DERR-2024-012348

2410 WEST CALIFORNIA AVENUE • SALT LAKE CITY, UTAH 84104
PHONE [phone]
Website: www.wasatch-environmental.com • e-Mail: [e-mail]

Ms. Eileen Brennan October 15, 2024
Department of Environmental Quality Project No.: 1241-004G
Division of Environmental Response and Remediation
195 North 1950 West
Salt Lake City, Utah 84114-4840

SUBJECT: Work Plan for Proposed Subsurface Investigation and Risk Assessment
C-40 Top Stop
1355 East Highway 40
Vernal, Utah
UST Facility No. 9000221
Release Sites: FDL and NON

Wasatch Environmental, Inc., (Wasatch) is submitting this work plan to collect soil and groundwater
samples from the C-40 Top Stop facility (Facility) located in Vernal, Utah; and to use the resulting data
along with historical data to perform a risks assessment for the Facility. This subsurface investigation and
risk assessment work is proposed in response to the Division of Environmental Response and
Remediation (DERR) letters dated May 7, 2024, regarding Corrective Action Plan (CAP) requirements for
Release Site FDL; and dated May 13, 2024, regarding subsurface investigation and reporting
requirements for Release Site NON. Undertaking this work will provide Top Stop, Wasatch, and the
DERR with additional laboratory analytical data which will form the basis for a risk assessment, and
potentially provide a path toward the risk-based regulatory closure of both of the releases at this Facility.

Utility Clearance
At least 2 business days prior to conducting any drilling, Wasatch will submit a utility clearance request
with Blue Stakes of Utah. The Blue Stakes request number will be conveyed to the drilling contractor so
that they can duplicate the utility clearance request. The drilling contractor will also be required to provide
additional utility clearance (using ground penetrating radar, magnetometer, or similar technology) at each
boring location prior to the commencement of drilling.

Drilling Methodology
A direct-push drill rig (i.e., GeoProbe 7730 or similar unit) will be used for the soil borings. Wasatch
anticipates using Direct Push Services as the drilling contractor. Tooling will be clean and
decontaminated prior to commencement of drilling and will be decontaminated again between each of the
soil boring locations.

Sampling Methodology
All sampling will be performed by Utah Certified Underground Storage Tank (UST) Soil and Groundwater
Samplers. Sampling activities will be performed by, or under the guidance of, a Utah UST Certified
Consultant. All data analysis and reporting will be performed by, or under the guidance of, a Utah UST
Certified Consultant. The proposed sampling locations are shown on Figure 1. The proposed sampling
protocol is summarized in Table 1.

Soil samples will be collected based on field observations and field screening results, and in accordance
with the proposed sampling protocol (attached as Table 1), from each direct-push boring location and
submitted for laboratory analysis. The soil samples will typically be collected from the vadose zone from
the depth(s) exhibiting the highest photoionization detector (PID) readings or from a 1-foot interval
immediately above the water table if the PID does not register a significant reading. Sample intervals will
also be selected based on historical data for the Facility, targeting intervals known to have exhibited
significant impacts during past sampling efforts.

Wasatch Environmental Inc.
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Soil samples will be obtained and dispensed into laboratory-supplied glass jars using gloved hands. The
jars will be completely filled with soil to minimize headspace within the jars. The sample jars will each be
labeled with the sample location, requested analysis, and date and time of sample collection.

Depth to groundwater measurements will be collected from monitoring wells MW-2, MW-3, MW-4, MW-5,
MW-6, MW-12, MW-13, MW-14, MW-15. Additionally, monitoring wells MW-2, MW-3 MW-4, MW-13, and
MW-14 will be checked for free product. If free product is present, the thickness of the free product will be
measured using a dual interface probe. Where absorbent socks are present in monitoring wells, the
socks will be checked and inverted or replaced as necessary.

Groundwater samples will be collected from boring locations GB-1, GB-8, GB-9, GB-10, GB-11, and GB-
12; from monitoring wells MW-2, MW-3, MW-6, MW-12, MW-13, MW-14, and MW-15; and from the oil-
water separator (OWS) in accordance with the proposed sampling protocol (attached as Table 1). The
groundwater sampling method will consist of pumping groundwater directly from the direct-push borings
and monitoring wells using a peristaltic pump. A new disposable bailer may be used for sampling the
OWS.

Groundwater samples will be obtained and dispensed into 40-milliliter (ml) capacity glass vials with
Teflon® septa caps. The vials, which will be supplied by the analytical laboratory, will contain several
drops of hydrochloric acid (HCl) as a preservative. The vials will be filled slowly until a meniscus formed
at the top of each vial, then each vial w ill be sealed with a septa cap. This procedure eliminates
headspace within the vials and, therefore, minimizes the loss of volatiles. The sample vials w ill each be
labeled with the sample location, and date and time of sample collection.

Soil and groundwater samples will be placed in a cooler with ice and transported under chain-of-custody
protocol to a Utah-certified analytical laboratory for analysis.

Laboratory Analysis
Laboratory analysis of soil and groundwater samples (except for the groundwater sample collected from
MW-5) will consist of the following analyses:
• Methyl tertiary-butyl ether (MTBE), benzene, toluene, ethylbenzene, total xylenes, and
naphthalene (MBTEXN); total petroleum hydrocarbons as gasoline-range organics (TPH-
GRO), and TPH-GRO fractionation by United States Environmental Protection Agency
(U.S. EPA) method 8260D.
• Total petroleum hydrocarbons as diesel-range organics (TPH-DRO) with silica gel
treatment by U.S. EPA method 8015M.
• TPH-DRO fractionation by U.S. EPA method 8270E.
Laboratory analysis of the groundwater sample collected from monitoring well MW-5 will consist of the
following analyses:
• MBTEXN and TPH-GRO by U.S. EPA method 8260D (no fractionation analysis); and
• TPH-DRO with silica gel treatment by U.S. EPA method 8015M (no fractionation
analysis).
All laboratory analyses will be performed by a laboratory certified by the State of Utah. Wasatch
anticipates using Chemtech-Ford Laboratories as the analytical laboratory.

Risk Assessment
A Utah Risk-Based Corrective Action (RBCA) Tier 2 risk assessment will be completed using both
historical data and the data obtained from this subsurface investigation. While Wasatch anticipates that
some residual petroleum hydrocarbon contamination remains at the Facility, the risk assessment will

Wasatch Environmental Inc.
Page 3
provide clarity regarding the level of risk the residual contamination presents to human health and the
environment, and may support the risk-based regulatory closure of the releases at the Facility.

Reporting
At the completion of the work, a report presenting the results of the work will be prepared and submitted
to DERR. The risk assessment will be included as an appendix to the report.

Sincerely,

WASATCH ENVIRONMENTAL, INC.
Michael S. Cronin, P.G.
Senior Project Geologist and Senior Project Manager
Utah UST Certified Consultant #CC 0232

Figures: Figure 1 – Proposed Sample Location Map
Table 1 – Proposed Sampling Protocol

FIGURE 1DATE: 8/13/2024PROJECT NO.: 1241-004GEnvironmental Science and Engineering
H
i
g
h
w
a
y

4
0
500 South
Diesel
Dispensers
Top
Stop
Canopy &
Gasoline
Dispensers
Propane
AST
MW-3
Fuel
ASTs
Pro
d
u
c
t

L
i
n
e
s
PROPOSED SAMPLE LOCATION MAP
Top Stop C40
Vernal, Utah
MW-6
MW-7
(not found)
MW-5
MW-14
MW-4
MW-13
MW-2
MW-12
MW-1
MW-15
Drain
Sump
D
r
a
i
n
a
g
e

P
i
p
e
P
V
C

D
r
a
i
n
a
g
e

P
i
p
e
?
Pow
e
r

L
i
n
e
Oil/water
Separator
W
a
t
e
r

L
i
n
e
Gas Line
Sewer Line
Manhole
Scale: 1” equals
approximately 50’
Monitoring Well Location
Proposed Geoprobe Boring
Location
Sew
e
r
Lin
e
GB-1
GB-2
GB-3
GB-4
GB-5 GB-6
GB-7
GB-8
GB-9GB-10
GB-11
GB-12
Table 1 - Proposed Sampling Protocol
Media Sampled
Groundwater Soil
GB-1 X X 1 Collection of current soil and groundwater data from missing well location MW-7 to evaluate downgradient extent of impacts
GB-2 X 1 Collection of current soil data adjacent to well MW-13 (impacted depth was 5 - 8 feet bgs)
GB-3 X 1 Collection of current soil data adjacent to well MW-14 (impacted depth was 2 - 8 feet bgs)
GB-4 X 1 Collection of current soil data adjacent to well MW-2 (impacted depth was 2 - 6 feet bgs)
GB-5 X 1 Collection of current soil data adjacent to well MW-12 (impacted depth was 2 - 6 feet bgs)
GB-6 X 1 Collection of current soil data adjacent to well MW-15 (impacted depth was 3 - 8 feet bgs)
GB-7 X 4 Collection of current soil data from multiple depths adjacent to well MW-3 to evaluate nature and extent of impacts in the AST area
GB-8 X X 4 Collection of current soil data from multiple depths and groundwater data to evaluate nature and extent of impacts in the AST area
GB-9 X X 4 Collection of current soil data from multiple depths and groundwater data to evaluate nature and extent of impacts in the AST area
GB-10 X X 4 Collection of current soil data from multiple depths and groundwater data to evaluate nature and extent of impacts in the AST area
GB-11 X X 4 Collection of current soil data from multiple depths and groundwater data to evaluate nature and extent of impacts in the AST area
GB-12 X X 4 Collection of current soil data from multiple depths and groundwater data to evaluate nature and extent of impacts in the AST area
MW-2 X X X Collection of current groundwater data for fractionation (use with soil data from Geoprobe boring GB-4)
MW-3 X X X Collection of current groundwater data for fractionation (use with soil data from Geoprobe boring GB-7)
MW-4 X X No sample, just depth to groundwater measurement, product thickness measurement, and sock check
MW-5 X X Collection of current groundwater data for routine monitoring (no soil sampling and no fractionation)
MW-6 X X Collection of current groundwater data for fractionation (no soil sampling)
MW-12 X X Collection of current groundwater data for fractionation (use with soil data from Geoprobe boring GB-5)
MW-13 X X X Collection of current groundwater data for fractionation (use with soil data from Geoprobe boring GB-2)
MW-14 X X X Collection of current groundwater data for fractionation (use with soil data from Geoprobe boring GB-3)
MW-15 X X Collection of current groundwater data for fractionation (use with soil data from Geoprobe boring GB-6)
OWS Effluent X Collection of current groundwater data for fractionation
Notes:
Each Geoprobe boring will extend to a depth of 8 to 10 feet bgs.
Sample locations GB-1, GB-2, GB-3, GB-4, GB-5, and GB-6 include collecting one soil sample from the most impacted zone in each boring based on field screening, field observations, and prior data.
Sample locations GB-7, GB-8, GB-9, GB-10, GB-11, and GB-12 include collecting soil samples from up to 3 impacted depth intervals, and a clean sample from the bottom of each boring.
No sampling at MW-4, just depth to groundwater and free product check.
No fractionation analysis at MW-5, just our normal MBTEXN, TPH-DRO, and TPH-GRO.
Perform normal service of OWS using Rhett Trucking.
Anlytical Methods:
TPH-GRO/TPH-GRO Fractionation/MBTEXN by 8260D - all soil and groundwater samples except MW-5.
TPH-DRO with silica gel treatment by 8015M - all soil and groundwater samples except MW-5.
TPH-DRO Fractionation by 8015M - all soil and groundwater samples except MW-5.
TPH-GRO and MBTEXN by 8260D - MW-5 groundwater sample only.
TPH-DRO by 8015M - MW-5 Groundwater sample only.
Number
of Soil
Sample
Intervals
Sample
Location Sampling Rationale
Measure
Depth to
Groundwater
Measure
Product
Thickness and
Check Sock