DERR-2024-010970

215 South State Street, Suite 500
Salt Lake City, UT 84111
PH 801.853.8185
FAX [phone]
www.geosyntec.com
September 9, 2024 (updated
September 19, 2024)
Ms. Allison Stanley
Utah Department of Environmental Quality
Division of Environmental Response and Remediation
195 North 1950 West
Salt Lake City, Utah
Subject: Site Characterization Work Plan Addendum
Paxton Development, Voluntary Cleanup Site #C-129
203 to225 West Paxton Avenue
Salt Lake City, Utah
Dear Ms. Stanley:
On behalf of Paxton Project, LLC (Paxton), Geosyntec Consultants (Geosyntec) has prepared this
Site Characterization Work Plan Addendum (SCWP Addendum) for the Paxton residential
development project located from 203 to 225 West Paxton Avenue in Salt Lake City, Utah (Site).
The characterization and remediation of the Site are being conducted under the DERR Voluntary
Cleanup Program (Voluntary Cleanup Site #C-129).
This Addendum supplements the initial Site Characterization Work Plan (SCWP) that was
prepared for the project and approved by the Utah Department of Environmental Quality (UDEQ),
Division of Environmental Response and Remediation (DERR) on July 16, 2024. This SCWP
Addendum presents the preliminary soil data and proposed additional soil sampling activities.
These additional activities are considered “opportunistic samples” for further characterization as
described in the SCWP. The laboratory reports, validation reports, etc. will be provided with the
final site characterization report for the project, which will present all of the characterization data
for the Site.
PRELIMINARY SOIL SAMPLE DATA
In accordance with the SCWP, surface and subsurface soil samples were collected from
representative areas within the former storage yard at the Site to characterize potential impacts
from the previous storage of vehicles, equipment and potential incidental spills/or leaks of
petroleum products. Samples were focused in the areas where exposed soil is present and not where
impervious surfaces or structures currently exists. Initial soil samples were collected on July 16,
2024. The samples were analyzed for metals, petroleum constituents, volatile organic compounds
(VOCs) using the methods specified in the SCWP and associated Quality Assurance Project Plan
Ms. Allison Stanley
September 9, 2024
Page 2

(QAPP). The location of the initial samples is provided on Figure 1. Preliminary draft data
analytical results from the samples are summarized on Table 1 (detected compounds only).
In accordance with the SCWP and QAPP, the preliminary results have been screened against the
EPA residential Regional Screening Levels (RSLs) for residential soil and the DERR Initial
Screening Levels (ISLs) for underground storage tanks sites. Additionally, metals concentrations
were screened against average background soil concentrations for the conterminous United States1
to evaluate the presence of naturally occurring levels of metals in Site soils.
As shown on Table 1, concentrations exceeding Site screening levels were identified for arsenic,
lead, cadmium, total petroleum hydrocarbons – diesel range organics (TPH-DRO) and oil and
grease in one or more soil samples. All other parameters were below relevant screening levels.
Potentially elevated levels of arsenic (concentrations above the EPA RSL and typical average
background concentrations) were detected in seven of the ten locations that were sampled (S-1, S-
2, S-3, S-4, S-7, S-9 and SS-1). At locations where potentially elevated levels of arsenic were
observed, lead was also detected at concentrations above the EPA RSL at five locations (S-1, S-3,
S-4, S-7 and SS-1). Elevated levels of cadmium were also detected at one location (S-4). Detected
concentrations of TPH-DRO and/or oil and grease were detected exceeding the DERR ISLs at five
locations (S-4, S-5, S-6, S-7 and SS-1).
PROPOSED ADDITIONAL SOIL SAMPLES
Based on the initial soil sample results, additional soil samples are proposed to further characterize
both the vertical and horizontal extent of shallow impacts within the Site. Additional soil samples
will also be collected from beneath impervious surfaces.

A summary of the proposed locations is provided on Table 2, including the rational and proposed
depths for each sample. The locations of the proposed samples are also presented on Figure 2. All
samples will be collected and analyzed consistent with the soil sampling procedures and analytical
methods previously provided in the SCWP and project QAPP. At the sample locations where
exceedances have been observed, only the parameters that exceeded in the initial sample will be
analyzed. At all other locations, the full suite of analyses will be performed as detailed in the
SCWP (see Table 2).

As shown on Figure 2, many of the proposed additional samples are located in areas where
impervious surfaces are currently present (asphalt or cement). Paxton is currently working on

1 Element Concentrations in Soils and Other Surficial Materials of the Conterminous United States, U.S. Geological
Survey Professional Paper 1270, Hansford T. Shacklette and Josephine G. Boerngen
Ms. Allison Stanley
September 9, 2024
Page 3

coordinating demolition of the Site buildings and structures. During this work the asphalt and
concrete surfaces will also be removed. If the demolition work is not completed prior to sampling,
the locations where asphalt or concrete are present will require coring to remove the existing
surface material prior to sample collection. If aggregate or bedding material is present during
boring this will also be removed to facilitate sample collection of the soil.

In addition to the supplemental soil samples described herein, it is envisioned that the soil gas
samples that were described in the SCWP will also be collected in conjunction with this sampling
event.
SCHEDULE
It is anticipated that the additional soil sampling activities will require two days to complete. We
have tentatively scheduled to conduct these activities starting on September 24, 2024.
CLOSING
Geosyntec appreciates your review of this SCWP Addendum. If you have any questions or need
additional information, please do not hesitate to contact me ([e-mail] or 801-
853-8185). Alternatively, Mr. Bruce Bastian at Paxton can be reached at 801-882-0588.
Sincerely,

Brent C. Robinson, P.E.
Senior Principal

FIGURES
J.

W
e
l
c
h
Legend
Figure
1
Initial Soil Sample Locations
203 to 225 West.
Salt Lake City, Utah
Salt Lake City, UT September 2024
Client LogoPaxton
Development
Approximate Site Boundary
Previous Soil Sample Location by AGEC (depth
sampled)
Impervious Surfaces
Initial SCWP Sample Location
GP-2 (6-7’)
MW-8 (7’)MW-4
(7’)
GP-1
(6-7’)
GP-4 (6-7’)
MW-7 (7‘)SS-2 (0-.5’)
SS-1 (0-.5’)
MW-2 (7’)
MW-3
(1-2’)
GP-5 (0-1’)
MW-6 (7’)
GP-3
(7-8’)
MW-1 (7’)
MW-10
(7’)
MW-9
(7’)
MW-5 (7’)
S-1
S-2 S-3
S-4 S-5
S-6 S-7 S-8
S-3
S-9
Initial SCWP Soil Sample Location with
exceedance of one or more criteria
SS-1
B.
S
m
i
t
h
Legend
Figure
3
Proposed Additional Shallow Soil Sample Locations
203 to 225 West.
Salt Lake City, Utah
Salt Lake City, UT September 2024
Client LogoPaxton
Development
Approximate Site Boundary
Impervious Surfaces
Initial SCWP Soil Sample Locations
SS-1
S-1
S-2
S-4 S-5
S-6 S-7 S-8
S-3
S-9
Initial SCWP Soil Sample Location with
exceedance of one or more criteria
New Soil Sample Location
S-10 S-11 S-12
S-14
S-13
S-15
Initial SCWP Soil Sample Location where
additional sample is proposed

TABLES
TABLE 1
PRELIMINARY SOIL SAMPLE SUMMARY
PAXTON DEVELOPMENT
SALT LAKE CITY, UTAH
DRAFT - DATA NOT VALIDATED
SAMPLE LOCATION S-1 (0-6)S-1 (6-12)S-2 (0-6)S-3 (0-6)S-3 (6-12)S-3 (6-12)*S-4 (0-6)S-4 (0-6)*S-5 (0-6)S-6 (0-6)S-7 (0-6)S-7 (6-12)S-8 (0-6)S-9 (0-6)SS-1 (6-12)
DATE COLLECTED 07/16/2024 07/16/2024 07/16/2024 07/16/2024 07/16/2024 07/16/2024 07/16/2024 07/16/2024 07/16/2024 07/16/2024 07/16/2024 07/16/2024 07/16/2024 07/16/2024 07/16/2024
DEPTH (INCHES)0-6 6-12 0-6 0-6 6-12 6-12 0-6 0-6 0-6 0-6 0-6 6-12 0-6 0-6 6-12
ANALYTE EPA RSL1 UTAH ISL2 BACKGROUND3 Result Qualifier Result Qualifier Result Qualifier Result Qualifier Result Qualifier Result Qualifier Result Qualifier Result Qualifier Result Qualifier Result Qualifier Result Qualifier Result Qualifier Result Qualifier Result Qualifier Result Qualifier
ARSENIC 0.68 -7.2 10.4 12.8 7.52 15.6 10.7 25.9 23.6 34.6 6.5 4.48 23.3 13.8 6.5 14.8 12.4
BARIUM 15000 -580 203 217 111 107 118 213 260 268 75 52.5 374 145 70.7 76.3 262
CADMIUM 7.1 --1.94 2.2 0.891 2.49 1.28 2.37 8.79 7.95 0.609 0.681 3.1 1.16 0.909 1.35 2.5
CHROMIUM4 85000 -54 18.8 15.5 11.4 14.4 10.6 16.7 54.2 68.4 9.93 15.1 20.6 11.8 16.7 11.5 17
LEAD 200 -19 190 221 58.9 130 125 316 605 565 73.8 385 714 270 146 178 414
SELENIUM 390 -0.39 1.75 J 1.28 J 2.47 1.91 J 0.831 U 0.824 U 6.34 13.2 0.774 U 0.778 U 2.04 J 0.814 U 0.778 U 1.09 J 1.57 J
SILVER 390 --0.136 U 0.140 U 0.134 U 0.129 U 0.138 U 0.137 U 0.131 U 0.653 U 0.129 U 0.129 U 0.242 B J 0.229 B J 0.129 U 0.130 U 0.286 J
MERCURY 11 -0.09 0.238 0.318 0.074 0.0548 0.175 0.174 0.173 0.214 0.0474 0.0733 0.638 0.674 0.0529 0.0848 0.552
TPH-DRO (HIGH FRACTION)-500 -58.3 J 62 123 52.5 39 48.5 207 J 233 J 542 98.9 J 1180 118 60.4 60 143
TPH-GRO (LOW FRACTION)-500 -6.95 B 2.93 B J 9.85 2.32 B J 2.91 B J 3.36 B 2.37 J 1.81 J 0.629 J 1.1 J 7.03 3.67 B 1.4 B J 1.51 J 3.14 B J
OIL & GREASE -1000 -852 785 512 251 J3 J6 P1 162 150 8270 11500 1440 2070 5380 646 362 445 1220
BENZENE 1.2 --0.00713 0.0242 0.0162 0.00169 0.00329 0.00235 0.0163 0.00413 0.00101 J 0.000745 J 0.0398 0.0115 0.00713 0.00169 0.000911 J
N-BUTYLBENZENE 3900 --0.00726 U 0.00739 U 0.00612 U 0.00594 U 0.00645 U 0.00665 U 0.00631 U 0.00668 U 0.00539 U 0.00545 U 0.0083 J 0.00711 U 0.00544 U 0.00565 U 0.00705 U
SEC-BUTYLBENZENE 7800 --0.00398 U 0.00406 U 0.00335 U 0.00326 U 0.00353 U 0.00365 U 0.00345 U 0.00366 U 0.00296 U 0.00299 U 0.0048 J 0.00390 U 0.00298 U 0.0042 J 0.00387 U
CARBON TETRACHLORIDE 0.65 --0.00125 U 0.00127 U 0.00105 U 0.00101 U 0.00110 U 0.00114 U 0.00168 J 0.00165 J 0.000923 U 0.000932 U 0.00137 U 0.00122 U 0.000930 U 0.000966 U 0.00121 U
CHLOROFORM 0.32 --0.00143 U 0.00145 U 0.00120 U 0.00116 U 0.00126 U 0.00130 U 0.00123 U 0.00132 U 0.00106 U 0.00107 U 0.00157 U 0.00278 J 0.00107 U 0.00111 U 0.00138 U
1,1-DICHLOROETHANE 3.6 --0.000680 U 0.00479 0.00685 0.000555 U 0.000604 U 0.000621 U 0.000590 U 0.000625 U 0.000505 U 0.000510 U 0.000747 U 0.000665 U 0.000509 U 0.000529 U 0.00297 J
CIS-1,2-DICHLOROETHENE 63 --0.00198 J 0.0294 0.0285 0.000829 U 0.000902 U 0.000928 U 0.000881 U 0.000934 U 0.000754 U 0.000822 J 0.00144 J 0.0127 0.000760 U 0.000790 U 0.0106
TRANS-1,2-DICHLOROETHENE 70 --0.00144 U 0.00246 J 0.00338 J 0.00117 U 0.00128 U 0.00131 U 0.00125 U 0.00133 U 0.00107 U 0.00108 U 0.00158 U 0.00141 U 0.00108 U 0.00112 U 0.00185 J
ETHYLBENZENE 5.8 --0.00537 0.0104 0.0186 0.000833 U 0.00786 0.00332 0.0112 0.00649 0.00176 J 0.00208 J 0.0267 0.00867 0.00521 0.00312 0.00277 J
ISOPROPYLBENZENE 1900 --0.00221 J 0.00342 J 0.00775 0.000481 U 0.00427 0.00186 J 0.000511 U 0.00299 J 0.00058 J 0.000874 J 0.0117 0.00407 0.00195 J 0.00199 J 0.00215 J
P-ISOPROPYLTOLUENE ---0.0131 0.0114 0.00871 0.00289 U 0.0367 0.0111 0.0131 0.0123 0.00262 U 0.0046 J 0.07 0.0189 0.01 0.0132 0.00765
METHYLENE CHLORIDE 57 --0.00919 U 0.00934 U 0.00774 U 0.00797 J 0.00816 U 0.00840 U 0.00797 U 0.0119 J 0.00693 J 0.0085 J 0.0101 U 0.00900 U 0.00688 U 0.00828 J 0.00891 U
4-METHYL-2-PENTANONE (MIBK)33000 --0.00316 U 0.00320 U 0.00266 U 0.00258 U 0.0224 J 0.0114 J 0.00274 U 0.00290 U 0.00234 U 0.00237 U 0.00347 U 0.0175 J 0.0172 J 0.00734 J 0.00306 U
NAPHTHALENE 2 --0.0453 B 0.0477 B 0.0382 0.0113 J 0.0302 0.0183 0.0531 0.0459 0.00957 J 0.017 0.104 0.0499 0.0248 0.0118 J 0.0315 B
N-PROPYLBENZENE 3800 --0.00294 J 0.00355 J 0.00636 0.00108 U 0.00504 J 0.00199 J 0.00393 J 0.0028 J 0.000976 U 0.00108 J 0.0113 0.00492 J 0.00215 J 0.00328 J 0.00189 J
STYRENE 6000 --0.000317 U 0.000323 U 0.000267 U 0.000259 U 0.000281 U 0.000290 U 0.0574 0.0369 0.000235 U 0.000238 U 0.000349 U 0.000310 U 0.000237 U 0.000246 U 0.000307 U
TETRACHLOROETHENE 24 --0.0157 0.0492 0.0246 0.00101 U 0.00110 U 0.00113 U 0.0148 0.0122 0.00144 J 0.00501 0.0195 0.0164 0.000928 U 0.000964 U 0.209
TOLUENE 4900 --0.0403 0.0893 0.0921 0.00316 J 0.039 0.0153 0.0718 0.024 0.00693 0.00568 0.168 0.0534 0.0352 0.0168 0.00976
1,1,1-TRICHLOROETHANE 8100 --0.00128 U 0.00130 U 0.00108 U 0.00105 U 0.00113 U 0.00117 U 0.00111 U 0.00118 U 0.000948 U 0.000958 U 0.00140 U 0.00125 U 0.000956 U 0.000993 U 0.0148
TRICHLOROETHENE 0.94 --0.015 0.101 0.0477 0.000659 U 0.000717 U 0.000738 U 0.00957 0.0085 0.00201 0.0166 0.0205 0.0485 0.000605 U 0.000629 U 0.176
1,2,4-TRIMETHYLBENZENE 300 --0.0348 0.0408 0.0784 0.00426 J 0.0536 0.0213 0.0496 0.0312 0.00689 0.0144 0.172 0.0642 0.031 0.175 0.0273
1,2,3-TRIMETHYLBENZENE 340 --0.0252 0.0287 0.0438 0.00319 J 0.0344 0.0173 0.0313 0.0214 0.00503 J 0.0106 0.12 0.0365 0.0223 0.159 0.0165
1,3,5-TRIMETHYLBENZENE 270 --0.0107 0.011 0.043 0.00226 U 0.0233 0.0104 0.0173 0.012 0.00325 J 0.00455 J 0.0502 0.0243 0.00951 0.0402 0.0104
XYLENES, TOTAL 580 --0.0721 0.13 0.22 0.00886 0.0836 0.046 0.12 0.0641 0.0174 0.0244 0.374 0.147 0.0805 0.053 0.0456
Notes:
All results units are reported as mg/kg
U = Analyte not detected above laboratory method detection limit.
Gray highlighted concentrations indicate analyte was detected above laboratory method detection limit
Orange highlighted concentrations exceed either residentail soil RSLs or Utah ISLs
1EPA Regional Screening Level (RSL) for Residential Soil, May 2024. RSLs based on cancer risk of 10-6 and hazard quotient of one.
2Utah Initial Screening Level (ISL) for Leaking Underground Storage Tank Sites
3Background concentrations based on average concentrations presented in the Elemental Concentrations in Soils and Other Surficial Materials of the Conterminous United States, U.S. Geological Survey Professional Paper 1270, Shacklette, Boerngen, 1984
4RSL for chromium based on trivalent chromium
U = Analyte not detected. Value shown is the method detection limit.
TPH-DRO = Total Petroluem Hydrocarbons - Diesel Range Organics
TPH-GRO = Total Petroluem Hydrocarbons - Gasoline Range Organics
*Duplicate Sample
Laboratory Qualifiers (Qualifiers Subject to Change Pending Validation):
B: The same analyte is found in the associated blank
J: The identification of the analyte is acceptable; the reported value is an estimate
J6: The sample matrix interfered with the ability to make any accurate determination; spike value is low
P1: RPD value not applicable for sample concentrations less than 5 times the reporting limit.
J3: The associated batch QC was outside the established quality control range for precision
RCRA Metals
Petroleum Hydrocarbons
Volatile Orgainic Compounds
Table 2
Summary of Proposed Additional Sample Locations
Paxton Development
Salt Lake City, Utah
Sample Location
Location Previously
Sampled
(Yes/No)
Proposed Sample
Depth
(Inches bgs) Rational Parameters To Be Analyzed
S-1 Yes 12-18 Provide additional vertical characterization at existing sample location. Arsenic, Lead
S-3 Yes 12-18 Provide additional vertical characterization at existing sample location. Arsenic, Lead
S-4 Yes 12-18 Provide additional vertical characterization at existing sample location. Arsenic, Lead, Cadmium, Oil and Grease
S-6 Yes 12-18 Provide additional vertical characterization at existing sample location. Oil and Grease
S-7 Yes 12-18 Provide additional vertical characterization at existing sample location. Arsenic, Lead
SS-1 Yes 12-18 Provide additional vertical characterization at existing sample location. Arsenic, Lead, Oil and Grease
S-10 No 0-6, 6-12
Provide additional characterization in northern portion of the Site not currently
sampled. Location will include additional sample for vertical characterization. RCRA metals, TPH-GRO/DRO, Oil and Grease, VOCs
S-11 No 0-6
Provide additional characterization northern portion of the Site not currently
sampled. RCRA metals, TPH-GRO/DRO, Oil and Grease, VOCs
S-12 No 0-6, 6-12
Provide additional characterization in northern portion of the Site not currently
sampled. Location will include additional sample for vertical characterization. RCRA metals, TPH-GRO/DRO, Oil and Grease, VOCs
S-13 No 0-6
Provide additional characterization northern portion of the Site not currently
sampled. RCRA metals, TPH-GRO/DRO, Oil and Grease, VOCs
S-14 No 0-6, 6-12
portion of the Site. Location will include additional sample for vertical
characterization. RCRA metals, TPH-GRO/DRO, Oil and Grease, VOCs
S-15 No 0-6
Provide additional characterization in former shop area in the southestern
portion of the Site. Location will include additional sample for vertical RCRA metals, TPH-GRO/DRO, Oil and Grease, VOCs
Notes:
TPH-DRO = Total Petroleum Hydrocarbons - Diesel Range Organics
VOCs = Volatile Organic Compounds
RCRA = Resource Conservation and Recovery Act
bgs = Below ground surface
At existing locations where vertical characterization is proposed, only the parameters that were previously observed to exceed at that location will be analyzed. All other locations will be sampled for RCRA metals, TPH-
DRO/GRO, Oil and Grease and VOCs.