DERR-2025-002623

215 South State Street, Suite 500
Salt Lake City, UT 84111
PH 801.853.8308
www.geosyntec.com
RTC Paxton Project 6-17-2024
March 25, 2025
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 Remedial Action Plan Comments
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) comments on the Remedial Action Plan (RAP) for the Paxton
Site (Site) that were provided on March 19, 2025. DERR comments (shown in italics)
followed by our corresponding responses are provided below. A revised version of the
RAP has also been provided.
1. The DERR is concerned about the proposal that all excavations will be terminated at
the depth of groundwater. This is especially concerning around the hydraulic lifts
under the buildings where there is little data and a high level of uncertainty.
Additionally, previous sampling indicates oil and grease contamination was detected
at GP-5 from 7-8 feet, potentially within the smear zone. As petroleum impacts to
groundwater are present in the same vicinity, this soil represents a potential source
of contamination. To ensure sufficient removal of contaminated soil and any potential
sources, please include a contingency plan to address impacts at depth, especially
within the smear zone and below the water table, as needed.
Response: The text in Sections 2.2 and 2.4 has been modified to indicate that
the environmental professional will consult with UDEQ regarding the potential
need for excavation below the water table.
2. The RAP does not propose a strategy to address the petroleum impacts in
groundwater such as the TPH-GRO in MW-7, even though this concentration is above
the proposed cleanup goal. Due to the history of the Site, petroleum impacts reported
in groundwater are likely associated with the Site. Please propose a strategy to
address the groundwater contamination noted in this comment (see the DERR’s
previous Site Characterization Report comments, dated January 30, 2025).
Ms. Allison Stanley
March 25, 2025
Page 2

Response: The likely sources of the petroleum hydrocarbon impacts observed
at the Site will be removed/addressed in conjunction with the proposed building
foundation and pavement removal, hydraulic lift removal, shallow soil
excavation and subsurface soil excavations activities and the related
confirmation sampling. As a proactive measure, Paxton has proposed to apply
Oxygen Release Compound (ORC) to MW-7 and the surrounding area to
enhance the bioremediation of the petroleum hydrocarbons in groundwater at the
Site as detained in Section 2.5 of the RAP.
3. Trichloroethene (TCE) was reported above the proposed cleanup level at GP-4, but
no activities are proposed in the RAP to address this area. This is inconsistent with
previous representations made by the Applicant that this area would be addressed
during the cleanup (refer to the Site Characterization Workplan, dated June 19,
2024). To address this comment, please propose a strategy to address the TCE in soil
and revise the remedial action objectives accordingly.
Response: Subsurface excavation of TCE impacted soil has been added to the
RAP as detailed in Section 2.4 and the remedial action objectives have been
revised.
4. Please revise the text to note that continued monitoring will be proposed to ensure
the effectiveness of the VIMS system and a contingency plan will also be included in
the event the system needs to be adjusted. This is especially important since
contamination appears to be migrating on site and the Applicant has no control over
the off-site source. Alternatively, the Applicant can also propose an additional
strategy to address the concentrations migrating onto the site in hopes this will reduce
the costs and scope of future operations and maintenance requirements.
Response: Section 2.7 has been modified to clarify that on-going monitoring
and contingency measures will be described in the future Site Management Plan.
5. Please provide a schedule detailing the proposed remedial activities.
Response: A rough schedule of the proposed remedial activities has been added
as Section 4 of the RAP.
6. Please provide a contingency plan in the event unexpected contamination is
encountered during the cleanup.

Response: The RAP indicates that impacts identified during foundation and
pavement removal will be excavated and managed at a permitted off-site facility
(Section 2.1). It also states that if the extent of previously identified impacts
Ms. Allison Stanley
March 25, 2025
Page 3

extends beyond the planned extent of excavation, the excavations will be
expanded to remove these additional impacts, following which confirmation
samples will be collected (Section 2.2 and 2.3). An additional section (Section
2.5 Potential Unexpected Impacts) has been added to clarify measures to be
implemented if other unexpected impacts are encountered.

7. With regards to the conceptual model for the site, please note that institutional and
engineering controls are tools used at sites in concert with a primary remedy to
achieve cleanup goals and ensure protection of public health.
Response: We concur and note that this appears to be well aligned with the
measures proposed in the RAP.
8. Section 1.6.1, third sentence - The DERR disagrees with the statement that
exceedances of TCE and Oil and Grease in the subsurface soil are likely influenced
by impacted groundwater. Based on the data, these constituents were not reported in
groundwater above screening levels. To address this comment, please remove this
statement, and all other similar references, from the text.
Response: References to potential influence by groundwater to these observed
exceedances have been removed from the text.
9. Section 1.8, first sentence - There are no cleanup goals proposed for the volatile
organic compounds (VOCs) in groundwater. However, VOCs have been reported
above the Maximum Contaminant Level in many of the monitoring wells. While
engineering and institutional controls can be effective tools in concert with a primary
remedy, established cleanup goals are necessary to monitor the efficacy of these
measures. Please revise the text to address this comment.
Response: Cleanup goals for groundwater have been added to Section 1.8.
10. Section 2.1, third sentence - Please state that disposal documentation for the
hydraulic fluid will be submitted in the Remedial Action Completion Report.
Additionally, all disposal activities should be conducted at a ‘permitted’ off-site
disposal facility able to accept the specific waste stream. Please revise the text
accordingly.
Response: The text previously presented in Section 2.1 (Building Foundation
and Hydraulic Lift Removal) of the Draft RAP has been revised and split into
two sections, including: Section 2.1 (Building Foundation and Pavement
Removal) and Section 2.2 (Hydraulic Lift Removal) to provide clarification
regarding the activities that will be conducted.
Ms. Allison Stanley
March 25, 2025
Page 4

Section 3.8 indicates that all materials generated during RAP implementation
will be managed at permitted off-site facilities and waste manifest and
documentation will be provided with the Remedial Action Completion Report.
11. Section 2.1, seventh sentence - Please state that confirmation samples will be
collected to determine the extent of excavation if impacted soil is identified beneath
the foundations. Additionally, laboratory samples should be collected under the
foundations and not rely strictly on field instruments. Since metals are constituents of
concern at the site, please include metals during sampling under the foundations and
any excavations where metals may be present.
Response: During the site characterization activities, sampling was conducted
beneath the Site buildings and paved areas. Impacted soil was identified beneath
the Quonset hut structure (Sample S-15) and pavement in the north central
portion of the Site (Samples S-11 and S-12). These areas have been included in
the proposed soil excavation area and confirmation sampling will be conducted
following the excavation as detailed in the RAP. If additional impacts are
identified in these areas or other paved areas, additional soil will be removed
and/or opportunistic or confirmation samples will be collected. RCRA metals
have been included as an analyte for these samples.
12. Section 2.1, seventh sentence - Please revise the text to note that the environmental
professional will collect opportunity samples if signs of previously unencountered
contamination are observed during removal activities at the site.
Response: Please see response to Comment #11.
13. Section 2.1, ninth sentence - Please change the text to indicate that sidewall samples
will be collected, whether or not impacts are identified with the anticipated field
screening efforts, to confirm that the excavation addresses the horizontal extent of the
contamination.
Response: This point has been clarified in the revised text.
14. Section 2.2, second sentence - Deeper samples (6-12 inches and 12-18 inches) were
not collected from locations S-5, S-11, and S-15. Please ensure that confirmation
samples are proposed near each of these locations to verify that the vertical extent of
contamination has been removed.
Response: Text has been added to the second paragraph of this section (now
Section 2.3) indicating that confirmation samples will be co-located with prior
sample locations where the vertical extent of impacts were not previously
delineated.
Ms. Allison Stanley
March 25, 2025
Page 5

15. Section 2.2, fifth sentence - Similar to comment #12, confirmation samples are not
proposed for the sidewalls of the shallow soil excavation. Please indicate that
sidewall samples will be collected if a sidewall exists. If collection of sidewall samples
is not possible, please propose a strategy to confirm that the excavation addresses the
horizontal extent of the contamination.
Response: Side wall samples will be collected and have been described in
Section 2.1 to 2.3 of the RAP.
16. Section 2.7 - Please include the analytical method for 1,4-dioxane.
Response: The analytical method for 1,4-dioxane is US EPA Method 8260B, the
same method that will be used for other VOCs.
17. Section 3.5 - In the text, please discuss track out procedures and management
practices for stockpiled material (e.g., covered, lined with a berm for stormwater
management). Appropriate construction management practices should reduce the
migration of contamination.
Response: Additional descriptions of best management practices to be
implemented to reduce the potential for spreading of impacts via stormwater
have included in Section 3.5. Track out and dust control measures are described
in Sections 3.3 and 3.4, respectively.
18. Figure 4 - The sample collected at GP-4 between 6-7 feet is missing from the figure.
Please address.
Response: The sample interval has been added to Figure 4.
19. Appendix C, second sentence - The Salt Lake County parcel 15-12-457-015-0000 is
not part of the VCP project boundaries. Please remove this parcel from the public
notice.
Response: The parcel has been removed from the public notice text.
20. Appendix C, fifth paragraph - The last name “Stanley” is misspelled. Please correct
this in the text.
Response: The typo has been corrected in the public notice text.

Ms. Allison Stanley
March 25, 2025
Page 6

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)