Quality Control Board’s (Regional Board’s) request for the former
San Luis Obispo Tank Farm Project located in San Luis Obispo County, California
(SLO Tank Farm or Site; Figure 1). This Revised Supplemental Work Plan was
developed in response to the Regional Board’s letter rejecting the Supplemental Per-
and Polyfluoroalkyl Substances Sampling Workplan (2023 Supplemental Work Plan;
Arcadis 2023) dated October 23, 2023 (2023 Letter; Regional Board 2023). The
2023 Supplemental Work Plan was developed in response to the Water Board’s
letter denial of a request for No Further Action (NFA) and request for a workplan
addendum dated December 9, 2022 (2022 Letter; Regional Board 2022). A response
to comments received in the 2023 Letter is included as Attachment A. Arcadis
submitted a Per- and Polyfluoroalkyl Substances Sampling Results Investigation
Report on January 21, 2022 (Arcadis 2022) to the Regional Board detailing results of
an initial investigation that was conducted in accordance with the investigation activities outlined in the
Per- and Polyfluoroalkyl Substances Sampling Work Plan (Work Plan; Arcadis 2020). CEMC concluded
that the SLO Tank Farm Former Fire Training Area (FFTA) did not appear to be a source contributing to
PFAS impacts observed in the downgradient off-site water supply wells nor the onsite water supply wells
1 The original Regional Board request received indicates the subject property as Former Unocal. Use of
the term Union Oil is more appropriate as Unocal is a separate corporate entity. For the purposes of
continuity with the Regional Board request Unocal is used throughout this Revised Supplemental Work
Plan.
ENVIRONMENT
Date:
February 9, 2024
Contact:
Steve Rice
Phone:
303.710.7537
Email:
Steve.Rice@arcadis.com
Our ref:
30083564
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
2/18
(WSW-NW and WSW-SW). This conclusion was based on the interpretation of the groundwater sampling
and monitoring results, coupled with the historical records that the FFTA used firefighting foam that did not
contain PFAS.
Furthermore, the data collected and publicly available data suggested that upgradient sources, including
the San Luis Obispo County Regional Airport (Airport), a 2018 Union Pacific Railroad Tie Fire, and
potentially other unidentified/unconfirmed regional contributors, are impacting groundwater beneath the
SLO Tank Farm. The 2022 Letter indicated that the Board believes presence of Perfluorohexanesulfonic
acid (PFHxS) and Perfluorobutanesulfonic acid (PFBS) detected in groundwater monitoring wells near the
FFTA suggests that PFAS-containing aqueous film-forming foam (AFFF) was used at the FFTA, despite
documentation that non-PFAS-containing Foamite was used during the SLO Tank Farm operational
period. The highest detections of PFBS and PFHxS compounds observed in groundwater were along the
hydrogeologically upgradient eastern property boundary, adjacent to the Airport, indicating influence of
off-site and upgradient sources. Known and potential off-site PFAS sources are discussed in further detail
in Section 1.4 below.
1 SITE BACKGROUND
The Site is located at 276 Tank Farm Road, south of the City of San Luis Obispo in western San Luis
Obispo County, California (Figure 1). The Site is approximately 332 acres in size and is currently
bordered generally by the Airport (southeast), light industrial development (west), agricultural and pastoral
lands (south), light industrial (north, south, east, and west), and residential neighborhoods (east). The Site
is divided into north and south sections by Tank Farm Road.
1.1 SITE HISTORY
In 1910, Unocal constructed the Site as a central storage location for crude oil that was transferred via
pipeline from the San Joaquin Valley and Santa Maria oil fields. At peak use, the maximum storage
capacity for the Site was more than six (6) million barrels, comprising of six (6) large earthen reservoirs
with capacities ranging from 775,000 to 1,350,000 barrels and 21 aboveground storage tanks (ASTs) with
capacities of 55,000 barrels each. Operations at the Site gradually declined during the latter decades of
the 20th century. In 1926, a lightning strike ignited a fire that ultimately burned most of the 6.3 million
barrels of oil in inventory (this fire pre-dated the invention and use of PFAS-containing AFFF). After the
fire, four (4) of the original reservoirs and ten (10) of the original ASTs were reconstructed. Reservoir
locations are shown on Figure 5.
Operations at the Site gradually declined during the latter decades of the 20th century. The Site was
operational through the early 1980s, and by the late 1990s the Site was formally decommissioned. The
remaining four reconstructed reservoirs were decommissioned between the 1950s and 1970s as follows:
Reservoir 5 (decommissioned in 1959)
Reservoirs 3 and 6 (1961)
Reservoir 4 (1976).
For the ten (10) remaining or rebuilt ASTs, one (1) was removed in the early 1960s; eight (8) of the nine
(9) remaining ASTs were removed in 1994; and the final AST (55524), which was used to store water for
fire suppression, was removed in 2000 (Marine Research Specialists 2013). AST locations are shown on
Figure 5.
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
3/18
During a portion of the facility’s operational period, an area approximately 200 x 500 square feet (outlined
in orange on Figure 5) that was part of the Northwest Operations Area of the site was used as an FFTA.
The FFTA was used to practice extinguishing flammable-liquid fires using simulated process equipment,
which were fed petroleum products from onsite tanks. Currently, the site is primarily characterized as
open space, comprised of undeveloped grassland and wetland. Offices and a parking lot in the Northwest
Operations Area, north of Tank Farm Road, are in use. Remediation activities in the past few years have
included equipment removal, wetland restoration, and regrading. Remediation activities performed in
2019 at the FFTA included the removal of the firefighting trench, excavation of the top two (2) feet of soil,
scarification and compaction of approximately one (1) foot of material beneath the excavated material,
and the addition of a six (6) foot cap over the FFTA (Trihydro 2020). Groundwater monitoring is being
conducted on a semi-annual basis, with a focus on impacts associated with petroleum hydrocarbons.
1.2 GEOLOGY AND HYDROGEOLOGY
The Site is located within the Coast Ranges Geomorphic Province of California. The Site is situated at the
western end of the San Luis Valley, which is a basin filled with Holocene-aged alluvium (Dibblee 2004).
The bedrock of the Franciscan Formation unconformably underlies the alluvium and crops out at the
northeastern corner of the Site. The alluvium thickness at the Site increases towards the southwest from
0 feet, where bedrock is exposed, to a maximum thickness of approximately 160 feet at the southwestern
corner. Shallow groundwater zones have limited connectivity to the deeper groundwater zones (e.g.,
greater than 50 feet beneath ground surface [ft bgs]; Avocet 2011). Groundwater supply wells in the area
are drilled and completed into the deeper zones. Stormwater from the east, north, and west flows into the
SLO Tank Farm Site. A significant portion of the Site resides within a 100-year floodplain and has a
history of flooding during major precipitation events (Avocet 2015).
1.2.1 SHALLOW AND DEEP SATURATED ZONES
Avocet (2011) noted that the degree of hydraulic communication between the shallow, petroleum-
impacted, and deep (>50 ft bgs) saturated zones, was evaluated based on aquifer tests performed
along Tank Farm Road in 1992 and 1996. The aquifer tests used two purpose-built “water supply” wells
installed within or immediately adjacent to petroleum-impacted soils. Testing before, during, and after
the 24-hour aquifer tests determined that no contaminants had been drawn into the wells from the
overlying impacted soils, despite 20 feet of drawdown. As such, the memo concluded that the
connection between the shallow and deep (>50 ft bgs) saturated zones is limited (Avocet 2011). In
addition, in 2001, multi-level probes were installed to evaluate vertical conductivity adjacent to
petroleum impacted areas. Evaluation of the resulting data showed that there are no consistent upward
or downward gradients within the aquifer above the resolvable level of about 0.003 feet per foot (ft/ft)
(England Geosystem 2002). This data analysis supports a lack of hydraulic communication between
shallow groundwater at the SLO Tank Farm and the deeper off-site supply wells located on properties
downgradient and cross-gradient (Whitson Industrial Park Well 01 [screen interval 60 – 115 feet btoc],
Holdgrafer & Associates Well 01 [screen interval unknown], and Copeland S. Properties Well 01 [screen
interval 100 – 170 feet btoc]). Groundwater PFAS results from both on-site and off-site groundwater wells
(including the off-site supply wells) are identified in Figure 2.
1.2.2 HISTORICAL WATER SUPPLY WELLS
The March 31, 2015 Final Remedial Action Plan (2015 RAP) identified two (2) historical water supply
wells in the Northwest Operations Area. The approximate locations of the wells were unable to be verified
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
4/18
and “It is likely that the wells were abandoned many years ago and any other record of them has long
since been lost” (Avocet 2015). The 2023 Letter requested that “a discussion of the final determination
regarding location efforts for proper abandonment of these wells” be included in this Revised
Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan. Historical records and well
completion reports were reviewed to identify the status of the 12-inch diameter supply wells in the
Northwest Operations Area. Additionally, geophysical subsurface investigations for these wells were
completed as part of the Northwest Operations Area excavation and capping effort. The historical records
review and subsurface investigations did not identify the presence of supply wells nor did they confirm
proper abandonment of the wells. Additional historic record review is ongoing. Any new significant
findings, or a revised factual timeline, will be presented in the investigation report as appropriate.
1.3 POTENTIAL ON-SITE FIREFIGHTING FOAM STORAGE AND USE AREAS
Site activities that may be associated with foam storage and use include: (a) maintaining a firefighting
system using water for suppression of petroleum-liquid fires and (b) the FFTA (outlined in orange on
Figures 2 and 5), which historically stored non-PFAS containing Foamite. As noted in the 2023
Supplemental Work Plan, a fire occurred in 1926 that pre-dated use of PFAS-containing AFFF, which was
first used in the 1960s by the US Navy but not available to general industry until the 1970s when National
Fire Protection Association (NFPA) added the “military specification” (MILSPEC) to its design
requirements for refineries (ITRC 2020). Therefore, no Site impacts from PFAS could be associated with
the 1926 event. Site operations south of Tank Farm Road had ceased by 1961, when the last reservoirs
south of the road were removed. Site areas that are identified for potential foam storage and/or use occur
within the operational areas north of Tank Farm Road, particularly in the Northwest Operations Area. The
investigation relating to potential releases of PFAS by Unocal operations is focused on the Northwest
Operations Area.
Since operations at the Site date back to 1910, interpreting the Regional Board’s 2020 Letter to
investigate PFAS has required historical records review, which is still ongoing. The Regional Board states
in its 2020 Letter “references describe training specifically for petroleum fires, which would likely have
involved the use and/or storage of a class of fire suppressing materials known as “aqueous film forming
foam” (AFFF), which generally contain PFAS.” Available historical records for the SLO Tank Farm (from
1937-1985) do not support the Regional Board’s generalized hypothesis. Historical records identified to
date demonstrate a firefighting system that was designed to use products and techniques that pre-date
the development and use of PFAS-containing AFFF: Specifically, records review suggests the following:
Historical records indicate that the facility had a PFAS-free “Foamite” firefighting system. No
records or information have been located to support the use of PFAS-containing AFFF foams on
property by Unocal.
An on-site water tank was present for use in fire suppression. The exact location of the water tank
varied through the years.
The facility fire suppression system was designed to distribute water throughout the operational
areas of the property. AST 55524, north of the Northwest Operations Area, was re-purposed to
store water from on-site wells2; it was also the most recent water tank demolition in 2000. The
2 AST 55524 in earlier drawings (pre-1981) is listed as having a "floating roof". That indicated AST 55524
would have been used as a product tank. Later depictions (post-1981) show AST 55524 with a "cone
wood" top, which would indicate use as a water tank. The actual transition date to use as a water tank is
uncertain.
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
5/18
water was distributed throughout the facility via a network of aboveground and underground
pipelines. AST 55524 was used to store water for fire suppression, dating back to at least 1981,
and was kept intact longer than other ASTs in the area (through 2000). As indicated in the Unocal
fire suppression system engineering drawing (Unocal 1956/1981), a “fire pump” was formerly
located southeast of the former AST 55524.
Foam tanks near tanks 55526, 55534, 55536, and 55538 were added to the Unocal fire
suppression system engineering drawing in 1981 (Unocal 1956/1981). Except for AST 55534, the
soils near these former foam tanks were regraded during subsequent remediation and restoration
activities in 2018 (Padre 2019).
At four (4) locations within the northern tank farm, foam tanks and/or foam risers were positioned
along the water distribution system (Unocal 1956, revised 1981). The Foamite distribution system
for floating roof tanks was made popular with US patent US2548409 in 1951.
Numerous fire hydrants and risers were located along this distribution system.
Use of non-PFAS-containing foam powder (“Foamite”)3 was documented, and likely was the
extinguishing agent between 1928-1977, as NFPA only added bulk fuel storage
recommendations to consider PFAS-containing MILSPEC AFFF after 1972 committee reports. A
drill in December 1977 used Foamite canisters and follow-up explained that no conversion to
“liquid foam” had yet occurred.4
Site maps refer to storage of Foamite, which does not contain PFAS (patents for Foamite
systems 1918-1960; Foamite Firefoam 1925). References to “Foamite lines” occur in maps as
early as 1923 and 1928, and foam powder was noted in historical (1974) records as exceeding an
age of 20 years.
Based on review of historic fire loss reports from the 1970s, the only fire at the SLO Tank Farm,
between 1970 and 1980, occurred when a boiler fire box exploded on 9 Jan 1976. At the time,
Foamite powder was still on-site. No record of the details of the 9 Jan 1976 fire response (if any)
was located in archives, but a subsequent December 1977 drill used Foamite canisters as
conversion to “liquid foam” had yet occurred.4 Foam tanks were added to engineering drawings
in 1981, but no other identified records indicate any Foamite lines or other equipment was
changed.
The lateral water distribution pipelines between the northern tank field are identified as Foamite
(Unocal 1991).
The facility had an established FFTA on-site. A Unocal publication from Fall 1988 explaining that
since 1980, week-long annual fire training occurred at a fire school in another state.5
3 To make Foamite, “a portion of the spent [licorice] root from the primary extractors is subjected to a
secondary extraction with a 5 per cent solution of caustic soda under 100 pounds steam pressure for
several hours. This secondary extract is evaporated to 12° Be, in which form it is known as Firefoam
Liquid and is used as a foam stabilizer in the Foamite fire extinguisher. The solutions in this extinguisher
have the following composition: the first, 11 parts aluminum sulfate and 89 parts water; the second, 8
parts sodium bicarbonate, 3 parts Firefoam Liquid (12° Be.), and 89 parts water. On mixing these
solutions a tough, durable foam, which resists heat and mechanical abuse, is produced. This method of
attacking fires has proved to be of great value in extinguishing oil fires and is now in almost universal use
in the protection of oil tanks.” (Houseman PA and Lacey 1929)
4 Per 25 January 1978 fire drill critique, a 22 December 1977 San Luis Obispo Tank Farm drill used
Foamite canisters as the SLO Tank Farm had not yet converted from foam powder to liquid foam
concentrate.
5 See Unocal Fall 1988 issue of its publication, Seventy-Six, pages 30-35.
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
6/18
Cessation of use of the FFTA is consistent with aerial photos that indicate that the FFTA was not
in active use after 1978 (Attachment B of the previously submitted Supplemental Work Plan)
An additional water storage tank for fire suppression is currently present in the Northwest
Operations Area, east of the parking lot, and south of the existing office buildings. The 10,000-
gallon polyethylene tank was installed sometime between 2000 to 2015 after operations at the
Site had ceased and after most petroleum infrastructure had been removed. The tank is
connected to a system of hydrants across the Site (Avocet 2015) and is not associated with
conveyance or use of AFFF for petroleum liquid fires. The tank is filled with water collected from a
permitted on-site non-potable water supply well (WSW-NW).
Given the above facts, there is no evidence to suggest that PFAS-containing AFFF was ever used by
Unocal, or others, at the SLO Tank Farm.
1.3.1 FORMER FIRE TRAINING AREA
Based on available records identified to date, the FFTA operated in the Northwest Operations Area until
1979 and was used to practice extinguishing flammable-liquid fires. Petroleum hydrocarbons were fed via
buried metal pipes to practice fixtures in a concrete-and-asphalt-lined pit within the FFTA. The area
consisted of several simulated sumps, flares, and tanks where personnel practiced techniques for
extinguishing petroleum-fed fires fueled by off-specification gasoline and diesel fuel. Aerial photo
interpretation indicates the FFTA was established sometime prior to 1947 and well maintained until 1978,
after which time the area appears in a diminished state until 2003 where the FFTA is no longer visibly
maintained. Newspaper articles are available for a few years, indicating that outside fire agencies held
periodic fire training drills at the SLO Tank Farm in 1972 (Santa Maria Times 1972), 1976 (Five Cities
Times-Press-Recorder 1976) and 1985 (San Luis Obispo County Telegram-Tribune 1985). It is unclear if
these events included the Unocal employees or if these were situations of outside entities utilizing the
SLO Tank Farm FFTA. Beginning in 1980, Unocal began annual fire training at an out-of-state fire school
(Seventy-Six, Fall 1988, pages 30-35).
In 2019, the concrete trench and underlying pipelines associated with the training area were removed
from the SLO Tank Farm and transported to the Santa Maria Landfill for waste disposal. Removed
pipelines were transported to Bedford Enterprises, Inc. to be recycled. The Northwest Operations Area
was excavated to a depth of at least two (2) feet below original grade to remove arsenic impacted soil.
The FFTA was then backfilled with clean material and is now capped with up to six (6) feet of clean fill
(Trihydro 2021).
1.4 PREVIOUS PFAS INVESTIGATION
At the request of the Regional Water Board, groundwater gauging and sampling activities were conducted
on October 21-22, 2021, at the SLO Tank Farm. Ten (10) monitoring wells (MW-17, MW-19, MW-26,
MW-41, MW-43, MW-49, MW-50, SLOW-12, SLOW-17, and SLOW-18) were gauged with a water level
meter before sampling. In addition, though not identified in the Work Plan, the SLO Tank Farm’s water
supply well southwest (WSW-SW) and its respective above ground storage tank (storage tank) were
included in the PFAS gauging and sampling event. The SLO Tank Farm’s (WSW-NW) was then sampled
during a separate mobilization on April 21, 2022. Representative groundwater sample locations selected
(MW-41, MW-49, MW-50, SLOW-12, SLOW-17, SLOW-18, and WSW-NW) are located approximately
250 to 350 feet down- and cross-gradient of the FFTA, as shown on Figure 2. In addition, select
monitoring wells around the east, south, and southwest perimeter (MW-17, MW-19, MW-26, MW-43, and
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
7/18
WSW-SW) of the SLO Tank Farm were sampled to evaluate background groundwater conditions and the
possibility of off-property influence moving on-site from the Airport (Figure 2).
Concentrations of various PFAS compounds were detected in all monitoring wells (including perimeter and
FFTA representative wells), the water supply wells, and storage tank samples collected, although SLOW-
12, SLOW-18, and MW-50 did not have any PFAS concentrations above the Limit of Quantitation (LoQ)
(e.g., only “J-flagged” estimated values below the LoQ). The highest detected concentrations of PFAS
compounds observed in groundwater at the Site were upgradient along the east and southeastern
boundary of the SLO Tank Farm, downgradient of the adjacent Airport and adjacent to the tributary for the
East Fork of the San Luis Obispo Creek. The analytical data for samples collected along the eastern
property boundary demonstrate a similar PFAS distribution pattern compared to that from samples
collected for the Airport investigation described below (i.e., dominated by PFHxS and
Perfluorooctanesulfonic acid [PFOS]; Figure 2).
For the areas downgradient of the FFTA, the concentrations of PFAS in the samples were so minimal that
it is difficult to interpret the PFAS signature of the samples, but the signature appeared to also mimic the
plume emanating from the Airport.
1.5 KNOWN AND POTENTIAL OFF-SITE SOURCES IDENTIFIED TO DATE
CEMC continues to evaluate additional potential off-site sources of PFAS that could be impacting media
at or beneath the SLO Tank Farm. Within one (1) mile of the SLO Tank Farm, industrial and commercial
properties that are current potential sources of PFAS have been identified through desktop research and
are shown in Figure 1. Facilities of greatest interest include:
San Luis Obispo Regional Airport (Geotracker Case ID T10000012768): The Airport is a
known source of PFAS directly adjacent to the Site (Figure 1). Previous reports for the Airport
identified it as a source of PFAS to both soil and groundwater in the area (Roux Associates
2022). The 2023 Airport Remedial Investigation Workplan identified groundwater flow “flowing to
the northwest into the southeastern portion of the Airport-vicinity, then turning to the west and
southwest further into the San Luis Obispo Basin” (Roux Associates 2023). The highest PFAS
concentrations in soil and groundwater at the Airport are associated with the Airport’s fire station
(CAL FIRE San Luis Obispo County Fire Station 21) on the northeastern side of the airport,
approximately 5,000 feet east of the Site’s southeastern boundary. PFOS concentrations near the
fire station were reported to be as high as 1,900 micrograms per kilogram (µg/kg) (at 10 feet bgs
in boring NE-1C) in soil and 130,000 nanograms per liter (ng/L) in the perched groundwater
sample at NE-1D (Roux Associates 2023). PFHxS was also present in the groundwater at the
Airport with concentrations up to 790,000 ng/L reported at NE-1D. The recent private well
sampling conducted by the Airport demonstrates the PFAS plume is migrating off-site, and
potentially onto the southern boundary of the SLO Tank Farm, with PFOS concentrations in one
private well as high as 910 ng/L (PW-04; Roux Associates 2022). The Airport Stormwater
Drainage System Map indicates that stormwater collected from the current AFFF storage area,
historical fire training area, and former stormwater retention basin is captured and routed to a
detention basin (Outfall #6 – Figure 5) at the north end of runway 11-29 (Roux Associates 2022).
The stormwater is then discharged to a drain outlet in the East Fork of the San Luis Obispo
Creek. While the East Fork of the San Luis Obispo Creek provides a hydraulic barrier to surface
water flow, groundwater flowing below the creek continues onto the Site, influencing
concentrations under the SLO Tank Farm. In February 2023, the Airport investigation collected
sediment and surface water to identify potential off-site sources emanating upstream from Acacia
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
8/18
Creek onto the Airport. The sampling identified PFAS detections in surface water ranging from 74
to 140 ng/L for PFOS; and 72 to 87 ng/L for PFHxS within Acacia Creek and upstream of Tank
Farm Road (Roux Associates 2023; Figures 3A and 3B).
Union Pacific Railroad (UPRR) Tie Fire (Geotracker Case ID T10000012125): The UPRR Tie
Fire is a known source of PFAS discharge to an upstream tributary of Acacia Creek, which flows
onto the SLO Tank Farm. On 16 May 2018, two local fire departments (San Luis Obispo City and
San Luis Obispo Regional Airport6) released 300 gallons of 3 percent (%) AFFF C-303 Foam
Concentrate into the draining area of the creek in response to a fire of five UPRR rail cars
containing railroad ties (Figure 1). The drainage channel in which the fire suppressant
wastewater/AFFF mixture flowed through is a tributary of Acacia Creek, which borders the
Southeast SLO Tank Farm property boundary, adjacent to the Airport (Figure 5). Two (2)
separate investigations have occurred, and a third investigation is pending. Surface water within
the tributary to Acacia Creek was sampled as part of the initial response investigation. Laboratory
results from the surface water collected in the incident area and downstream channel indicated
elevated PFAS concentrations within the creek. Sample L3, located 100 feet downstream of the
incident area was reported to contain PFBS, PFHxS, PFOS, and PFOA concentrations of 5,200
ng/L, 32,000 ug/L, 58 ng/L, and 1,800 ng/L, respectively. Sample L4 consisted of surface water
from the incident area and was reported to contain PFBS, PFHxS, PFOS, and PFOA
concentrations of 4.5 ug/L, 39 ug/L, 59 ug/L, and 1.7 ug/L, respectively (Arcadis 2018b).
San Luis Auto Salvage Yard: San Luis Auto Salvage Yard maintains an active industrial
stormwater discharge permit (Attachment B; Envrionmental.com Compliance Group 2015) for
indirect discharge into the flood control storm channel on the Site, upgradient from the three (3)
off-site water supply wells identified by the Regional Board in a letter dated August 7, 2020 (2020
Letter; Regional Board 2020). The United States Environmental Protection Agency (USEPA)
recently released guidance summarizing PFAS considerations for stormwater discharges from
auto salvage yards, recognizing that there are many sources of PFAS in these types of facilities
and PFAS are likely present in the discharge from this type of industrial operation (USEPA
2021a). PFAS have been documented as used in various parts of automobiles including in the
car body, engines, electronics, environmental systems, fuel systems, interiors, steering systems,
suspension/brakes, and transmission (Gluge et al., 2020). No testing has been previously
conducted to determine if this facility is a source of PFAS to the area. Due to the known presence
of PFAS in auto salvage operations and the permitted stormwater discharge onto CEMC
property, CEMC proposes to sample stormwater flowing from the San Luis Auto Salvage Yard
during a precipitation event (Figure 5).
Metal Finishing: The USEPA has recently recognized metal finishing as a PFAS point source
category requiring PFAS monitoring in National Pollutant Discharge Elimination System
(NPDES) permits per Preliminary Effluent Guidelines Program Plan 15 (USEPA 2021b). At least
two metal fabrication facilities are in close proximity to both the Site and three (3) off-site water
supply wells identified by the Regional Board in a letter dated August 7, 2020 (2020 Letter;
Regional Board 2020). No publicly available testing has been conducted to determine if these
facilities are a source of PFAS in the area.
Circuit Board and Electronic Manufacturers: PFAS are known to be used by the electronics
industry in the production of printed circuit boards and many other electronic products (Gluge et
6 California Department of Forestry and Fire Protection (CAL FIRE) operates the fire station at the airport
under contract with San Luis Obispo County.
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
9/18
al., 2020). At least two printed circuit board and electronic manufacturing facilities are in close
proximity to both the Site and the three water supply wells identified by the Regional Board in a
letter dated August 7, 2020 (2020 Letter; Regional Board 2020). No publicly available testing has
been conducted to determine if these facilities are a source of PFAS in the area.
SLO WWTP (Geotracker Case ID NPD100051582): The San Luis Obispo Wastewater
Treatment Plant (WWTP) is located less than a mile to the northwest of the Site (Figure 1). In a
State and Regional Water Board’s questionnaire (Order WQ 2020-0015-DWQ), the WWTP
indicated they accept a continuous flow of wastewater from a metal fabrication facility.
Perfluoropentanoic acid (110 ng/L) was detected in a 2021 wastewater sample (2100976-01,
collected on 2/11/21; Oilfield Environmental & Compliance, Inc 2021). While the biosolids and
wastewater effluent have been tested for PFAS and shown to be “non-detect” for most measured
PFAS in 2021 analyses, the detection limits on these samples is relatively high (>10,000
nanogram per kilogram [ng/kg] for biosolids and >50 ng/L for liquid samples) and all precursor
PFAS are not measured in the analysis (City of San Luis Obispo Public Utilities 2021).
City of San Luis Obispo Fire Training Site: The SLO Tank Farm’s 2015 Remedial Action Plan
identified an off-site fire training area northwest of the Site. The training area was used by the City
of San Luis Obispo Fire Department and located adjacent to the WWTP (Avocet 2015). Municipal
fire stations have been implicated as sources of PFAS to the environment through historical and
current use and storage of AFFF (Young et al., 2021 and MPART 2024). No publicly available
testing has been conducted to determine if this facility is a source of PFAS in the area.
City of San Luis Obispo Wastewater Lift Station: A municipal lift station associated with the
WWTP is located adjacent to the Northwest Operations Area’s western boundary. In 2023, a
solicitation request to replace several fittings, check valves, and 81 linear feet of 8” diameter pipe
was submitted (California Bid Network 2023). A description of the solicitation request stated, “This
project will replace failing discharge pipes.” No testing has been conducted to determine if this
facility is a source of PFAS in the area. Neither a record of release nor investigation of the failing
discharge pipe to identify potential environmental impacts have been identified in the records
review.
Automotive Body Shops: PFAS have been previously identified as used in weather resistant
paint, as well as in automotive waxes and polishes (Gluge et al., 2020). At least two autobody
shops are in close proximity to the Site as well as the three (3) off-site water supply wells
identified by the Regional Board in a letter dated August 7, 2020 (2020 Letter; Regional Board
2020). No publicly available testing has been conducted to determine if these facilities are a
source of PFAS in the area.
Review and evaluation of additional potential off-site sources of PFAS will continue. Figure 6 shows all
potential facilities identified to date within one (1) mile of the SLO Tank Farm, which includes
approximately 140 industrial and commercial properties potentially associated with PFAS usage such as
aerospace, electronics, chemical/pesticide manufacturing, automobile repair, painting and metal work and
salvage, metal coating etc..
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
10/18
2 PROPOSED SAMPLING LOCATIONS
All sampling points proposed as part of this investigation are identified in Table 1. All media (e.g., soil,
groundwater, sediment) will be sampled as part of the investigation. Sampling is designed to address the
area around the former FFTA with additional surface water and stormwater sampling locations to identify
potential contributors of PFAS to the SLO Tank Farm.
2.1 SOIL INVESTIGATION
Eleven (11) Soil samples (BG-1 through BG-11) will be collected to assess background concentrations in
the vicinity of the Site, to determine if there are elevated PFAS concentrations in soil and potentially
associated with off-site sources, as well as for comparison purposes to verify whether the FFTA is a
source of PFAS in soil (Figure 5). Nine (9) soil boring (FFTA-1 through FFTA-9) locations are proposed at
and/or near the FFTA. The locations were selected based on the former footprint of the FFTA, specifically
beneath and around the former training trench. One soil sample location, FFTA-9, was selected after
ongoing records review identified the historic (1976) boiler fire box explosion in the Northwest Operation
Area. It is unknown what materials were used to suppress the 1976 explosion. Two (2) soil sampling
horizons will be collected, inclusive of the first native horizon and the capillary fringe to address prior soil
disturbances associated with surface soil remediation. A first native soil sample is expected to be
collected from approximately 7 to 8 feet below current ground surface at the FFTA.
Eleven (11) background soil sample locations will be collected (North / South / East property boundaries
and off-site to the west [BG-11]) from areas undisturbed by former Unocal Site operations at three (3)
horizon depths for comparison purposes. The sampled soil horizon depths will include surface soil, a soil
horizon that matches the first native FFTA soil locations, and the capillary fringe. The background
locations were selected such that any historic operations at the FFTA would not have impacted soil in
these areas. The background location results will undergo statistical analysis using the procedure outlined
in the Unified Guidance provided by the USEPA, 2009 (USEPA 2009) and the most current version of
USEPA statistical software package ProUCL. Appropriate nonparametric or comparison methods will be
used to establish representative background soil concentrations, independent of potential operational
impacts, for the SLO Tank Farm.
Upon review of patents, the major components of Foamite powder are aluminum sulfate, sodium
bicarbonate, and caustic soda treated licorice root extract (Houseman PA and Lacey 1929). Based on this
composition, aluminum levels will be measured in soil from the FFTA samples and compared against
results from locations BG-1 through BG-11. If a Foamite inorganic signature is detected under or near the
FFTA, then it will support the determination that this type of non-PFAS containing foam was used during
training.
2.2 GROUNDWATER INVESTIGATION
To increase the accuracy of groundwater flow data at the SLO Tank Farm property, including the FFTA,
up to seven (7) temporary piezometers will be installed within the unconsolidated overburden (silty and
lean clays with interbeds of fine-grained silty sand and poorly to well-graded sands and gravels) within
and along the perimeter of the Site to support a Site-wide hydraulic gradient evaluation. Each piezometer
will be gauged and surveyed. The resulting water level information will be used to prepare a contoured
potentiometric surface map to evaluate current groundwater flow directions across the Site. Initial data will
be included in the supplemental work plan report. Following installation and initial gauging at each
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
11/18
location, the piezometers will be left in place and groundwater gauging data recorded quarterly for up to
one (1) year to identify any seasonal changes in data collection. The piezometers will then be abandoned.
In accordance with the Regional Board’s 2022 and 2023 Letters to further investigate PFAS in
groundwater at the FFTA (Regional Board 2022; Regional Board 2023), Chevron proposes eight (8)
vertical aquifer profiling (VAP) with hydraulic profiling tool (HPT) locations hydraulically downgradient and
cross-gradient of the FFTA (VAP-1 through VAP-4, and VAP-10 through VAP-13 locations shown on
Figure 5). HPT borings will initially be advanced to obtain continuous horizontal hydraulic conductivity (K)
profiles through alluvium and to determine specific VAP sampling intervals (high permeability zones). The
HPT data will be reviewed nightly by the Arcadis project geologist to make informed decisions about
subsequent VAP sampling intervals. The target VAP sampling intervals will be intentionally biased toward
more permeable zones, where groundwater will be more readily available for sampling.
Following completion of the HPT investigation, VAP step-outs will then be drilled at each of the eight (8)
locations down- and cross-gradient from the FFTA to collect groundwater samples. Groundwater samples
will be collected at five (5) or ten (10)-foot intervals from the water table to approximately 40 feet (or the
bedrock interface) at three (3) of eight (8) downgradient/cross-gradient locations. The target groundwater
sampling intervals and frequency will be determined based on HPT results, as discussed above. Five (5)
of the eight (8) downgradient VAP-HPT locations will be advanced to approximately 20 feet below the top
of the bedrock interface or until refusal (estimated total depth of 50 to 75 feet below native ground
surface), with samples collected at five (5) or ten (10)-foot intervals. The FFTA downgradient VAP-HPT
transect (VAP-1 through VAP-4) will be installed with approximately 80 linear feet of spacing between
locations.
In addition to the eight (8) borings near the FFTA, an additional three (3) VAP-HPT borings (VAP-5
through VAP-7 locations shown on Figure 5) will be advanced in a transect north and east (upgradient) of
the FFTA, oriented generally perpendicular to groundwater flow. Furthermore, two (2) additional VAP/HPT
locations will be advanced along the southeast property boundary (VAP-8 and VAP-9; Figure 5) to
establish what, if any, concentrations and relative abundance/patterns of individual PFAS in shallow
groundwater that may be flowing onto and across the Site from the Airport. These additional locations will
be similarly drilled to approximately 20 feet below the top of the bedrock interface or until refusal
(estimated total depth of 35 to 50 feet below current ground surface). Proposed groundwater evaluation
locations for background and the FFTA are shown on Figure 5. If results of the potentiometric surface
map identify a groundwater flow direction that is different from expected, the three (3) perimeter
groundwater investigation locations (VAP-5, VAP-6, and VAP-7) may be modified.
Additionally, vertical hydraulic conductivity will be evaluated by advancing a step-out location through
alluvium to the bedrock interface at each of the thirteen (13) VAP-HPT borehole locations. Undisturbed
soil cores will be collected by Shelby tube (or equivalent) and submitted for laboratory vertical
permeability and geophysical parameter analysis.
If possible, drilling will be conducted without the addition of drilling fluids. If drilling fluids are required
based on drilling conditions, then fluorescein dye will be added to the drilling fluids. During subsequent
groundwater sampling, the tracer dye will be used to visually confirm when unimpacted native
groundwater enters the borehole. The tracer dye would be used to identify the dilution of groundwater by
drilling fluids and if correction factors/groundwater purging is required to collect a representative sample.
Any use of fluorescein dye as a drilling fluid additive will be in accordance with Central Coast Regional
Water Board Order R3-2019-0089.
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
12/18
2.3 SEDIMENT AND SURFACE WATER INVESTIGATION
In accordance with the Regional Board’s 2022 Letter to investigate PFAS in sediment (Regional Board
2022), Chevron proposes eight (8) sediment and surface water sampling locations at the various creeks
and surface drainages that enter or cross the SLO Tank Farm property. The locations were selected
based on creek flow paths and property entry points. One (1) location was selected based on its
downstream proximity to the Airport stormwater outfall #6 and drain outlet location (Figure 5). Sediment
and surface water samples collected will inform whether detectable concentrations of PFAS in sediment
and surface water may be from upgradient/upstream surface water flow direction either leading towards
the FFTA or traversing the creek along the southeast property boundary. Though surface water samples
were not specifically requested by the Regional Board, results of sediment and surface water sampling
will expand the dataset collected during the Airport’s investigation of sediment and surface water in
Acacia Creek (Figures 3A and 3B). In addition to expanding the Airport investigation dataset, results will
be used to identify possible PFAS contamination from Airport runoff and during flooding events that
frequently occur at the Site. Proposed sediment and surface water sampling locations are shown on
Figure 5.
Sediment samples will be collected from the upper 0 to 6 inches of native creek bed sediment using
dedicated Push Core Lexan tubes. The tube will be driven with a straight vertical entry into the top 6
inches of native sediment at the pre-determined locations. The tube will then be capped with a PFAS-free
high-density polyethylene (HDPE) liner on either end. An alternative approach may be used depending on
field conditions, including use of a stainless-steel scoop or trowel if the creeks are not flowing. All
equipment will be thoroughly decontaminated, or single use, in accordance with Arcadis’ PFAS guidance
documents (Arcadis 2021; Attachment E of the 2023 Supplemental Work Plan).
2.4 STORMWATER INVESTIGATION
A stormwater outfall from the adjacent San Luis Auto Salvage Yard (Figure 5) was identified during
review of potential off-site sources of PFAS (Environmental.com Compliance Group 2015). Due to the
outfall’s proximity to the off-site supply wells and potential for PFAS conveyance onto the Site, Arcadis
proposes the collection of one stormwater sample immediately downstream of the stormwater outfall, on
CEMC property. A stormwater sample will be collected from location SW-1 (Figure 5) within four hours of
the start of discharge from a Qualified Storm Event (QSE) rain event, which is defined as “any
precipitation event that produces a discharge for at least one drainage area and is preceded by 48 hours
with no discharge from any drainage area. Weather and precipitation forecasts will be tracked to identify
potential QSEs. When targeting a QSE for stormwater sampling, the appropriate team member will
weekly consult the National Oceanographic and Atmospheric Administration for weather forecasts. These
forecasts can be obtained at http://www.srh.noaa.gov/. If weekly forecasts indicate potential for significant
precipitation, the weather forecast will be closely monitored during the 48 hours preceding the event
(California Stormwater Quality Association 2014). An exact sampling date is thus unknown for the
planned stormwater sample collection following work plan approval. Sampling will be performed in
accordance with the Arcadis-Chevron PFAS Field Sampling Guidance (Arcadis 2021; Attachment E of the
2023 Supplemental Work Plan).
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
13/18
3 SAMPLING METHODOLOGY
Arcadis’ PFAS sampling guidance provides PFAS-specific instructions on how to sample various
environmental media for analysis of PFAS consistent with the Interstate Technology Regulatory Council’s
(ITRC’s) Site Characterization Considerations, Sampling Precautions, and Laboratory Analytical Methods
for PFAS (Attachment D of the 2023 Supplemental Work Plan). These instructions include restrictions on
the use of materials that can introduce PFAS through cross-contamination.
Soil sampling will be performed in accordance with the PFAS Sampling and Analysis Guidance for
Chevron Corporation (Arcadis 2021; Attachment E of the 2023 Supplemental Work Plan). VAP
groundwater PFAS sampling will be performed via a low-flow sampling method using either a stainless-
steel or peristaltic pump and HDPE and silicone tubing, in accordance with the September 2020
California State Water Quality Control Board PFAS Sampling Guidelines for Non-Drinking Water
(California State Water Quality Control Board 2020), Arcadis guidance on PFAS Sampling Procedures
(Arcadis 2018a), Low-Flow Groundwater Purging for Monitoring Wells and the Arcadis-Chevron PFAS
Field Sampling Guidance (Arcadis 2020; Attachment E of the 2023 Supplemental Work Plan), and
Arcadis’ Technical Guidance Instruction for VAP sampling with considerations for PFAS substances
(Arcadis 2022b; Attachment F of the 2023 Supplemental Work Plan). Water quality parameters, which
include dissolved oxygen (DO), conductivity, temperature, pH, and turbidity, will be measured through a
flow cell (Table 2 below). Samples will be centrifuged by the analytical laboratory if the final recorded
turbidity parameter is above 10.0 nephelometric turbidity units (NTU). Sediment and surface water
sampling will be performed in accordance with the PFAS Sampling and Analysis Guidance for Chevron
Corporation (Arcadis 2021; Attachment E of the 2023 Supplemental Work Plan), updated to incorporate
the Board request to use (draft) EPA Method 1633. The samples will be shipped by priority overnight to
Eurofins Lancaster Laboratories (Eurofins) in Lancaster, Pennsylvania.
Table 2. Field Parameter List Applicable to Groundwater Samples
From each groundwater investigation location, undisturbed soil cores will be collected from the native
formation for vertical permeability testing and geophysical parameters to assess hydraulic properties and
the potential for vertical PFAS migration. At each selected groundwater investigation location, an
undisturbed soil core sample will be collected by advancing Shelby Tubes (or equivalent). Continuous soil
cores will be collected from the unconsolidated aquifer. The soil core samples will be submitted to a
certified laboratory for analysis of vertical permeability and geophysical parameters listed in Table 3
below.
Field Parameters
Depth to Water
DO
Temperature
Electrical Conductivity
pH
Turbidity
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
14/18
Table 3. Vertical Permeability and Geophysical Parameters Applicable to Groundwater Investigation
Locations
3.1 QUALITY ASSURANCE/QUALITY CONTROL
As part of the field quality assurance/quality control (QA/QC), matrix spike/matrix spike duplicate
(MS/MSD) samples, field blanks, equipment blanks, and field duplicate samples (Table 1) will be
collected in accordance with the Quality Assurance Project Plan (QAPP) requirements (Attachment H of
the 2023 Supplemental Work Plan), updated to accommodate the Board request to use (draft) EPA
Method 1633.
4 LABORATORY ANALYSES
The proposed sampling analyte list and their target reporting limits for PFAS analytes are shown in Table
4. At the request of the Regional Board, the constituent list to be tested for has been updated to match
the State Water Board’s December 6, 2022, “Target Reporting Limits” table (2023 Letter; Regional Board
2023). PFAS analysis will be completed using EPA draft Method 1633 unless noted otherwise. Three
PFAS compounds (10:2 Fluorotelomer sulfonic acid, Perfluorooctadecanoic acid, and
Perfluorohexadecanoic acid) requested by the Regional Board cannot be analyzed by draft Method 1633
and will therefore be analyzed using EPA method 537 Version 1.1 modified. No other compounds will be
reported using EPA method 537 Version 1.1 modified besides the three compounds identified previously.
The laboratory will provide a Level IV fully documented data deliverable. Environmental Standards, Inc.
will perform a third-party data validation and data usability summary report.
A QAPP provides data quality objectives and additional QA/QC protocols to be used in data collection
activities. The QAPP will be used during the project execution and data evaluation and was provided in
Attachment H of the 2023 Supplemental Work Plan. The QAPP will undergo updates prior to the field
investigation to accommodate the Board request to use (draft) EPA Method 1633 in conjunction with the
three compounds being analyzed by EPA method 537 Version 1.1 modified.
Parameters
Vertical permeability in accordance with ASTM International (ASTM) standard test
method ASTM D5084
Porosity in accordance with ASTM D7263
T Grain size distribution in accordance with ASTM D6913
Particle size distribution of fine-grained soil (between 75 and 0.2 micrometer) in
accordance with ASTM D7928
Moisture content in accordance with ASTM D2216
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
15/18
5 REPORTING
After the investigation is complete and laboratory data are received and validated, Arcadis will prepare an
investigation report summarizing the sampling and analytical results. Geotracker reporting will be
completed.
6 SCHEDULE
The PFAS investigation event is tentatively scheduled to be performed upon the Regional Board’s
approval of this Work Plan. Arcadis will initiate the sampling work described above within 90 days of the
Regional Board’s approval. An investigation report with results will be provided to the Regional Board
within 90 days of receipt of final validated laboratory results. The final validated laboratory data will be
uploaded to GeoTracker.
Please direct any questions, comments, or correspondence regarding this project to Steve Rice, Arcadis
Project Manager and copy Owen Ranta and James Beacom of CEMC on all written correspondences.
Sincerely,
Arcadis U.S., Inc.
Steve Rice
Program Manager
Copies:
Johnsie Lang, Arcadis
Owen Ranta, CEMC
James Beacom, CEMC
Enclosures:
Tables
1 Sampling Locations and Methods
2 Field Parameter List Applicable to Groundwater Samples (in text)
3 Vertical Permeability and Geophysical Parameters Applicable to Groundwater Investigation
Locations (in text)
4 PFAS Analyte List
Figures
1 Site Location Map
2 Water Well Analytical Results
3A Sediment PFAS Concentrations – Acacia Creek
3B Surface Water PFAS Concentrations – Acacia Creek
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
16/18
4 Northwest Operations Area – Features and Proposed Soil Sampling Points
5 Proposed Sampling Locations
6 Potential PFAS Source Locations
Attachments
A Response to Regional Board’s Comments Provided in 2023 Letter
B San Luis Auto Salvage Industrial Stormwater Discharge Permit Documentation
References
Arcadis. 2018a. PFAS Sampling Procedures and Low-Flow Groundwater Purging for Monitoring Wells.
June 19.
Arcadis 2018b. Tie Fire Response Summary Report, San Luis Obispo, CA – May 16, 2018 Tie Fire
Incident. October 5.
Arcadis. 2020. Per- and Polyfluoroalkyl Substances Sampling Work Plan, San Luis Obispo Tank Farm,
San Luis Obispo, California. September 30.
Arcadis. 2021. Poly- and Perfluoroalkyl Substance (PFAS) Sampling and Analysis Guidance for Chevron
Corporation. June 25.
Arcadis. 2022. Per- and Polyfluoroalkyl Substances Sampling Results Investigation Report, San Luis
Obispo Tank Farm, San Luis Obispo, California. January 21.
Arcadis. 2022b. TGI – Vertical Aquifer Profile (VAP) Sampling. Rev: 2.0. June 15.
Arcadis. 2023. Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan, San Luis Obispo
Tank Farm, San Luis Obispo, California. March 17.
Avocet Environmental, Inc. 2011. Technical Memorandum: Environmental Issues Concerning Future Water
Supply Wells, Former San Luis Obispo Tank Farm, San Luis Obispo, California. Prepared for Bill
Almas, Chevron Business and Real Estate Services. December 2.
Avocet. 2015. Final Remedial Action Plan, San Luis Obispo Tank Farm, 276 Tank Farm Road, San Luis
Obispo, California. March 31.
California Stormwater Quality Association. 2014. Stormwater Pollution Prevention Template, BMP
Handbook Portal: Industrial and Commercial. September.
California State Water Quality Control Board. 2020. Per- and Polyfluoroalkyl Substances (PFAS)
Sampling Guidelines for Non-Drinking Water. September.
California Bid Network. 2023. Tank Farm Lift Station Discharge Pipe Replacement.
https://www.californiabids.com/bid_opportunities/2023/10/11/12959065-tank-farm-lift-station-
discharge-pipe-replacement.html. Accessed January 11, 2024.
City of San Luis Obispo Public Utilities. 2021. City of San Luis Obispo Water Resource Recovery Facility
PFAS Summary Report. March 13.
Dibblee, T.W. Jr. 2004. Geologic Map of the San Luis Obispo Quadrangle, California.
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
17/18
England Geosystem, Inc. 2002. Supplemental Site Characterization Report, Unocal San Luis Obispo
Tank Farm, San Luis Obispo, California. Prepared for Central Coast Group, Unocal
Corporation. January 10.
Environmental.com Compliance Group. 2015. Storm Water Pollution Prevention Plan, San Luis Auto
Salvage. Waste Discharge Identification Number 3 40I024911. August 10.
Five Cities Times-Press-Recorder (Arroyo Grande, California), 1976. Industrial Fire Drills Scheduled.
Friday, November 5, 1976. Retrieved from: Microsoft Outlook - Memo Style (ca.gov)
Foamite equipment patents (various). 1918-1960.
Foamite Firefoam. 1925. Extinguishing Oil and Other Fires; the Foamite Firefoam Method. Retrieved
from: https://archive.org/details/ExtinguishingOilAndOtherFiresTheFoamiteFirefoamMethod
Gluge, J. et al. 2020. “An Overview of The Uses of Per- and Polyfluoroalkyl Substances (PFAS).” The
Royal Society of Chemistry. Environmental Science Processes & Impacts, 22, 2346.
Houseman, P.A. and Lacey, H.T. 1929. “The Licorice Root in Industry” Industrial and Engineering
Chemistry. October. 915–917. The Licorice Root in Industry (acs.org)
ITRC. 2020. PFAS – Section 3: Firefighting Foams. April 14. Retrieved from: https://pfas-1.itrcweb.org/3-
firefighting-foams/#3_1
Marine Research Specialists. 2013. Chevron Tank Farm Remediation and Development Project, Final
Environmental Impact Report. December.
Michigan PFAS Action Response Team. 2024. Firefighting Foam and PFAS.
https://www.michigan.gov/pfasresponse/investigations/firefighting-foam. Accessed February 8.
Oilfield Environmental & Compliance, Inc. 2021. Analytical Report for Project WWTP PFAS. March 23.
Padre. 2019. 2018 Annual Summary Report, Remediation and Restoration Activities. Chevron San Luis
Obispo Tank Farm Remediation and Restoration Project, San Luis Obispo County, California. April.
Regional Board. 2020. Site Cleanup Program: Chevron (Former Unocal) – Tank Farm Road Bulk
Storage, 276 Tank Farm Road, San Luis Obispo, San Luis Obispo County – Requirement for PFAS
Investigation Workplan Pursuant to California Water Code 13267. August 7.
Regional Board. 2022. Site Cleanup Program: Chevron (Former Unocal) – Tank Farm Road Bulk
Storage, 276 Tank Farm Road, San Luis Obispo, San Luis Obispo County – Denial of No Further
Action and Requirements to Comply with California Water Code 13267 Order Dated August 7, 2020.
December 9.
Regional Board. 2023. Site Cleanup Program: Chevron (Former Unocal) – Tank Farm Road Bulk
Storage, 276 Tank Farm Road, San Luis Obispo, San Luis Obispo County – Rejection of
Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan. October 23.
Roux Associates, Inc. 2022. Supplemental PFAS Investigation Report. San Luis Obispo County Regional
Airport, 975 Airport Drive, San Luis Obispo, California. July 29
Roux Associates, Inc. 2023. Per- and Polyfluoroalkyl Substances (PFAS) Site Conceptual Model. San
Luis Obispo County Regional Airport, 975 Airport Drive, San Luis Obispo, California. October 19.
San Luis Obispo County Telegram – Tribune, 1985. County Digest – Training Fire Tuesday. Wednesday
October 30, 1985. Retrieved from: Microsoft Outlook - Memo Style (ca.gov)
Mr. Dan Niles
February 9, 2024
arcadis.com
Page:
18/18
Santa Maria Times. 1972. Union Oil Fire School announcement. Tuesday March 14, 1972. Retrieved
from: Microsoft Outlook - Memo Style (ca.gov)
Seventy Six. Fall 1988. Retrieved from:
https://static1.1.sqspcdn.com/static/f/765516/27948662/1531847651683/Fall+1988.pdf?token=XxTJo
Dg7gR5C7VgMlcQKpjoZxmk%3D
Trihydro. 2020. 2019 Annual Summary Report, Remediation and Restoration Activities, Chevron San Luis
Obispo Tank Farm Remediation and Restoration Project, San Luis Obispo County, California. April
15.
Trihydro. 2021. 2020 Annual Summary Report, Remediation and Restoration Activities, Chevron San Luis
Obispo Tank Farm Remediation and Restoration Project, San Luis Obispo County, California. April
15.
Unocal. 1956. Revised 1981. Fire Protection Map, San Luis Obispo Tank Farm, San Luis Obispo Dist.,
San Luis Obispo County, Calif. Sheet D2A713. Union Oil Company of California. July 27.
Unocal. 1991. General Arrangement San Luis Obispo Tank Farm Northern California Division Pipeline.
Unocal Corporation. Los Angeles, CA. January.
United States Environmental Protection Agency. 2009. Statistical Analysis of Groundwater Monitoring
Data at RCRA Facilities. Unified Guidance. March.
United States Environmental Protection Agency. 2021a. Industrial Stormwater Fact Sheet Series,
Sector M: Automobile Salvage Yards. EPA-883-F-06-028. February.
United States Environmental Protection Agency. 2021b.Preliminary Effluent Guidelines Program
Plan 15. EPA-HQ-OW-2021-0547; FRL-5601.5-01-OW. Federal Register. Volume 86,
Number 175. September 14.
United States Environmental Protection Agency. 2024. PFAS Analytic Tools.
https://awsedap.epa.gov/public/extensions/PFAS_Tools/PFAS_Tools.html. Accessed
January 11.
Young et al. 2021. Per- and Polyfluoroalkyl Substances (PFAS) and Total Fluorine in Fire Station
Dust. J Expo Sci Environ Epidemiol. September 31 (5): 930-942.
Tables
Table 1
Sampling Locations and Methods
San Luis Obispo Tank Farm
San Luis Obispo, California
Page:
1/4
Sample
Type Medium Location
ID
Rationale Sample Collection Location Sample
Method
Sample
Type
Number of
Samples Analytes
San Luis
Obispo
Tank Farm
Soil
FFTA-1 Former fire school AST
location
First native and capillary fringe
Grab
N 2
PFAS / Aluminum
FFTA-2 Former fire school AST
location N 2
FFTA-3 Former fire school location N 2
FFTA-4 West perimeter of FFTA
Trench N 2
FFTA-5 North perimeter of FFTA
Trench N 2
FFTA-6 East perimeter of FFTA
Trench N 2
FFTA-7 South perimeter of FFTA
Trench N 2
FFTA-8 Center of FFTA Trench N 2
FFTA-9 Beneath historic boiler N 2
BG-1 Northwest property
boundary
Surface, horizon matching first
native from FFTA, and capillary
fringe
N, MS/MSD,
FD 5
BG-2 North/central property
boundary
N, MS/MSD,
FD 5
BG-3 North/central property
boundary
N, MS/MSD,
FD 5
BG-4 Northeast property
boundary N 3
BG-5 Northeast property
boundary N 3
BG-6 East property boundary N 3
BG-7 East property boundary,
south of tank farm road N 3
BG-8 Southeast property
boundary N 3
BG-9 Southeast property
boundary N 3
BG-10 Southeast property
boundary N 3
BG-11 Off property – west of FFTA N 3
San Luis
Obispo
Tank Farm
Groundwater /
soil lithology
VAP-1 Downgradient of FFTA; to
bedrock interface High “K” zone, every 5’ to 10’
Low flow N 3 to 8 PFAS / HPT /
Permeability /
Geophysical Parameters VAP-2 Downgradient of FFTA; to
bedrock interface Low flow N 3 to 8
Table 1
Sampling Locations and Methods
San Luis Obispo Tank Farm
San Luis Obispo, California
arcadis.com
Page:
2/4
Sample
Type Medium Location
ID
Rationale Sample Collection Location Sample
Method
Sample
Type
Number of
Samples Analytes
VAP-3 Downgradient of FFTA; to
bedrock interface+20 feet Low flow N 7 to 14
VAP-4 Downgradient of FFTA; to
bedrock interface Low flow N 3 to 8
VAP-5 Upgradient of FFTA; to
bedrock interface+20 feet Low flow N, MS/MSD,
FD* 13 to 20
VAP-6 Upgradient of FFTA; to
bedrock interface+20 feet Low flow N, MS/MSD,
FD* 13 to 20
VAP-7 East property boundary; to
bedrock interface+20 feet Low flow N, MS/MSD,
FD* 13 to 20
VAP-8
Southeast property
boundary; to bedrock
interface+20 feet
Low flow N 7 to 14
VAP-9 South property boundary; to
bedrock interface+20 feet Low flow N 7 to 14
VAP-10
Downgradient of FFTA and
south of Tank Farm Rd; to
bedrock interface+20 feet
Low flow N 7 to 14
VAP-11
Cross gradient of FFTA at
unnamed creek; to bedrock
interface+20 feet
Low flow N 7 to 14
VAP-12
Cross gradient of FFTA and
adjacent to sewer
pumphouse; to bedrock
interface+20 feet
Low flow N 7 to 14
VAP-13
Offsite and Cross gradient
of FFTA; to bedrock
interface+20 feet
Low flow N 7 to 14
San Luis
Obispo
Tank Farm
Stormwater SW-1
Downgradient of San Luis
Auto Salvage Yard
Stormwater Discharge, on
Chevron property
Stormwater, during
precipitation event Grab N 1 PFAS
San Luis
Obispo
Tank Farm
Sediment and
Surface Water
(collocated)
SED -2
SW-2
West Fork of Tank Farm
Creek entry onto property
Upper 6-inches of native creek
bed and surface water
Grab N 2
PFAS / Moisture Content
(sediment only)
SED-3
SW-3
East Fork of Tank Farm
Creek entry onto property Grab N, MS/MSD,
FD 6
SED-4
SW-4
Acacia Creek entry onto
property Grab N 2
SED-5
SW-5
Acacia Creek, downstream
of Airport Outfall Grab N 2
Table 1
Sampling Locations and Methods
San Luis Obispo Tank Farm
San Luis Obispo, California
arcadis.com
Page:
3/4
Sample
Type Medium Location
ID
Rationale Sample Collection Location Sample
Method
Sample
Type
Number of
Samples Analytes
SED-6
SW-6
Drainage leading from NW
Operations Area, at Tank
Farm Road culvert
Grab N 2
SED-7
SW-7
Tank Farm Creek, at Tank
Farm Road culvert Grab N 2
SED-8
SW-8
Tank Farm Creek,
downstream of Tank Farm
Road
Grab N 2
SED-9
SW-9
Downgradient of the San
Luis Auto Salvage Yard
stormwater discharge,
within drainage feature on
Chevron property
Grab N 2
Equipment
Blanks
PFAS-Free
Water
SLO-EB-X
Stainless steel hand auger,
stainless-steel trowel, or
acetate liner (soil sampling)
See
Section
4.1
EB
Variable, up
to 55
PFAS
SLO-EB-X Drilling cutting shoe (VAP) 13
SLO-EB-X Clean HDPE tubing 1
SLO-EB-X
Submersible Pump
Variable, one
per
groundwater
sample
location (up to
180)
SLO-EB-X
Depth to water meter
Variable, one
per
groundwater
sample
location (up to
180)
SLO-EB-X Lexan tube or stainless-steel
trowel (sediment)
Variable, up
to 8
Field
Blanks
PFAS-Free
Water
SLO-FB-
X-
MMDDYY
YY
One per day. N/A FB One per day PFAS
Table 1
Sampling Locations and Methods
San Luis Obispo Tank Farm
San Luis Obispo, California
arcadis.com
Page:
4/4
Notes:
EB = equipment blank MS/MSD = matrix spike/matrix spike duplicate
FB = field blank N = normal
FD = field duplicate N/A = not applicable
HDPE = high-density polyethylene TBD = To be determined
*If a fourth, or fifth, MS/MSD is needed during groundwater sampling (due to QAPP frequency requirements – 1/20 samples), the final MS/MSD will be collected from the deepest sampled
interval at VAP-4, VAP-5, and VAP-6, in addition to the shallow interval.
Table 4
PFAS Analyte List
San Luis Obispo Tank Farm
San Luis Obispo, California
Chemical
Abstracts
Service
(CAS) No.
Perfluoroundecanoic acid PFUA/PFUdA 2058-94-8 2.00 0.500 0.200 0.0500
Perfluorotridecanoic acid PFTriA/PFTrDA 72629-94-8 2.00 0.500 0.200 0.0500
Perfluorotetradecanoic acid PFTA/PFTeDA)376-06-7 2.00 0.500 0.200 0.0500
Perfluoropentanoic acid PFPeA 2706-90-3 4.00 1.00 0.400 0.100
Perfluorododecanesulfonic acid PFDoS 79780-39-5 2.00 0.900 0.200 0.0500
Perfluoropentanesulfonic acid PFPeS 2706-91-4 2.00 0.500 0.200 0.0500
Perfluorooctanoic acid PFOA 335-67-1 2.00 0.640 0.200 0.0510
Perfluorooctanesulfonic acid PFOS 1763-23-1 2.00 0.500 0.200 0.0510
Perfluorooctanesulfonamide PFOSA 754-91-6 2.00 0.500 0.200 0.0500
Perfluorooctadecanoic acid*PFODA 16517-11-6 3.00 1.00 0.600 0.200
Perfluorononanoic acid PFNA 375-95-1 2.00 0.500 0.200 0.0500
Perfluorononanesulfonic acid PFNS 68259-12-1 2.00 0.400 0.200 0.0500
Perfluorohexanoic acid PFHxA 307-24-4 2.00 0.500 0.200 0.0590
Perfluorohexanesulfonic acid PFHxS 355-46-4 2.00 0.570 0.200 0.0500
Perfluorohexadecanoic acid*PFHxDA 67905-19-5 3.00 1.00 0.600 0.200
Perfluoroheptanoic acid PFHpA 375-85-9 2.00 0.520 0.200 0.0500
Perfluoroheptanesulfonic acid PFHpS 375-92-8 2.00 0.400 0.200 0.0500
Perfluorododecanoic acid PFDoDA 307-55-1 2.00 0.500 0.200 0.0500
Perfluorodecanoic acid PFDA 335-76-2 2.00 0.500 0.200 0.0500
Perfluorodecanesulfonic acid PFDS 335-77-3 2.00 0.500 0.200 0.0500
Perfluorobutanoic acid PFBA 375-22-4 8.00 2.00 0.800 0.100
Perfluorobutanesulfonic acid PFBS 375-73-5 2.00 0.300 0.200 0.0500
N-methyl perfluorooctanesulfonamido ethanol N-MeFOSE 24448-09-7 20.0 5.00 2.00 0.500
N-methyl perluorooctanesulfonamide NMeFOSA 31506-32-8 2.00 0.500 0.200 0.0500
N-methylperfluorooctanesulfonamidoacetic acid N-MeFOSAA 2355-31-9 4.00 1.20 0.200 0.0500
N-ethyl perfluorooctanesulfonamido ethanol N-EtFOSE 1691-99-2 20.0 5.00 2.00 0.500
N-ethyl perfluorooctanesulfonamide N-EtFOSA 4151-50-2 2.00 0.500 0.200 0.0500
N-ethylperfluorooctanesulfonamidoacetic acid N-EtFOSAA 2991-50-6 2.00 0.700 0.200 0.0500
Hexafluoropropylene Oxide Dimer Acid HFPO-DA 13252-13-6 8.00 2.00 0.800 0.0510
4,8-Dioxa-3H-perfluorononanoic acid ADONA 919005-14-4 8.00 1.50 0.800 0.200
9-Chlorohexadecafluoro-3-oxanonane-1-sulfonic acid 9-Cl-PF3ONS 756426-58-1 8.00 1.00 0.800 0.200
11-Chloroeicosafluoro-3-oxaundecane-1-sulfonic acid 11-Cl-PF3OdS 763051-92-9 8.00 2.00 0.800 0.200
10:2 Fluorotelomer sulfonic acid*10:2 FTS 120226-60-0 5.00 1.00 2.00 0.600
8:2 Fluorotelomer sulfonic acid 8:2 FTS 39108-34-4 8.00 2.60 1.00 0.350
6:2 Fluorotelomer sulfonic acid 6:2 FTS 27619-97-2 8.00 2.50 1.00 0.350
4:2 Fluorotelomer sulfonic acid 4:2 FTS 757124-72-4 8.00 1.70 0.800 0.200
Perfluoro-3-methoxypropanoic acid PFMPA 377-73-1 4.00 0.500 0.400 0.104
Perfluoro(4-methoxybutanoic acid)PFMBA 863090-89-5 4.00 0.100 0.400 0.100
Perfluoro-3,6-dioxaheptanoic acid NFDHA 151772-58-6 4.00 0.100 0.400 0.100
Perfluoro (2-ethoxyethane) sulfonic acid PFEESA 113507-82-7 4.00 0.500 0.400 0.100
2H, 2H, 3H, 3H-perfluorohexanoic acid 3:3 FTCA 356-02-5 10.0 1.50 1.00 0.250
2H, 2H, 3H, 3H-perfluorooctanoic acid 5:3 FTCA 914637-49-3 50.0 10.0 5.00 1.00
2H, 2H, 3H, 3H-perfluorodecanoic acid 7:3 FTCA 812-70-4 50.0 10.0 5.00 1.00
Notes:
ng/L = nanogram per liter
ng/g = nanogram per garm
* = To be analyzed using EPA Method 537.1 Modified
All other chemicals to be analyzed by EPA Draft Method 1633
Chemical Name Abbreviation Groundwater Minimum
Detection Limit (ng/L)
Soil Minimum Detection
Limit (ng/g)
Soil/Sediment Reporting
Limit (ng/g)
Groundwater Reporting
Limit (ng/L)
Page 1 of 1
Figures
Union Pacific Rail Road Tie Fire
San Luis Auto Salvage
City of San Luis Obispo Wastewater
Tank Farm Lift Station
City of San Luis Obispo
Wastewater Treatment Plant
City of San Luis Obispo
Fire Training Site
San Luis Obispo Regional
County Airport 35°15'50"N35°15'40"N35°15'30"N35°15'20"N35°15'10"N35°15'0"N35°14'50"N35°14'40"N35°14'30"N35°14'20"N35°14'10"N35°14'0"N35°13'50"N35°15'40"N35°15'30"N35°15'20"N35°15'10"N35°15'0"N35°14'50"N35°14'40"N35°14'30"N35°14'20"N35°14'10"N35°14'0"N35°13'50"N35°13'40"N120°38'0"W120°38'10"W120°38'20"W120°38'30"W120°38'40"W120°38'50"W120°39'0"W120°39'10"W120°39'20"W120°39'30"W120°39'40"W120°39'50"W120°40'0"W120°40'10"W120°40'20"W120°40'30"W120°40'40"W120°40'50"W120°41'0"W120°41'10"W120°41'20"W120°41'30"W
120°37'50"W120°38'0"W120°38'10"W120°38'20"W120°38'30"W120°38'40"W120°38'50"W120°39'0"W120°39'10"W120°39'20"W120°39'30"W120°39'40"W120°39'50"W120°40'0"W120°40'10"W120°40'20"W120°40'30"W120°40'40"W120°40'50"W120°41'0"W120°41'10"W120°41'20"W
0 1,500 3,000
SCALE IN FEET
I
SITE LOCATION MAP
User Name: ski01076 DATE: 2/8/2024 1:05 PMPATH: T:\_ENV\Chevron_PFAS_SLO_Tank_Farm\MXD\2023\Chevron_PFAS_SLO_Tank_Farm_2023.aprxTOPOGRAPHIC SOURCE:
U.S. Geological Survey
https://ngmdb.usgs.gov/topoview/
REFERENCES:
USGS Topographic Quadrangles:
San Luis Obispo, Lopez Mountain,
Pismo Beach, and Arroyo Grande NE,
California
7.5-Minute Series
PROJECTIONS:
NAD 1983 State Plane California V Feet
FORMER CHEVRON SAN LUIS OBISPO TANK FARM
SAN LUIS OBISPO, CALIFORNIA
FIGURE
1
P a c i f i c O c e a n
Site Location
California
Nevada Utah
Oregon Idaho
Arizona
<<<!(@A
!(@A
!(@A!(@A !(@A!(@A!(@A
!(@A
!(@A
!(@A
!<
!<
@A
@A
@A
@A
@A@A
@A
@A
@A
@A
@A
@A
@A
@A@A
!<
!<
!<
!<
!(
!(
!(!(
!(
!(!(
!(
!(
Water Supply Well (SW) MW-3
Copeland S. Properties, Well 01 AcaciaCreekWhitson Industrial Park, Well 01
Holdgrafer & Associates, Well 01
11-LA
MW-18
MW-35
MW-29MW-43
MW-45
MW-38MW-39
MW-47 MW-26
MW-27
MW-40
SLOW-17
MW-49
SLOW-18
SLOW-12MW-56R
MW-50
MW-48S
MW-53D
MW-48D
MW-53S
MW-41
MW-19
MW-17
36" Diameter
Gate Valve
Water Supply Well (NW)OrcuttCre
e
k
Orcutt Creek
East ForSan Luis Obispo Creek
W
estForkTank Far
m
CreekTankFarm C re e kT r ib u t a ry to EastForSanLuisObispoCreekE a s t F o rk T a nk Farm C r e e k
Acadia Cree
k
PW-65
PW-63
PW-66
PW-56
PW-57
Well 01
(CA4000726)
Well 01
(CA4000216)
MW-5
MW-6 35°15'0"N35°14'30"N35°15'0"N35°14'30"N120°39'0"W120°39'30"W120°40'0"W
120°39'0"W120°39'30"W120°40'0"W
0 600 1,200
SCALE IN FEET
I
WATER WELL ANALYTICAL RESULTS
User Name: ski01076 DATE: 1/24/2024 11:58 AMPATH: T:\_ENV\Chevron_PFAS_SLO_Tank_Farm\MXD\2023\Chevron_PFAS_SLO_Tank_Farm_2023.aprxFIGURE
2
Notes:
1. Method: 537.1 (modified) - Per- and Polyfluoroalkyl
Substances (PFAS; ng/L)
2. Bold results indicate a concentration measured
at or above the method detection limit.
3. ft btoc = feet below top of casing
4.* = GSI Water Solutions, Inc. 2022. San Luis Obispo
Valley Groundwater Basin Annual Report (Water
Years 2020-2021). San Luis Obispo Basin
Groundwater Sustainability Committee and the
Groundwater Sustainability Agencies. March 24.
5. ** = Roux Associates, Inc. 2023. Per- and Polyfluoroalkyl
Substances (PFAS) Site Conceptual Model, San Luis
Obispo County Regional Airport, 975 Airport Drive,
San Luis Obispo, California. October 19.
6. Orange = Chevron Monitoring Well Results
7. Pink = Offsite Groundwater Supply Well Results
8. Purple = Airport Groundwater Results
9. ng/L = nanogram per liter
10. J = The concentration is an approximate value
because it is less than the reporting limit but
greater than or equal to the method detection limit.
Legend
!(Private Well Sampled For PFAS**
Groundwater Sampling Location
@A Groundwater Monitoring Well (Active)
!<Groundwater Supply Well (Active)
Current Stream Channel
<Direction of Groundwater Flow*
Former Fire Training Area
Site Boundary
!(Airport Well**
Well Name MW-5P MW-5
Sample Date 5/6/2020 5/6/2020
Well Screen Interval (ft btoc)18.5' - 28.5'34' - 44'
Perfluorooctanoic acid (PFOA)53 54
Perfluorobutanesulfonic acid (PFBS)44 47
Perfluorohexanesulfonic acid (PFHxS)150 B 180 B
Perfluorooctanesulfonic acid (PFOS)430 480
Well Name MW-6P MW-6
Sample Date 5/5/2020 5/5/2020
Well Screen Interval (ft btoc)9.5' - 19.5'36.5' - 51.5.'
Perfluorooctanoic acid (PFOA)35 3.7
Perfluorobutanesulfonic acid (PFBS)34 4.5
Perfluorohexanesulfonic acid (PFHxS)130 B 15 B
Perfluorooctanesulfonic acid (PFOS)180 B 4.6 B
Well Name PW-56
Sample Date 11//9/2022
Screen unknown
Perfluorooctanoic acid (PFOA)58
Perfluorobutanesulfonic acid (PFBS)59
Perfluorohexanesulfonic acid (PFHxS)310
Perfluorooctanesulfonic acid (PFOS)73
Well Name PW-57
Sample Date 4/13/2023
Screen unknown
Perfluorooctanoic acid (PFOA)14
Perfluorobutanesulfonic acid (PFBS)38
Perfluorohexanesulfonic acid (PFHxS)160
Perfluorooctanesulfonic acid (PFOS)48
Well Name PW-65
Sample Date 5/31/2023
Screen unknown
Perfluorooctanoic acid (PFOA)5.8
Perfluorobutanesulfonic acid (PFBS)22
Perfluorohexanesulfonic acid (PFHxS)78
Perfluorooctanesulfonic acid (PFOS)23
Well Name PW-66
Sample Date 5/31/2023
Screen unknown
Perfluorooctanoic acid (PFOA)5.3
Perfluorobutanesulfonic acid (PFBS)21
Perfluorohexanesulfonic acid (PFHxS)71
Perfluorooctanesulfonic acid (PFOS)20
Well Name Well 01 (CA4000726)
Sample Date 2/6/2020
Screen 60 - 160
Perfluorooctanoic acid (PFOA)15
Perfluorobutanesulfonic acid (PFBS)13
Perfluorohexanesulfonic acid (PFHxS)15
Perfluorooctanesulfonic acid (PFOS)28
Well Name Holdgrafer & Associates Well 01
Sample Date 4/19/2021
Screen unknown
Perfluorooctanoic acid (PFOA)4.5
Perfluorobutanesulfonic acid (PFBS)9.3
Perfluorohexanesulfonic acid (PFHxS)43
Perfluorooctanesulfonic acid (PFOS)46
Well Name Copeland S. Properties Well 01
Sample Date 3/17/2020
Screen 100' - 170'
Perfluorooctanoic acid (PFOA)<3
Perfluorobutanesulfonic acid (PFBS)21
Perfluorohexanesulfonic acid (PFHxS)37
Perfluorooctanesulfonic acid (PFOS)53
Well Name Well 01 (CA4000216)
Sample Date 9/29/2022
Screen 50 - 65
Perfluorooctanoic acid (PFOA)4.2
Perfluorobutanesulfonic acid (PFBS)18
Perfluorohexanesulfonic acid (PFHxS)45
Perfluorooctanesulfonic acid (PFOS)54
Well Name Whitson Industrial Park Well 01
Sample Date 3/17/2020
Screen 60' - 115'
Perfluorooctanoic acid (PFOA)17
Perfluorobutanesulfonic acid (PFBS)17
Perfluorohexanesulfonic acid (PFHxS)140
Perfluorooctanesulfonic acid (PFOS)88
Well Name PW-63
Sample Date 10/20/2022
Screen unknown
Perfluorooctanoic acid (PFOA)11
Perfluorobutanesulfonic acid (PFBS)23
Perfluorohexanesulfonic acid (PFHxS)88
Perfluorooctanesulfonic acid (PFOS)54
Well Name MW-NW
Sample Date 4/21/2022
Well Screen Interval (ft btoc)80' - 140'
Perfluorooctanoic acid (PFOA)<1.6
Perfluorooctanesulfonic acid (PFBS)1.4 J
Perfluorohexanesulfonic acid (PFHxS)1.0 J
Perfluorooctanesulfonic acid (PFOS)<1.6
Well Name MW-SW
Sample Date 10/22/2021
Well Screen Interval (ft btoc)100' - 180'
Perfluorooctanoic acid (PFOA)<1.9
Perfluorooctanesulfonic acid (PFBS)2.1 J
Perfluorohexanesulfonic acid (PFHxS)5
Perfluorooctanesulfonic acid (PFOS)4.6 J
Well Name MW-17
Sample Date 10/21/2021
Well Screen Interval (ft btoc)5' - 20'
Perfluorooctanoic acid (PFOA)4.3
Perfluorooctanesulfonic acid (PFBS)42
Perfluorohexanesulfonic acid (PFHxS)59
Perfluorooctanesulfonic acid (PFOS)59
Well Name MW-19
Sample Date 10/21/2021
Well Screen Interval (ft btoc)6' - 21'
Perfluorooctanoic acid (PFOA)2.3
Perfluorooctanesulfonic acid (PFBS)22
Perfluorohexanesulfonic acid (PFHxS)59
Perfluorooctanesulfonic acid (PFOS)47 J
Well Name MW-43
Sample Date 10/21/2021
Well Screen Interval (ft btoc)10' - 25'
Perfluorooctanoic acid (PFOA)0.98 J
Perfluorooctanesulfonic acid (PFBS)25 J
Perfluorohexanesulfonic acid (PFHxS)53
Perfluorooctanesulfonic acid (PFOS)29 J
FORMER CHEVRON SAN LUIS OBISPO TANK FARM
SAN LUIS OBISPO, CALIFORNIA
FIGURE
3A PATH: T:\_ENV\CHEVRON_PFAS_SLO_TANK_FARM\MXD\2023\CHEVRON_PFAS_SLO_TANK_FARM_2023.APRX SAVED: 1/11/2024 BY: SKI01076NOTES:
1. ROUX ASSOCIATES, INC. 2023. PER- AND POLYFLUOROALKYL
SUBSTANCES (PFAS) SITE CONCEPTUAL MODEL. SAN LUIS OBISPO
COUNTY REGIONAL AIRPORT, 975 AIRPORT DRIVE, SAN LUIS OBISPO,
CALIFORNIA. OCTOBER 19.
2. SAMPLE LOCATIONS ARE APPROXIMATE.
3. UNITS IN MICROGRAMS PER KILOGRAM UG/KG.
4. ITALICIZED VALUES DENOTES DUPLICATE SAMPLES.
5. J = RESULT IS LESS THAN THE REPORTING LIMIT BUT GREATER THAN OR
EQUAL TO THE METHOD DETECTION LIMIT AND THE CONCENTRATION
IS AN APPROXIMATE VALUE.
6. G = THE REPORTED QUANTITATION LIMIT HAS BEEN RAISED DUE TO AN
EXHIBITED ELEVATED NOISE OR MATRIX INTERFERENCE.
SEDIMENT PFAS CONCENTRATIONS
ACACIA CREEK
ACR-01-1
ACR-01-2
ACR-01-3
ACR-01-4
ACR-01-1
ACR-01-2
ACR-01-3
ACR-01-4
County of San Luis Obispo, Maxar
Sample Date PFOS PFOA PFBS PFHxS
2/8/2023 1.6 0.12 J <0.29 0.16 J
2/8/2023 2.3 0.16 J <0.30 0.26 J
ACR-01-1
Sample Date PFOS PFOA PFBS PFHxS
2/8/2023 3.8 0.26 J 0.053 J 0.34
ACR-01-2
Sample Date PFOS PFOA PFBS PFHxS
2/8/2023 2.7 0.16 J <0.29 0.38
ACR-01-3
Sample Date PFOS PFOA PFBS PFHxS
2/8/2023 3.4 0.17 J <1.2 G 0.39
ACR-01-4
Legend
ROUX SEDIMENT SAMPLE LOCATION
SAN LUIS OBISPO CREEKS
SITE BOUNDARY
FORMER CHEVRON SAN LUIS OBISPO TANK
FARM SAN LUIS OBISPO, CALIFORNIA
FIGURE
3B PATH: T:\_ENV\CHEVRON_PFAS_SLO_TANK_FARM\MXD\2023\CHEVRON_PFAS_SLO_TANK_FARM_2023.APRX SAVED: 1/11/2024 BY: SKI01076NOTES:
1. ROUX ASSOCIATES, INC. 2023. PER- AND POLYFLUOROALKYL
SUBSTANCES (PFAS) SITE CONCEPTUAL MODEL. SAN LUIS OBISPO
COUNTY REGIONAL AIRPORT, 975 AIRPORT DRIVE, SAN LUIS OBISPO,
CALIFORNIA. OCTOBER 19.
2. SAMPLE LOCATIONS ARE APPROXIMATE.
3. UNITS IN NANOGRAMS PER LITER (NG/L).
4. NL=SWRCB DIVISION OF DRINKING WATER NOTIFICATION LEVEL FOR
PFOS, PFOA, PFBS & PFHXS RESPECTIVELY IS 6.5, 5.1,
500 & 3 NG/L.
5. RL=SWRCB DIVISION OF RESPONSE LEVEL FOR PFOS, PFOA, PFBS &
PFHXS RESPECTIVELY IS 40, 10, 5,000 & 20 NG/L.
6. GREEN TEXT INDICATES CONCENTRATION ABOVE NL ADVISED BY THE
STATE OF CALIFORNIA DIVISION OF DRINKING WATER.
7. RED TEXT INDICATES CONCENTRATION ABOVE DRINKING WATER RL
ADVISED BY THE STATE OF CALIFORNIA DIVISION OF
DRINKING WATER.
8. ITALICIZED VALUES DENOTES DUPLICATE SAMPLES.
SURFACE WATER
PFAS CONCENTRATIONS
ACACIA CREEK
ACR-01-1
ACR-01-2
ACR-01-3
ACR-01-4
ACR-01-1-W
ACR-01-2-W
ACR-01-3-W
ACR-01-4-W
County of San Luis Obispo, Maxar
Legend
ROUX SURFACE WATER SAMPLE LOCATION
SAN LUIS OBISPO CREEKS
SITE BOUNDARY
Sample Date PFOS PFOA PFBS PFHxS
2/8/2023 80 10 26 72
2/8/2023 88 11 29 79
ACR-01-1-W
Sample Date PFOS PFOA PFBS PFHxS
2/8/2023 79 11 32 80
ACR-01-2-W
Sample Date PFOS PFOA PFBS PFHxS
2/8/2023 74 12 33 82
ACR-01-3-W
Sample Date PFOS PFOA PFBS PFHxS
2/8/2023 140 13 33 87
ACR-01-4-W
FORMER CHEVRON SAN LUIS OBISPO TANK
FARM SAN LUIS OBISPO, CALIFORNIA
ORIGINAL
BUILDING
ORIGINAL
BUILDING
EXISTING FIRE
WATER TANK
TANK FARM ROAD
FORMER FIRE
SCHOOL
LOCATION TRENCH USED BY THE
FORMER FIRE SCHOOL
FORMER PUMP
STATION
LOCATION
(REMOVED)
MAIN ACCESS
GATE
B-33
B-35
B-36
SLOW-18
MW-50
MW-56
SLOW-12
MW-49 ACCESS ROADAPPROXIMATE
LOCATION OF
EXISTING
SEPTIC TANK &
LEACH LINES 6" WATER
8" RELIEF LINE8"8" BYP
A
S
S 10"3"8"8"16"6"
16"16"16"8"16"
3"
10"
8" RELIEF
10"
16"
LOCATION OF ABANDONED AND
DEMOLISHED FORMER HEATER
FORMER GASOLINE
AST LOCATION
EXISTING
OIL LINE "A"
4" GAS LINE
2" GAS LINE 2" GAS LINE REPORTED
TO BE ABANDONED
STORAGE
CONTAINER
APPROXIMATE LOCATION
OF EXISTING SEPTIC TANK
PADS FOR
FORMER FIRE
PUMPS
APPROXIMATE LOCATION
OF ABANDONED WATER
SUPPLY WELL No. 2
16" PIPE LINE
FOUNDATION OF FORMER
ELECTRICAL HOUSE
VAULTS
VAULTS
FORMER LINE
No. 2 TO SANTA
MARGARITA
APPROXIMATE LOCATION
OF ABANDONED 12" DIA.
WELL No. 1
APPROXIMATE LOCATION OF
FORMER 55,000 BBL ABOVE
GROUND TANK - AST 522
(DEMOLISHED BETWEEN
1959 AND 1965)
FORMER FIRE SCHOOL
AST LOCATIONS
APPROXIMATE LOCATION OF
FORMER 55,000 BBL ABOVE
GROUND TANK
(NOT REBUILT AFTER 1926 FIRE)
APPROXIMATE LOCATION OF
FORMER 55,000 BBL ABOVE
GROUND TANK - USED FOR
FIRE WATER STORAGE FROM
APPROXIMATELY 1994-2004
(REMOVED AUGUST 2000)
APPROXIMATE LOCATION OF FORMER
55,000 BBL ABOVE GROUND TANK
(REMOVED 1994)
LEACH FEILD
NEW MODULAR
OFFICE BUILDING
PETROLEUM
TESTING
LABORATORY
OPERATIONAL WATER SUPPLY
WELL (SUPPLIES NON-POTABLE
WATER TO SITE)
FOUNDATION OF
FORMER BOILER AND
TANK LOCATIONS
SCALE
0 80 160 FEETV:\1212_Padre-Chevron_SLOTF\1212.001_Remedial_Design\013_1212.001_Historical_Operations_Area.dwg\04/17/14N
SITE PROPERTY BOUNDARY
TOPOGRAPHIC CONTOUR
FENCEX
LEGEND
125
EXISTING LIGHT POLE
FIRE HYDRANT
EXISTING MONITORING / PRODUCTION WELL
WATER LINE
DRAIN LINE
CRUDE OIL
GAS - CRUDE OIL
GAS - OIL
NOTES:
1. FIGURE ONLY SHOWS THE PRINCIPAL HISTORIC
ELEMENTS OF THE OPERATIONS AREA. THE AERIAL
PHOTOGRAPH ILLUSTRATES THE CURRENT
CONDITIONS. THE HIGHLIGHTED ELEMENTS WERE
IN-PLACE PRIOR TO 1994 (WHEN PETROLEUM
OPERATIONS CEASED). SHADED ELEMENTS HAVE
BEEN DEMOLISHED OR DISMANTLED.
2. FIRE SCHOOL OPERATIONS WERE RELOCATED TO
THE RICHMOND REFINERY IN THE 1970'S.
3. THE PUMP HOUSE BUILDINGS WERE DEMOLISHED
AND REMOVED IN THE LATE 1990'S.
REFERENCE:
1. AERIAL PHOTOGRAPH BY CENTRAL COAST AERIAL MAPPING,
DATED MARCH 2, 2007.
2. TOPOGRAPHIC CONTOURS AND FEATURES PROVIDED BY EDA,
DATED JULY 2007.
FFTA-8
FFTA-6
FFTA-4
FFTA-5
FFTA-7
FFTA-3
FFTA-1
FFTA-2
GAS
GASOLINE
PROPOSED SOIL SAMPLE LOCATION
FIGURE
3
CHEVRON SAN LUIS OBISPO TANK FARMSAN LUIS OBISPO, CALIFORNIA
REMEDIAL ACTION PLAN
SAN LUIS OBISPO TANK FARM
NORTHWEST OPERATIONS AREA -
FEATURES AND PROPOSED SOIL
SAMPLING POINTS
FFTA-9
FIGURE
NORTHWEST OPERATIONS AREA - FEATURES
AND PROPOSED SOIL SAMPLING POINTS
FORMER CHEVRON SAN LUIS OBISPO TANK
FARM SAN LUIS OBISPO, CALIFORNIA
4
==!
==!
==!
==!
==!
==!
!
!
!!
!
!
!
!
!
!
!
!!!!
!!!
!
!
==!
==!
==!
==!!!!Airport Stormwater Outlet #6
Airport Outfall #6
Runway 11-29
VAP-7
SED-8/SW-8
120'VAP-9
80542 55538 55536 55534
80544 805465552655524
80548526
AST destroyed in
1926 fire, not rebuilt
522 AcaciaCreekBG-10
SED-5/SW-5
VAP-5
BG-9
BG-8
BG-7
SED-4/SW-4
BG-6
BG-5BG-4SED-3/SW-3BG-3BG-2
VAP-6
SED-2/SW-2
BG-1
SED-6/SW-6
SED-7/SW-7
VAP-11
VAP-10
150'140'130'VAP-1
VAP-2
VAP-3
VAP-4
VAP-13
BG-11
VAP-8
VAP-12
SED-9/SW-9
SW-1 WestForkTankFarm
C
r
e
ekT a n k F arm C reekEastFor k T a n k FarmCreek
E a s t F o r k S a n L u i s O b i s p o C re e k
Former
Recycling
Center
Reservoir 5
Reservoir 6
Reservoir 7 Reservoir 3
Reservoir 2
Reservoir 4 35°15'0"N35°14'55"N35°14'50"N35°14'45"N35°14'40"N35°14'35"N35°14'30"N35°14'25"N35°15'0"N35°14'55"N35°14'50"N35°14'45"N35°14'40"N35°14'35"N35°14'30"N35°14'25"N35°14'20"N120°38'50"W120°38'55"W120°39'0"W120°39'5"W120°39'10"W120°39'15"W120°39'20"W120°39'25"W120°39'30"W120°39'35"W120°39'40"W120°39'45"W120°39'50"W120°39'55"W120°40'0"W
120°38'50"W120°38'55"W120°39'0"W120°39'5"W120°39'10"W120°39'15"W120°39'20"W120°39'25"W120°39'30"W120°39'35"W120°39'40"W120°39'45"W120°39'50"W120°39'55"W
0 500 1,000
SCALE IN FEETI
PROPOSED SAMPLING LOCATIONS
User Name: ski01076 DATE: 2/8/2024 12:58 PMPATH: T:\_ENV\Chevron_PFAS_SLO_Tank_Farm\MXD\2023\Chevron_PFAS_SLO_Tank_Farm_2023.aprxFIGURE
5
Legend==!Proposed VAP/HPT to Bedrock Interface + 20 feet
!Proposed Sediment and Surface Water Sampling
Locations
!Proposed Background Soil Sample Location
!Proposed VAP/HPT to Bedrock Interface
Groundwater Contours
Direction of Groundwater Flow*
Buildings
Site Boundary
Current Stream Channel
Former Stream Channel
Former Aboveground Storage Tank
Former Tank (Water Tank)
Former Fire Training Area
NOTES:
* = GSI Water Solutions, Inc. 2022. San Luis
Obispo Valley Groundwater Basin Annual
Report (Water Years 2020-2021). San
Luis Obispo Basin Groundwater Sustainability
Committee and the Groundwater Sustainability
Agencies. March 24.
FORMER CHEVRON SAN LUIS OBISPO TANK FARM
SAN LUIS OBISPO, CALIFORNIA
35°16'0"N35°15'30"N35°15'0"N35°14'30"N35°14'0"N35°13'30"N35°15'30"N35°15'0"N35°14'30"N35°14'0"N35°13'30"N120°36'30"W120°37'0"W120°37'30"W120°38'0"W120°38'30"W120°39'0"W120°39'30"W120°40'0"W120°40'30"W120°41'0"W120°41'30"W120°42'0"W120°42'30"W
120°36'30"W120°37'0"W120°37'30"W120°38'0"W120°38'30"W120°39'0"W120°39'30"W120°40'0"W120°40'30"W120°41'0"W120°41'30"W120°42'0"W120°42'30"W
0 2,200 4,400
SCALE IN FEET
I POTENTIAL PFAS SOURCE
LOCATIONS User Name: ski01076 DATE: 1/24/2024 11:58 AMPATH: T:\_ENV\Chevron_PFAS_SLO_Tank_Farm\MXD\2023\Chevron_PFAS_SLO_Tank_Farm_2023.aprxFIGURE
6
Legend
POTENTIAL PFAS SOURCE LOCATIONS
NATIONAL HYDROGRAPHY DATASET
FLOWLINE AND DIRECTION
PROJECT BOUNDARY
1 MILE BUFFER
0.25 MILE BUFFER
APPROXIMATE LOCATIONS OF FEATURES OF
NOTE
SAN LUIS OBISPO REGIONAL AIRPORT
FORMER CHEVRON SAN LUIS OBISPO TANK
FARM SAN LUIS OBISPO, CALIFORNIA
Response to Regional Board's Comments Provided in
2023 Letter
Attachment A
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 1
# Regional Board Comment Response
General Comments
1. The Central Coast Water Board provided further description of those
requirements in its December 2022 Letter, which included:
The need to determine potential for transport and fate of PFAS from
the Former Fire Training Area (FFTA) in the Northwest Operations
area, per the “Requirement for a Workplan Addendum”, bullet three,
which states, “Thus, investigation of native soil, sediment, and
groundwater is needed. PFAS transport from the Northwest
Operations area potentially occurred by (1) direct infiltration to
groundwater in the source areas and/or (2) overland flow to the East
Tank Farm Creek drainage area bisected by Tank Farm Road with
recharge to groundwater along its flow path.”
A proposed schedule for site-wide PFAS investigation per the
“Workplan Addendum Implementation Schedule”, which states, “The
workplan addendum must also include an implementation schedule for
an offsite investigation commensurate with the investigation findings
for the fire training area, and a proposed schedule for a site-wide
PFAS investigation.” The scope of work partially responds to the first
requirement of the implementation schedule, while the requirement for
a schedule for the site-wide investigation remains outstanding.
The Revised Supplemental Work Plan has been modified to
include all requested media (soil, groundwater, and sediment)
be sampled as part of the proposed scope of work in one phase.
Additional groundwater, soil, sediment, and surface water
sampling points have been added to assess potential transport
of PFAS from the Northwest Operations Area as requested by
the Regional Board. The phasing of different sample media
collection (i.e., soils, then groundwater, followed by sediment)
has been removed from the Revised Supplemental Work Plan’s
scope of work. A proposed schedule has been included as
Section 6 of the Revised Supplemental Work Plan. A meeting
was held between members of the Regional Board, CEMC, and
Arcadis in November 2023. At this meeting it was agreed that
the immediate next phase of work should be focused on the
FFTA, and that conversations around scheduling of the site-wide
investigation will continue following evaluation of the impending
FFTA investigation.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 2
# Regional Board Comment Response
2. The Central Coast Water Board acknowledges the proposed stepwise
approach in the Supplemental Work Plan; however, the scope of work
presented requires clarification and rescoping to focus the first phase of
investigation on the Northwest Operations Area FFTA activities. For example,
some of the proposed soil and sediment sampling shown on Figure 7 do not
address the FFTA in the Northwest Operations Area regarding source
identification. Specifically, the proposed soil and sediment sampling locations
BG-1 to BG-10 and SED-1 to SED-5, respectively, do not respond to the two-
phased approach as described in the Central Coast Water Board’s December
2022 Letter for the FFTA in the Northwest Operations Areas. These sample
locations would be more appropriately directed toward filling data gaps in the
conceptual site model (CSM) in the event a source area is identified in the
Northwest Operations Area for the FFTA and related activities, as detailed
further herein.
See Response to Comment (RTC) #1. As discussed in the
Original, and Revised Supplemental Work Plan text, various
sampling locations have been selected to help establish what
contamination, if any, may be attributable to offsite sources.
The original Order requested work be performed to determine
the “extent of PFAS suspected to be at and emanating from
the SLO Tank Farm.” These background/ambient locations
will aid in determining what measured PFAS may be
emanating from the FFTA, and what may instead be
attributable to offsite source(s).
3. The Central Coast Water Board’s December 2022 Letter emphasizes the need
to investigate the potential for PFAS to migrate to groundwater from the
Northwest Operations Area FFTA due to the presence of the off-site supply
wells identified to the west of the property in the westerly groundwater flow
direction from the Site. Central Coast Water Board staff, in numerous meetings
and teleconferences with CEMC and their representatives, identified the
channel and basin area south of Tank Farm Road along Tank Farm Creek,
and the area west of Tank Farm Creek, as essential to the first phase of
investigation efforts with the objective of addressing potential sources of PFAS
to the off-site supply wells. This investigation is missing from the Supplemental
Work Plan and must be included as part of a revised scope of work.
The Revised Supplemental Work Plan has been modified to
include an additional groundwater sampling point (VAP-10)
downgradient of the FFTA, south of Tank Farm Road, west of
Tank Farm Creek, and adjacent to the off-site supply wells.
Three sediment/surface water sampling locations (SED-6
through SED-8) have been added to Tank Farm Creek,
downstream of the FFTA (Figure 5).
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 3
# Regional Board Comment Response
4. The scope of work requires reframing around investigation efforts tailored to
source identification that is more general in scope, as opposed to the proposed
discrete level of data collection currently proposed for targeted aquifer profiling
across thin complex interbed layers for lithology analyses, and the multi-
sampling approach across thinly-interbedded groundwater zones. Currently
available characterization information including boring logs, groundwater
elevations and flow directions, monitoring for constituents of concern, etc. from
Union Oil Company of California’ years of Site investigation should be
integrated, and presented to illustrate the understanding of Site conditions and
support proposed sampling locations.
The Revised Supplemental Work Plan has been modified to
include additional sampling points around the FFTA for the
purpose of source determination. The dataset previously
developed for groundwater characterization at the Site would
benefit from the addition of aquifer profiling as described in
the workplan. This approach was discussed and agreed upon
between members of the Regional Board, CEMC, and Arcadis
in a November 2023 meeting. Specifically, the Regional Board
stated “your vertical investigation is suitable, though needs to
be expanded horizontally.”
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 4
# Regional Board Comment Response
5. The hydrogeologic investigation methods proposed in the Supplemental Work
Plan are applicable once primary source zones have been identified.
Afterward, the primary data quality objectives (DQOs) should shift to a
delineation of the primary source areas for transport and fate analyses toward
developing a more detailed CSM, determining risk to receptors, and
understanding and developing feasibility analyses for control and cleanup
options. The Central Coast Water Board does not concur with CEMC’s
proposed requesting of a “no further action” (NFA) determination between
each phase of the investigation and will evaluate an NFA determination when
the approved scope of work is completed.
See RTC #4. All proposed pathways to request NFA have
been removed from the Revised Supplemental Work Plan.
The intent of the Revised Supplemental Work Plan is to
definitively determine the presence or absence of targeted
PFAS in soil, groundwater, sediment, and surface water that
may be emanating from the FFTA. Due to the presence of
multiple known and suspected offsite sources, data collected
at and downgradient/downstream of the FFTA will be
compared to investigation data collected along upgradient and
upstream locations. In addition, analyte-specific abundance
profiles or source “signature” comparisons will provide
valuable insight as to what, if any, PFAS contamination may
be attributable to the FFTA. The hydrogeologic methods are
proposed to fulfill the additional objectives including, a) the
identification of groundwater pathways downgradient of the
FFTA , b) evaluating vertical conductivity to deeper
groundwater bearing zones (i.e., the groundwater zones the
offsite water supply wells are screened in), and c)
identification of potential groundwater pathways across and
onto the Site.
6. Section 3, 3.1, Attachment A, Quality Assurance Project Plan (QAPP), et. Al.:
Remove the requests for NFA as intervening steps for the investigation of soil,
sediment, and groundwater. Central Coast Water Board staff requires revising
the scope of work throughout the various sections of the work plan to present a
baseline sequencing approach that starts with the Northwest Operations Area,
then a site wide evaluation.
All proposed pathways to request NFA have been removed from
the Revised Supplemental Work Plan.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 5
# Regional Board Comment Response
7. Section 3, 3.1 and 3.2: Proposed expanded soil and groundwater
investigations within the Northwest Operations area related to the FFTA, as
only five (5) soil borings locations are currently proposed. Additional sampling
locations are needed to account for historic operational variabilities and
uncertainties, as cited in the Supplemental Work Plan, in the areas
surrounding burn trench. Examples include activities such as nozzle testing for
fire suppression mixture optimization for aqueous film forming foam (AFFF) not
directly deployed to extinguishing fires in the fire trench noted in the
Supplemental Work Plan; nozzle cleaning post AFFF deployments, chemical
storage and mixing areas and appurtenances and related out-buildings; among
other related structures and activities. Toward this effort, consider utilizing and
presenting larger scale overlays of historical aerial photographs, former
operations schematics (such as those in the 2015 RAP) for the Northwest
Operations area help to inform a proposed expanded investigation for the
above partial list of considerations for further developing a revised scope of
work.
Four (4) soil boring locations have been added to scope of work.
Nine (9) soil boring locations are proposed at/near the FFTA.
These locations have been selected using historic infrastructure
maps of the FFTA as identified in Figure 4 and new information
including an 1976 historic fire location.
As explained in the text, no AFFF use (and hence, no AFFF
nozzle testing or cleaning areas) were identified on site.
Instead, appropriate investigation of the known FFTA and
infrastructure is proposed.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 6
# Regional Board Comment Response
8. Section 3, 3.2: Similar to the previous comment, a groundwater investigation is
needed south of Tank Farm Road along the western site boundary. The
objectives are to assess the potential for overland flow and infiltration from
surface water to groundwater from Northwest Operations area and FFTA, to
determine the relative horizontal and vertical hydrogeologic conditions for
developing transport and fate conditions to inform the CSM relative to the off-
site supply wells to the west, and to determine potential impacts from industrial
activities west of the property, as indicated, in part, in section 1.5 of the
Supplemental Work Plan. Because more than one groundwater sampling
event will be necessary to confirm ongoing chemical and hydrogeologic
conditions at the Site, consider installing permanent (vs. temporary)
groundwater monitoring wells.
One (1) groundwater sampling location has been added south of
the FFTA and along the western Site boundary. Monitoring Well
MW-41 is south of Tank Farm Road, west of Tank Farm Creek,
and near the western property boundary. MW-41 was sampled
as part of the 2021 investigation activities. Results were below
California Department of Drinking Water response levels for
regulated compounds. Overland flow from the FFTA will also be
addressed by the addition of three (3) sediment sampling
locations within Tank Farm Creek and its westernmost tributary.
Furthermore, a stormwater sample has been proposed to collect
discharge from the adjacent San Luis Auto Salvage Yard, which
maintains an industrial activity general permit to discharge storm
water. The permitted stormwater sampling point is at the
property boundary, adjacent to the storm channel flood control
feature on the SLO Tank Farm property.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 7
# Regional Board Comment Response
9. Section 3, 3.3: Propose a scope of work for sediment investigation for the
Northwest Operations Area FFTA and south of Tank Farm Road along current
and historic drainages related to runoff from the FFTA as potential routes of
overland transport and fate for PFAS from the Northwest Operations Aera
FFTA. The need for the sediment sampling is consistent with the requirements
of the Central Coast Water Board’s 2020 Order and December 2022 Letter,
and previous discussions involving Central Coast Water Board staff, CEMC
representatives, and ARCADIS, technical representatives for CEMC. Also,
during numerous discussions with CEMC and ARCADIS staff, Central Coast
Water Board staff conveyed the requirement for a proposed scope of work for
investigating sediment in the drainages flowing from the FFTA to current and
previous drainage ways, both proximal and distal to the Northwest Operations
Area. The intent of the required scope of work for a sediment investigation
serves the dual objective of assessing the relative presence/absence of PFAS
and their potential for infiltration to groundwater in the channel and basin areas
south of Tank Farm Road and along the western site boundary related to
FFTA in the Northwest Operations Area.
Three (3) sediment sampling locations, within Tank Farm Creek
and its westernmost tributary, have been added to the Revised
Supplemental Workplan (Figure 5).
10. Attachment F, Portable Document Format (PDF) page 141, section 3: Please
note that approval is required for injection of fluorescein dye to groundwater
pursuant to Central Coast Water Board Order R3-2019-0089, General Waiver
for Specific Types of Discharges, dated September 20, 2019 (General
Waiver).8 If fluorescein dye or other tracer dyes are proposed for use, the
revised Supplemental Work Plan scope or work must expressly indicate that
such injections with will meet the conditions of Order R3-2019-0089,
Attachment A, Section B. The potential use of fluorescein dye would be
considered as a component of the overall site investigation and cleanup effort
and could be performed under the existing General Waiver with modifications
for compliance with the conditions for injections to groundwater.
Any proposed injection will be used in accordance with Central
Coast Water Board Order R3-2019-0089. The Revised
Supplemental Workplan has been updated to include the
assurance that any use of fluorescein dye will be in accordance
with Central Coast Water Board Order R3-2019-0089.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 8
# Regional Board Comment Response
Specific Comments
11. Section 1.2 and 2, groundwater hydrology: Conclusions regarding vertical
communication between groundwater-bearing zones being “unlikely” must be
further assessed on a macro scale (vs. micro scale as currently proposed).
The March 31, 2015 Final Remedial Action (2015 RAP) Plan, PDF page 51,
section 6.6, and PDF page 92, Figure 3, respectively, describe and illustrate
12-inch large diameter supply wells in the Northwest Operations Area with
notations indicating “abandon.” Description of the histories for these wells in
the 2015 RAP indicates documentation is not available for their historical uses,
pumping rates, construction information for the presence or absence of
annular seals and depths, number and depth of screened intervals, total well
depths; and whether proper abandonment was performed prior the
implementation of the remedy. As part of the revised Supplemental Work Plan,
include a discussion of the final determination regarding location efforts for
proper abandonment of these wells as described in section 6.6 of the 2015
RAP, and provide a related description as part of the CSM, consideration of
potential vertical preferential transport of PFAS between groundwater-bearing
units under theoretical pumping conditions and passive scenarios for non-
pumping conditions.
The March 31, 2015 Final Remedial Action Plan (2015 RAP)
identified two (2) historical water wells in the Northwest
Operations Area. The approximate locations of the wells were
unable to be verified and “It is likely that the wells were
abandoned many years ago and any other record of them has
long since been lost” (Trihydro 2015). Historical records and well
completion reports were reviewed to identify the status of the
12-inch- diameter supply wells in the Northwest Operations
Area. Additionally, geophysical subsurface investigations for
these wells were completed as part of the Northwest Operations
Area excavation and capping effort. Neither the historical
records review nor subsurface investigations identified the
presence or abandonment of additional supply wells.
12. Section 3.1, Soil Investigation: Further evaluation and explanation is required
for potential biases of laboratory analytical results during sample preparation
involving non-aqueous phase liquid (NAPL) occurrences for soil and
groundwater. The response must include a discussion of data reliability and
confidence relative to the DQOs for achieving data representative of Site
conditions for evaluation and decision-making purposes. Part of the response
must also include how laboratory sample preparation and analytical methods
may account for biases depending on utilization of various internal procedures.
NAPL extraction will not be performed on soil and groundwater
samples unless the presence of significant amounts of NAPL
prohibit analysis of the sample. Whole samples will be analyzed
so that an accurate representation of soil or groundwater PFAS
concentrations will be identified. This whole-sample analysis
methodology aligns with the primary data quality objective,
“…determine the presence or absence of PFAS in soil,
groundwater, and sediment.”
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 9
# Regional Board Comment Response
13. Section 3.2, Groundwater Investigation: Specify the rationale for the selected
sampling intervals and depths. Attachment F indicates 3- to 5-foot intervals for
more thinly bedded geologic conditions, conditions that are likely to be
encountered at the site, whereas the Supplemental Work Plan scope of work
indicates 5- to 10-foot internals. Given the relatively shallow depth to
groundwater and complex hydrogeologic conditions that occur across the Site,
implementation of the more frequent sampling internals appears appropriate
for determining Site characteristics for transport and fate flow paths related to
the targeted groundwater sampling and development of the CSM. Also refer to
the above General Comment regarding the proposed approach and
methodologies for groundwater sampling scope and scale related to DQOs for
source investigation.
Attachment F of the 2023 Supplemental Work Plan is a
Technical Guidance Instruction (TGI) for Vertical Aquifer Profile
(VAP) Sampling. These TGI documents are written to provide
general instruction for activity implementation across a variety of
site conditions. While the Site geologic conditions are thinly
bedded, a 5- to 10-foot interval is adequate to assess
groundwater contaminant concentrations. Ultimately, sample
intervals will be selected real time during the investigation based
on the HPT data to identify zones of higher permeability based
on observed conditions at each boring.
14. Section 3.2: PDF page 15, continued paragraph at top of page: Central Coast
Water Board staff recommends collecting soil samples for PFAS analyses
along with the proposed collection of soil cores for geophysical properties for
the objective of determining the presence or absence of targeted PFAS.
Soil samples for geophysical properties analysis must be
collected as intact cores to develop a comprehensive
understanding of groundwater hydrogeology and vertical
connectivity. As a result, collecting soil samples for PFAS
analytes along with the proposed collection of soil cores would
require an additional borehole for each location. If AFFF was
used at the FFTA indications of its use will be present in the soil
samples scoped for investigation. Collecting soil samples at the
VAP/HPT locations near the FFTA would therefore be
redundant. For background VAP/HPT locations Arcadis is
proposing standalone soil samples around the perimeter of the
property (Figure 5).
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 10
# Regional Board Comment Response
15. Section 4, PDF page 21, second paragraph: Clarify use and application of
tracer dye, if any. The hydraulic profiling method described earlier in the
Supplemental Work Plan scope of work does not indicate that use of a tracer
dye for vertical aquifer profiling (VAP) is needed to determine groundwater
sampling zones that will already be identified via use of the hydraulic profiling
tool (HPT). Given that the HPT locations are posed as part of a paired
geophysical investigation approach for optimizing the proposed groundwater
sampling, define the conditions that may indicate use of a tracer.
Tracer dye would only be used if drilling fluids (e.g., water) are
needed during the drilling of VAP/HPT boreholes based on
encountered drilling conditions. Typically, when groundwater
sampling is performed during drilling, the purge volume to be
removed is at least as much as was lost during drilling.
However, accurately determining the volume of water lost to the
formation or specific intervals within the borehole is not always
feasible or possible. Using tracer dye in any drilling fluids
applied to the subsurface will be used to visually confirm when
unimpacted native groundwater enters the borehole. The tracer
dye would be used to identify the dilution of groundwater by
drilling fluids and if correction factors/groundwater purging is
required to collect a representative sample. Note that the use of
water (and resulting tracer dye) during drilling operations is not
expected. Any proposed injection will be used in accordance
with Central Coast Water Board Order R3-2019-0089. If
possible, drilling for the VAP borings will be conducted without
the use of drilling water.
16. Section 4, PDF page 21, third paragraph: Provide a description for including
PFAS sampling as part of the sampling for the soil cores (see previous related
comment), as the soil core recovery methodology may allow, or if feasible.
See RTC #14. Soil core recovery as scoped for geophysical
analysis will not provide suitable volume for PFAS analysis
without the addition of additional test boreholes.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 11
# Regional Board Comment Response
17. Section 4, PDF page 22, first paragraph: Describe the criteria used to
determine whether soil core retrieval will be utilized utilizing the proposed
direct-push advancement tool, and how the decision whether to collect the
cores aligns with the overall data collection objectives toward Site
characterization.
This text has been removed from the Revised Supplemental
Work Plan. HPT data will be used to identify target
groundwater sampling intervals. The collection of soil cores
for PFAS analysis at groundwater investigation locations is
not planned as part of the revised work scope. Soil
investigation locations are scoped separately (Figure 4 and
Figure 5).
The collection of soil cores directly for geophysical properties
correlates with the data objectives toward Site characterization
and to fill the data gap of vertical conductivity to deeper
groundwater bearing units. The collection of soil cores will be
used in conjunction with the HPT data to establish detailed
modeling inputs for groundwater flow at the FFTA.
18. Section 4, PDF page 22, second paragraph: See prior comment regarding use
of tracer dye and requirements for compliance with the conditions of the
General Waiver.
See RTC #15.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 12
# Regional Board Comment Response
19. Section 5, Table 4. PFAS Analyte List: Constituent list needs to match updated
constituent list in the State Water Resources Control Board’s (State Water
Board) December 6, 2022, “Target Reporting Limits” table, at a minimum, and
reporting of all resultant laboratory reportable PFAS is required. The Table 4
list also differs from the list in Appendix E, Table 3a. Explain the reasons for
the difference. Please also note the reporting limits and provide consistency
throughout the work plan and confirm laboratory capabilities for analyses of the
PFAS listed in the State Water Board’s PFAS Target Reporting Limits table.
The constituent list identified in Table 4 has been updated to
align with the State Water Board’s December 6, 2022 “Target
Reporting Limits” table, which lists criteria for 43 PFAS
compounds. Eurofins Lancaster Laboratories method
detection and reporting limit capabilities have been added to
Table 4 for the requested analyses. With the exception of
three compounds, draft analytical method 1633 will be used.
The remaining three compounds (10:2 Fluorotelomer sulfonic
acid, Perfluorooctadecanoic acid, and Perfluorohexadecanoic
acid) will be analyzed by method 537.1 Modified. The
discrepancy between Table 4 and Appendix E, Table 3a, of
the original work plan was inadvertent. This comment is
acknowledged and appreciated.
20. Figure 7, Proposed Sampling Locations: As indicted in the General Comments
herein and consistent with the Central Coast Water Board’s requirements
detailed herein for the revised Supplemental Work Plan scope of work, revise
Figure 7 to illustrate sediment, soil, and groundwater sampling locations
correspondingly. Include selected locations for hydrologic profiling with
groundwater sampling to determine the potential for PFAS from on-site
sources and possible PFAS from sources off-site. Sampling locations that
focus on the northwest corner of the Site property south of Tank Farm Road
and within the East Tank Farm Creek drainage area corridor, must be
included.
Figure 5 has been updated to include sampling locations
south of Tank Farm Road and within the East Tank Farm
Creek drainage area. An additional figure, Figure 4, has been
included to show the focus of soil sampling at the FFTA. The
text of the Revised Supplemental Work Plan provides
rationale for sample location selection.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 13
# Regional Board Comment Response
21. Figure 7, Proposed Sampling Locations: Soil sampling locations BG-6 through
BG-10 appear to be selected to evaluate if off-site PFAS sources are coming
onto the Site. However, not all potential sources on the Site are being
evaluated with limited (only five) soil samples proposed for the FFTA, no soil
sample locations proposed south of the FFTA, and no soil sample locations
are proposed on or near the Site’s Former Recycling Center.
Soil sampling locations BG-1 through BG-10 (and now BG-11)
depicted on Figure 7 of the Supplemental Work Plan (now
Figure 5 of the Revised Supplemental Work Plan) have been
selected to evaluate background/ambient PFAS
concentrations at the perimeter of the Site and outside of
historic fire training activities. Additional soil samples have
been proposed within the FFTA at locations of former
infrastructure, as shown in Figure 4. During the November
2023 meeting the Regional Board agreed that the next phase
of the investigation should be focused on the FFTA, and not
site wide (including the Former Recycling Center).
22. Figure 8, Proposed Northwest Operations Area Sampling Locations: As
indicated in the general comments herein, an expanded areal sampling is
required due to operational variabilities and uncertainties, fate and transport
considerations, and for gathering a broader data set for Site source evaluation
purposes. Sediment sampling along the unnamed tributary west of the branch
of West Fork Tank Farm Creek, and as close to the FFTA as possible and
within native sediments in the wetland areas (i.e., re-established, and
rehabilitated), to the extent feasible.
Additional soil samples have been proposed within the FFTA,
as shown in Figure 4. Sediment sampling locations have
been added along the unnamed tributary west of the branch
of West Fork Tank Farm Creek (Figure 5). Sediment
sampling locations and an additional VAP/HPT location have
been added south of the FFTA to address fate and transport
considerations (Figure 5). Furthermore, surface water
samples have also been proposed in the Revised
Supplemental Work Plan, which will be collected at areas of
sediment collection (or immediately upstream to avoid
sediment disturbance impacts)
23. Attachment A, PDF page 42, CSM, note 2: Explain rationale for determination
that stormwater runoff from the FFTA would not have potentially caused PFAS
impacts in uncapped and un-remediated areas. Due to the potential routes of
exposure, features comprising the drainages that would have served as
conveyances for runoff from FFTA activities require investigation as part of the
revised Supplemental Work Plan.
Sediment sampling locations have been added to the drainages
downstream of the FFTA (Figure 5). VAP/HPT locations have
been added south and west of the FFTA. These additional
sampling points address fate and transport considerations from
the FFTA.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 14
# Regional Board Comment Response
24. Attachment A, PDF page 43, table column Phase I, second column Objective,
second row down: Please update this table to be part of the revised scope of
work in reference to the above comments for expanded investigation.
The scope of work provided in the Revised Supplemental Work
Plan no longer includes no-further-action decision points or
contingent-based next steps. The Technical Objective and
Conceptual Work Plan Approach Table, provided in Attachment
A in the 2023 Supplemental Work Plan, has been omitted from
the Revised Supplemental Work Plan to fulfill the request of the
Regional Board for reduced work plan file size/length.
25. Attachment A, PDF page 45, table column Phase 3, third column Method /
Rationale, second bullet: Provide explanation for the preemptive determination
as to why and how “[...]data collected will be inconclusive in establishing a
point source.” The possibilities for multiple sources, including point sources
and diffuse “hot spot” aeras must be investigated and not immediately
discounted as inconclusive in the context of the potential routes of transport
and fate due to runoff patterns from the Northwest Operations Area and FFTA.
This comment is acknowledged. The intent of the Revised
Supplemental Work Plan is to evaluate whether the FFTA was a
source of PFAS. The areas of interest will be investigated to
determine presence / absence. PFAS analyte “signatures”
observed, if detected, will be compared against upgradient
PFAS signatures to aid in CSM development regarding
determination of contamination origin sources..
26. Attachment A, PDF page 45, note 1: See prior comments regarding a
discussion of analytical biases for potential NAPL encounters and
corresponding sampling.
See RTC #12.
27. Attachment A, PDF page 46, note 1: Phased approach schedule: General
comment consistent with requirements for revising the Supplemental Work
Plan scope of work for all media as part of a stepwise investigation removing
the references to “no further action” to comply with 2020 Order per the
December 2022 Letter.
A request for no further action related to a step wise
investigation has been removed from the Revised Supplemental
Work Plan.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 15
# Regional Board Comment Response
28. Attachment B, Aerial Imagery, 1926 photo: Explain the history, ownership
history (including if Union Oil Company of California or related entities owns or
once owned this property), and operations for what appear to be 12
tank/storage structures and related features shown to the north of the present-
day Union Oil Company of California property boundary comprising the Site.
Explain how these structures may influence the findings of the investigation,
understanding of background conditions and potential influences on DQOs and
analytical results. For example, “background” soil sampling locations BG-1
through BG-5 may not be representative of background conditions as this
property was used for oil storage. Please provide any soil and/or groundwater
sampling data related to this property north of the Site. To the extent known,
please provide information about fire fighting training activities that may have
occurred in this area.
Available historical records support that Union Oil Company
owned the properties north of the San Luis Obispo Tank Farm
(SLOTF) during the time period that the tank farm facility was
being constructed. Aerial photography depicts circular “scars”
on those northern properties similar in size and orientation to
that of the secondary containment berms encircling the above
ground storage tanks operated by Union Oil at the SLOTF.
CEMCs investigation of historical records concludes that the
property was initially intended for a potential expansion of the
SLOTF facility but was never constructed or used in that
capacity. Shortly after the 1926 aerial image was taken, the
surface use of the property was changed to that of an airstrip
(Clark Field). Clark Field was replaced circa 1939 by the
present-day San Luis Obispo County Regional Airport. Over
the years, the circular “scars” gradually faded until they were
no longer visible. Between the 1930’s and the 1990’s, Union
Oil Company sold the properties. The exact divestiture date
has not been identified.
The visual presence of these circular “scars” will not influence
the findings of the SLOTF investigation and will not have an
impact on the establishment of background data or DQOs
associated with the SLOTF PFAS investigation.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 16
# Regional Board Comment Response
29. Attachment E, PDF page 78, section 4.1, fourth paragraph: Interstate
Technology and Regulatory Council’s reference for use of standards: Explain
whether the intent for citing this reference is to portend that the two contracted
laboratories follow these sample preparation procedures, especially in relation
to the use of isotopically labelled analogs for target analytes.
The ITRC reference documents were included in the 2023
Supplemental Work Plan to provide PFAS reference
information and industry-standard procedures for the
sampling and analysis of PFAS. Note that the 2023 work plan
proposed analysis by 537.1 modified whereas the revised
supplemental work plan will primarily utilize EPA Method
1633. The ITRC site characterization, sampling precaution,
and laboratory analytical method guidance documents have
not been updated to include 1633 specifics.
30. Attachment E, PDF page 120, section 11.6, fourth bullet: Confirm use of
isotopic dilutions (ID) for targeted analytes. Please change "should" to "must"
per list on State Water Board's webpage and requirements of the Department
of Defense's Quality Systems Manual 5.3, or later, for analyses utilizing IDs for
quantifying data of known quality and representativeness of Site investigation
media.
This comment is acknowledged and will be used to update the
PFAS Sampling and Analysis Guidance prepared for Chevron
Corporation. Arcadis intends to update this guidance, in the
future, to reflect the latest regulatory requirements and
guidance criteria including those provided by the State Water
Board and the Department of Defense. The guidance has
been omitted from the revised work plan submittal at the
request of the Regional Board for reduced work plan file
size/length.
31. Attachment E, PDF page 131, section 6, Procedure 6.: Please provide a
backup plan for collecting groundwater samples for potential instances where
the targeted shallow groundwater is relatively non-recoverable. Protocols
indicate allowing sufficient time for well recoveries; however, specific
alternative plans are recommended in the event of non-recoveries per the
proposed sampling procedures. Historic field observations may provide
guidance for how reliability shallow samples can be collected when accounting
for groundwater recovery time upon purging prior to sampling.
This comment is acknowledged and will be used to update the
PFAS Sampling Procedures and Low-Flow Groundwater
Purging for Monitoring Wells. Arcadis intends to update this
guidance, prior to investigation, to reflect the latest regulatory
requirements including those provided by the State Water
Board. The guidance has been omitted from the revised work
plan submittal at the request of the Regional Board for
reduced work plan file size/length.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 17
# Regional Board Comment Response
32. Attachment F, PDF page 140, section 2, third paragraph: Clarify use of a tracer
per the following comments regarding characterization methodologies.
See RTC #15.
33. Attachment F, PDF page 141, section 3, fourth paragraph: Cross-reference to
section 4, page 2 to provide rationale and clarification for VAP profiling with
tracer fluid when using prior direct push characterization with HPT technology.
With characterization using the HPT methodology preceding VAP and VAP
samples are co-located as separate but adjacent field points, explain whether
tracer dye is needed. Use of the HPT can target transmissive zones for
optimized groundwater sampling while not using drilling fluids and tracers as
part of collecting representative groundwater samples for source area
identification and assessment. Also consider that the proposed VAP methods
may be better suited to transport and fate objectives as part of subsequent
delineation strategies once potential sources have been established.
See RTC #15.
34. Attachment F, PDF page 141, section 3, fifth paragraph: See comment to
section 3.2 of the main text regarding proposed sampling intervals.
See RTC #13.
35. Attachment F, PDF page 141, section 3, fifth paragraph: Update to refer to
section 8 on PDF page 146.
This comment is acknowledged and will be used to update the
TGI – Vertical Aquifer Profile (VAP) Sampling following
discussion with Arcadis technical experts. Arcadis intends to
update this guidance, in the future, to reflect the latest
regulatory requirements including those provided by the State
Water Board. The guidance has been omitted from the
revised work plan submittal at the request of the Regional
Board for reduced work plan file size/length.
36. Attachment F, PDF page 143, section 5, fifth solid bullet, and related section
8.2.3.2, PDF page 150: Same as comment for use of a tracer and the
proposed field sampling method for separate but co-located HPT and VAP
sampling points.
See RTC #15.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 18
# Regional Board Comment Response
37. Attachment F, PDF page 148, section 8.2, second paragraph: Same as the
previous comment.
See RTC #15.
38. Attachment F, PDF page 149, section 8.2.2, second paragraph: Discrete
sampling of deeper groundwater zones is preferrable without the use of
packers, as the noted disadvantages of groundwater introduction from above
the target zone may cause false positive results for PFAS given the low
detection and reporting limits for laboratory PFAS analytical methodologies.
Clarification is needed regarding procedures to prevent potential transfers of
PFAS between variable groundwater zones.
The TGI documents are written to provide general instruction
for implementing VAP sampling across a variety of sites and
site conditions. For PFAS sites, a top-down sampling
approach (via DPT or sonic drilling) is preferred to limit
potential for cross-contamination, and a packer sampling
assembly is not planned for use at the site. With a DPT rig, an
outer casing is advanced with the screen-point sampling
device to limit the potential for cross-contamination between
sampling intervals. With a sonic rig, a push-ahead
groundwater profiler will be driven ahead of the sonic casing
into the un-disturbed formation to the prescribed depth
interval, and the sonic casing limits the potential for
groundwater introduction from above the target interval.
39. Attachment F, PDF page 155, section 11.5, last bullet: Please update to also
include the latest applicable version of the Department of Defense Quality
Systems Manual, i.e., version 5.4.
See RTC #30.
40. Attachment H, PDF page 240, QAPP Worksheet # 11, third and fourth
paragraphs: Same as prior comments requiring a description of the potential
for sample biases and how resultant data will be evaluated for determining its
representativeness to Site conditions.
See RTC #12.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 19
# Regional Board Comment Response
41. Attachment H, PDF page 241, QAPP Worksheet # 11, second full paragraph:
Describe the rationale for determining the need for performing data validation.
Main text of the Supplemental Work Plan (e.g., PDF page 25, section 5) and
other portions throughout definitively indicate procedures and process for
performing data validation and reporting, whereas the text of Worksheet # 11
suggests a discretionary approach to performing and reporting data validation.
Please also confirm whether analytical data from use of alternative analytical
protocols and methods will likewise undergo validation, such USEPA
methodologies pending approval to be consistent with the above referenced
State Water Board’s Target Reporting Limits analyte list for PFAS.
All analytical data collected for CEMC undergoes 3rd party
data validation. Arcadis and CEMC utilize Eurofins Lancaster
Labs (Eurofins) for all PFAS analysis. As analytical protocols
progress Eurofins consistently audits and validates processes
consistent with USEPA expectations.
42. Attachment H, PDF page 251, QAPP Worksheet # 15: Clarify example
Reporting Limits noted in the listings versus actual Reporting limits to be used
in comparison to those cited in the State Water Board’s Target Reporting
Limits. Please ensure consistency throughout the revised Supplemental Work
Plan.
Updated analyte reporting limits have been provided in Table
4. The QAPP within the project files has been updated to
include the revised analyte list as provided in the Revised
Supplemental Work Plan. The QAPP has been omitted from
the revised work plan submittal at the request of the Regional
Board for reduced work plan file size/length.
43. Attachment H, PDF page 253, QAPP Worksheet # 17, first paragraph: Clarify
whether the reference to Figure 2 needs to be updated to correctly reference
Figures 7 and 8.
This comment is acknowledged. The QAPP within the project
files has been updated to reference the updated figures
provided in the Revised Supplemental Work Plan. The QAPP
has been omitted from the revised work plan submittal at the
request of the Regional Board for reduced work plan file
size/length.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 20
# Regional Board Comment Response
44. Attachment H, PDF page 254, QAPP Worksheet # 17, first paragraph under
the heading “Soil Sampling”: Please reference the General Comments
regarding the required revised scope of work to an expanded areal
investigation for soil sampling due to operational variabilities and uncertainties.
This comment is acknowledged. The areal extent of soil
sampling has been expanded as previously described. The
QAPP within the project files has been updated to include the
revised scope of work provided in the Revised Supplemental
Work Plan. The QAPP has been omitted from the revised
work plan submittal at the request of the Regional Board for
reduced work plan file size/length.
45. Attachment H, PDF page 254, QAPP Worksheet # 17, second main paragraph
under the heading “Soil sampling”: See prior comments regarding the need to
explain the noted analytical variables in more detail to frame how resultant
sampling data could be affected by NAPL occurrences. Compare identified
biases with DQOs for collecting data representative of Site conditions.
See RTC #12.
46. Attachment H, PDF page 255, QAPP Worksheet #17, second paragraph under
the heading “Groundwater Investigation”: Include in the revised Supplemental
Work Plan a scope of work for step-out locations consistent with an expanded
scope of work, as detailed in the General Comments.
This comment is acknowledged. The QAPP within the project
files has been updated to include the revised scope of work
provided in the Revised Supplemental Work Plan. Step-out
locations for groundwater investigation purposes may be
identified following review and interpretation of results from
the subject Revised Supplemental Work Plan scope of work.
47. Attachment H, PDF page 256, QAPP Worksheet #17, first paragraph under the
heading “Sediment Sampling”: Include in the revised Supplemental Work Plan
a scope of work for investigation of soil and sediment to the south of Tank
Farm Road and the area west of West Tank Farm Creek consistent with the
General Comments and Specific Comments. Also, provide the rationale for
preemptively deeming data as inconclusive for wetlands and flood areas (see
Specific Comments related to the wetlands and drainages).
See RTCs #1 through #10 and RTC #25.
Central Coast Regional Water Quality Control Board Response to Comments
Rejection of Supplemental Per- and Polyfluoroalkyl Substances Sampling Work Plan
San Luis Obispo Tank Farm
Geotracker Case ID: T10000020189
San Luis Obispo, California
www.arcadis.com 21
# Regional Board Comment Response
48. Attachment A, PDF page 337, section 4 Equipment List: Please specify the
use of approved and certified/verified PFAS-free detergents for the
investigation equipment decontamination procedures.
This comment is acknowledged. Pg 90 of the Supplemental
Work Plan (Attachment E) specifies use of caution and
decontamination materials not recommended for use in PFAS
site investigations.
49. Attachment C, PDF page 381, listing of analytes: Clarify if this listing includes
the use of USEPA Method 537.1 modified, as proposed in the work plan, and
provide assurances of laboratory capabilities for analyzing and reporting for
PFAS identified in the State Water Board’s Target Reporting Limits list.
This comment is acknowledged. The QAPP within the project
files has been updated to include the latest PFAS analyte list
provided in Table 4 of the Revised Supplemental Work Plan.
The QAPP has been omitted from the revised work plan
submittal at the request of the Regional Board for reduced
work plan file size/length.
San Luis Auto Salvage Industrial Stormwater Discharge
Permit Documentation
Attachment B