DERR-2025-000681

215 South State Street, Suite 500
Salt Lake City, UT 84111
PH 801.853.8308
www.geosyntec.com
RTC Paxton Project 6-17-2024
June 19, 2024
Ms. Allison Stanley
Project Manager
Division of Environmental Response and Remediation
Utah Department of Environmental Quality
195 North 1950 West
Salt Lake City, Utah 84116

Subject: Response to Comments
Site Characterization Work Plan and Quality Assurance Project Plan
Paxton Site - Voluntary Cleanup Program Site #129

Dear Ms. Stanley,
Geosyntec Consultants (Geosyntec) has prepared this letter to provide written responses
to the comments provided by the Utah Division of Environmental Response and
Remediation’s (DERR’s) June 14, 2024 comments on the Site Characterization Work
Plan (SCW) and Quality Assurance Project Plan (QAPP) for the Paxton Site (Site).
Provided below are the DERR comments in italics, followed by our corresponding
response. Revised versions of the SCW and QAPP have also been provided.
General Comments on the SCW
1. Since characterization activities are not proposed under the buildings and other
hardscape locations in the Site Characterization Workplan (SCW), further sampling
should be proposed in the Remedial Action Plan (RAP) once the buildings have been
demolished and the foundations/hardscape removed. Due to the age of the Site,
potential unknowns may exist under the buildings beyond the reported hydraulic lifts.
An environmental professional should be on-site as these surfaces are removed.
Response: Sampling beneath the buildings and paved areas will be evaluated
following completion of the SCW activities and will be proposed in the RAP.
An environmental professional will be on-site during the removal of paved areas
and building foundations to help evaluate the need for sampling. These points
have been clarified in Section 1.5 of the updated SCW.
2. It is acceptable to screen against the Initial Screening Levels (for TPH-DRO/GRO
and TRPH only). However, the Initial Screening Levels are conservative. To better
evaluate the potential risk and address any uncertainty, the Applicant is encouraged
to Fractionate the highest concentrations using the UST Fractionation method.
Ms. Allison Stanley
June 19, 2024
Page 2

Response to DERR Comments 6-19-2024
Response: Petroleum fractionation may be conducted as described in Section
2.4 of the updated SCW.
3. Trichloroethylene (TCE) was reported to exceed the soil screening level in GP-4 from
6-7 feet below ground surface (bgs). However, the source of this contaminant is
unknown. To address this uncertainty, please propose further sampling to define the
nature and extent of contamination. This information will be necessary to help
develop a remedy.
Response: GP-4 is the only location where soil screening level exceedances
were previously identified for TCE and no groundwater screening criteria
exceedances were identified, suggesting that the extent of impacts is limited. It
is envisioned that impacted soil from this area will be excavated and disposed of
off-site. Confirmation sampling will be conducted in conjunction with these
activities. These excavation and confirmation sampling activities will be
described in the RAP.
4. It appears the proposed sampling will be conducted prior to the removal of the debris
from the Site. Until the Site is cleared and inspected, it should be assumed there are
possible unknowns across the property that will warrant additional characterization.
To address this comment, please include opportunity samples in the SCW and clearly
state that the Site will be inspected and additional sampling conducted, as needed,
prior to designing a remedial action.
Response: A description of potential opportunistic samples has been included
in Section 2.1 of the updated SCW.
5. To better understand the potential risk at the Site and design a future vapor mitigation
strategy, soil gas samples or sub-slab samples should be collected. It is acceptable to
conduct this sampling after the next round of groundwater data is collected so data
can be reviewed and samples can be biased toward the future building footprint and
areas of highest contamination.
Response: Soil gas sampling has been added to the scope of work as described
in Sections 1.5 and 2.3 of the updated SCW.
Specific Comments on the SCW
1. Table of Contents - Figure 1 depicting the Site location is referenced in the SCW but
is not attached to the document. Please attach the figure.
Response: Figure 1 has been added to the updated SCW.
Ms. Allison Stanley
June 19, 2024
Page 3

Response to DERR Comments 6-19-2024
2. Section 1.2, sentence 5 - The Site was not accepted into the VCP on April 3, 2024, but
rather on April 1, 2024, when the DERR signed the VCP eligibility letter. Please
correct this date in the text.
Response: The correct date has been included in the updated SCW.
3. Section 1.3, sentence 25 - Metals were not analyzed in the groundwater at monitoring
well MW-3 but at sampling point GP-1. Please correct this statement in the text.
Response: The correct sampling point is referenced in the updated SCW.
4. Section 1.5, sentence 6 - It is premature to indicate that an updated round of
groundwater sampling will allow the Site to move directly into the RAP. Please clarify
the last sentence by adding the statement, “to evaluate the need for potential further
characterization and/or remedial action”.
Response: The requested statement has been added to Section 1.5 of the updated
the SCW.
5. Section 1.5, sentence 7 - The SCW discusses detailed delineation near the “unknown
vault”; however, this was identified to be an in-ground lift in Section 1.3. Please use
consistent language throughout the document when referring to this structure.
Response: The structure has been referenced as the “in-ground lift” throughout
the updated SCW.
6. Section 1.5, sentence 7 - The SCW notes that confirmation samples will be collected
following the removal of impacted soils as part of the RAP. Please be aware that the
purpose of the SCW is not to outline a remedy for the Site. This will be done in the
final RAP. The DERR will need to review the characterization data before evaluating
a final remedy for the site.
Response: The confirmation sampling will be described in detail in the RAP and
the RAP will be implemented following DERR review and approval. Reference
to the confirmation sampling was included in the SCW to emphasize that the
impacted soil would be removed and that the need for additional delineation does
not appear to be warranted during implementation of the SCW.
7. Section 2.1, sentence 5 - The SCW does not identify where the four deeper soil samples
(6-12” bgs) will be located. Please indicate in the text if these sample locations are
already determined and where, or if they will be identified in the field. Additionally,
please indicate if these samples will be collected from previous locations, such as SS-
1.
Ms. Allison Stanley
June 19, 2024
Page 4

Response to DERR Comments 6-19-2024
Response: Section 2.1 of the SCW has been updated to indicate that one of the
subsurface soil samples will be collected from the former SS-1 sample location
and the remaining three sample locations will be selected during the sampling
activities based on visual observations.
8. Section 2.8, sentence 1 - Since screening levels may change throughout the project,
please indicate that data will be compared to the “most current” Screening Levels to
ensure that project objectives remain protective of human health and the
environment.
Response: The requested language has been added to the updated SCW.
9. References - The date of the project QAPP is May 2024. Please correct this date in
the listed reference.
Response: The correct date has been included in the updated SCW.
10. Appendix A, Table 1A - There are still some transcription errors in the historical data
table. The transcription errors are found for GP-1 through GP-4, as the results for
1,1-dichloroethene and cis-1,2-dichloroethene are switched. Please see the limited
subsurface investigation from September 2023 for the correct lab results.
Response: The transcription errors have been addressed in the updated SCW.
General Comment on the QAPP
1. One of the last elements of EPA’s Quality Assurance guidance is the reconciliation
with user requirements. Please include this section and discuss how data and
information will be reconciled with the project objectives to assess the overall success
of sampling activities.
Response: Language describing reconciliation of data from the site
characterization has been added as Section 4.4 of the updated QAPP.
Specific Comments on the QAPP
1. Section 1.1, sentence 8 - Similar to the SCW, the Site did not enter the VCP on April
3, 2024, but rather on April 1, 2024, when the DERR signed the eligibility letter.
Please correct this in the text.
Response: The correct date has been included in the updated QAPP.
Ms. Allison Stanley
June 19, 2024
Page 5

Response to DERR Comments 6-19-2024
2. Section 2.9.5, sentence 10 - Please revise the text to note that groundwater
concentrations will be screened against EPA RSL Tapwater values if there is no MCL.
This includes compounds such as 1, 4 Dioxane.
Response: The text has been revised as requested in the updated QAPP.
3. Section 3.2, Table 1 - To ensure that procedures are properly met when collecting
samples, please provide a Standard Operating Procedure (SOP) for general sample
labeling, handling, custody, and documentation or specify where in the QAPP this
information is clearly articulated.
Response: Procedures for sample handling, custody, and documentation are
included in Section 3.4 of the updated QAPP.
4. Section 3.6, sentence 15 - Please revise the QAPP to indicate the frequency of the
rinsate blank collection will be specified in the SCW.
Response: Rinsate blanks will be collected at a frequency of 5 percent as
referenced in Section 3.6 of the updated QAPP.
5. Section 4.4, sentence 1 - Please revise the text to specify the individual responsible
for conducting the data verification and validation, and how data reviews will be
presented in final documents submitted under the VCP. Data review summaries
should be included as part of the final reports detailing the investigations and cleanup
and usability of the data. If laboratory and field corrective actions are required, the
consultant should coordinate with the DERR.
Response: Additional details regarding data validation have been added to
Section 4.3 of the updated QAPP.

Ms. Allison Stanley
June 19, 2024
Page 6

Response to DERR Comments 6-19-2024
Closing
We appreciate your review of the provided responses to the DERR’s comments. If you
have any questions or would like additional information, please contact us at 801-853-
8185.
Sincerely,
Brian Smith, P.G.
Senior Geologist
Brent C. Robinson, P.E.
Senior Principal
cc:
Bruce Bastian (Paxton Project LLC)