DERR-2025-005188

Facilities | Environmental | Geotechnical | Materials 1
Cover Page
Post Remedial Action Risk Evaluation
21st & 21st Properties
NEC 2100 South and 2100 East (2145 East 2100 South)
Salt Lake City, Salt Lake County, Utah
July 9, 2025 | Terracon Project No. 61197460
Prepared for:
Rockworth Companies
Holladay, Utah
6952 South High Tech Drive Ste. B
Midvale, Utah 84047
P [phone]
Terracon.com
Facilities | Environmental | Geotechnical | Materials i
Cover Letter
July 9, 2025
Rockworth Companies
4655 South 2300 East, Suite 205
Holladay, Utah 84117
Attn: Mr. Tom Henriod
P: [phone]
E: [e-mail]
Re:Post Remedial Action Risk Evaluation
21st & 21st Properties
NEC 2145 East 2100 South
Salt Lake City, Salt Lake County, Utah
Terracon Project No. 61197460
Dear Mr. Henriod:
Terracon Consultants, Inc. (Terracon) has prepared this Risk Evaluation for the above-
referenced site to satisfy the requirements of the Utah Department of Environmental Quality
(DEQ) Division of Waste Management and Radiation Control’s (DWMRC) Environmental
Cleanup Program.
Terracon has performed this work pursuant to agency requests and to the Remedial Action
Plan (RAP; Terracon; dated April 7, 2021) and subsequent Amendments submitted to the DEQ
DWMRC, who is the regulatory agency overseeing the cleanup of chlorinated solvents
present in the groundwater under the site.
We appreciate the opportunity to have performed these services for you. Please contact our
office at [phone] if you have questions regarding this information or if we can
provide any other services.
Sincerely,
Terracon Consultants, Inc.
Andrew Turner Amy Austin
Project Manager Authorized Project Reviewer
' P \ ' X V W L Q
Facilities | Environmental | Geotechnical | Materials ii
Table Of Contents
1.0 Introduction ................................................................................ 1
1.1 Site Description ..................................................................................... 1
1.2 Project Background ................................................................................ 1
1.3 Standard of Care .................................................................................... 3
1.4 Reliance ................................................................................................ 3
2.0 Conceptual Site Model .................................................................. 3
2.1 Sources, Release Mechanisms, and Affected Media ..................................... 4
2.2 Receptors and Routes of Exposure ............................................................ 4
2.3 Contaminants of Potential Concern ........................................................... 4
3.0 Risk Calculations .......................................................................... 6
3.1 RSL Calculator Data Inputs ...................................................................... 6
3.2 Results of the Onsite Risk Evaluation ........................................................ 8
3.3 Soil-To-Groundwater Pathway Evaluation .................................................. 9
4.0 Ecological Risk Assessment............................................................ 9
5.0 Conclusions ............................................................................... 10
6.0 References ................................................................................ 11
Facilities | Environmental | Geotechnical | Materials iii
APPENDICES
Appendix A Exhibits
Exhibit 1:Topographic Site Overview
Exhibit 2:Aerial Overview of Site
Exhibit 3:Conceptual Site Model
Appendix B Data Tables
Table 1: Maximum Concentrations of COPCs—Soil
Table 2: Maximum Concentrations of COPCs—Groundwater
Appendix C RSL Calculator Outputs
Appendix D Application For A Waiver Of An Ecological Risk Assessment
Risk Evaluation
21st and 21st, Salt Lake City, Utah
July 9, 2025 | Terracon Project No. 61197460
Facilities | Environmental | Geotechnical | Materials 1
1.0 Introduction
1.1 Site Description
Site Name 21st & 21st Properties
Site Location/Address 2145 East 2100 South, Salt Lake City, Utah
Land Area
Consolidated Parcel Number: 16-15-359-018
Total land area: 2.46 acres
Redevelopment Site Use
Multi-use commercial and residential development.
North Building: below grade, open air parking
structure with residential apartments above parking
structure.
South Building: slab on grade commercial retail at
ground level with residential above the first floor.
Exhibit 1 (Appendix A) presents the general location and topography of the Site, which was
reproduced from a portion of the United States Geological Survey (USGS) 7.5-minute series
topographical map. The property structures have been razed, and construction of a multi-
use commercial/residential structure on-site is now nearly complete. Exhibit 2 shows the
current property with the new development and location of the post construction monitoring
wells installed at the Site.
1.2 Project Background
The Site was formerly composed of multiple parcels of commercial development consisting
of multi-tenant commercial and retail buildings including restaurants, offices, a gas station,
and dry-cleaning operations. Phase I Environmental Site Assessments (Phase I ESAs) and
subsequent subsurface investigations conducted at the Site over multiple years identified a
release of chlorinated solvents likely originating from dry cleaning facilities operating at the
Site and a release of petroleum hydrocarbons originating from a historical gas station that
operated in the southwest portion of the Site.
Rockworth Companies purchased the properties with the intent to redevelop the land for
mixed residential and commercial development. The Site has been combined into one parcel
consisting of 2.46 acres now addressed as 2145 East 2100 South and referred to as the 21st
& 21st Properties (the Site). At the request of Rockworth Companies, the Site was enrolled
in the Utah Department of Environmental Quality (DEQ) Division of Waste Management and
Risk Evaluation
21st and 21st, Salt Lake City, Utah
July 9, 2025 | Terracon Project No. 61197460
Facilities | Environmental | Geotechnical | Materials 2
Radiation Control (DWMRC) Environmental Cleanup Program to properly manage
environmental impacts during construction and implement protective measures post
construction.
Terracon Consultants, Inc. (Terracon), developed a Remedial Action Plan (RAP; Terracon;
dated April 7, 2021) and subsequent Amendments to address impacts documented at the
property. The DWMRC is the regulatory agency overseeing the cleanup of chlorinated
solvents. Releases from underground storage tanks are regulated by the UDEQ Division of
Environmental Response and Remediation (DERR) Leaking Underground Storage Tank
(LUST) Program.
Multiple corrective actions were implemented during construction, and all requirements
detailed in the RAP and Amendments were followed. A Corrective Measures Implementation
Report (CMIR) was submitted to DWMRC on October 11, 2024 (Terracon, 2024a). This
report discussed all of the remediation work conducted on the Site. The work included soil
sampling, excavation, and characterization in multiple areas of the site, soil characterization
in isolated suspect areas, LUST soil excavation in the southwest portion of the site, soil
transport and disposal, and confirmation sampling.
A series of five monitoring wells were installed to monitor groundwater both on and off-site.
Exhibit 2 (Appendix A) is a site diagram that shows the monitoring well locations. The three
on-site monitoring wells and two off-site monitoring wells were sampled quarterly in 2024.
Per the Revised Site Management Plan Outline (February 2022), these wells will now be
monitored semi-annually for the next two years. The last semi-annual sampling event was
conducted in June 2025. Each well exceeded the Residential and Commercial Vapor
Intrusion Screening Levels (VISLs) for tetrachloroethene (PCE) (Terracon, 2025).
In order to protect future residents and occupants of the buildings, a vapor intrusion
mitigation system (VIMS) was designed and installed beneath the elevator and stairwells of
the North Building open-air sub-grade parking structure and the entire footprint of the
South Building. The details of the VIMS design and installation are provided in a separate
comprehensive report (Terracon report dated July 1, 2024, Terracon, 2024b), which was
included as Appendix F in the CMIR.
DWMRC requested that soil gas sampling in the exhaust vent risers of the VIMS system be
conducted to ensure that the system is working as designed and potential soil gas impacts
are being properly mitigated and vented away from any residential or commercial areas.
Upon completion of this sampling and submittal of the soil gas results, DWMRC issued a
supplemental letter on April 10, 2025, requesting indoor air sampling at two locations at the
Site in order to evaluate the risk of soil gas exposure. These locations were near the R-2
riser within the southern building and within the underground parking garage under a
portion of the northern building.
Risk Evaluation
21st and 21st, Salt Lake City, Utah
July 9, 2025 | Terracon Project No. 61197460
Facilities | Environmental | Geotechnical | Materials 3
1.3 Standard of Care
Terracon’s services were performed in a manner consistent with generally-accepted
practices of the profession undertaken in similar studies in the same geographical area
during the same time period. Terracon makes no warranties, either express or implied,
regarding the findings, conclusions, or recommendations. Please note that Terracon does
not warrant the work of laboratories, regulatory agencies, or other third parties supplying
information used in the preparation of the report.
1.4 Reliance
This report has been prepared for the exclusive use and reliance of Rockworth Companies
and the DEQ. Use or reliance by any other party is prohibited without the written
authorization of the Rockworth Companies and Terracon.
Reliance on the report by the client and all authorized parties will be subject to the terms,
conditions, and limitations stated in the proposal, report, and Terracon’s Terms and
Conditions. The limitation of liability defined in the Terms and Conditions is the aggregate
limit of Terracon’s liability to the client and all relying parties.
2.0 Conceptual Site Model
The objective of the Risk Evaluation was to evaluate whether impacted soil, groundwater,
and/or soil vapor on-site is contaminated to the extent it poses a human health risk at
levels above target maximum risk levels and hazard indices. A Conceptual Site Model (CSM)
was developed to document the potential for exposure to contaminants at the site based on
the source(s) of contamination, the release mechanism(s), potential routes of exposure
(ROE), representative concentrations of contaminants of potential concern (COPCs), and
receptors (i.e., property occupants) in order to evaluate site-specific risks associated with
the COPCs remaining. A graphical representation of the CSM is presented as Exhibit 3
(Appendix A).
Concentrations of COPCs remaining in soils were compared to the EPAs Risk-based
Screening Level Generic Tables and Dilution Attenuation Factor x 20 (DAF 20) soil screening
level (Table 1, Appendix B). Concentrations of COPCs in groundwater were compared to
EPA’s Maximum Contamination Levels (MCLs) for drinking water and Target Groundwater
Concentration (TGC) VISLs (Table 2). Concentrations of COPCs in indoor air were compared
to the EPA Target Indoor Air Concentration VISLs.
Verification of operation of the VIMS was proposed to DWMRC in order to verify that the
system is properly operating. Additionally, indoor air sampling within a commercial
operation in the southern building (near riser R-2) and within the open-air underground
parking garage under a portion of the north building was conducted. This sampling of the
Risk Evaluation
21st and 21st, Salt Lake City, Utah
July 9, 2025 | Terracon Project No. 61197460
Facilities | Environmental | Geotechnical | Materials 4
vent risers and indoor air was recently conducted, and results were discussed in a separate
report.
2.1 Sources, Release Mechanisms, and Affected Media
Historic operations that have impacted the Site include dry-cleaning facilities and a gas
station. Facilities of this nature have used various chemicals including chlorinated solvents
and petroleum hydrocarbons. Investigations conducted at the site reported soil and
groundwater impacted with petroleum hydrocarbons and VOCs.
2.2 Receptors and Routes of Exposure
The current and future use of the site is residential with commercial use on the ground
level. The on-site buildings are new with no significant renovations to the buildings expected
in the near future. No subsurface excavation, construction, or demolition is currently
planned for the site. In order to be conservative, this Risk Evaluation uses residential land
use to represent the potential residential receptors. The following routes of exposure were
evaluated in this Risk Evaluation.
Soil Routes of Exposure: Ingestion of soil, inhalation of vapor emissions and particulates,
dermal contact with soil, and leaching to groundwater are the routes of exposure considered
for soils in the Risk Evaluation. These exposure routes are considered to be incomplete
pathways for the receptors since the site is completely covered with concrete and/or
asphalt, backfilled with clean soil as appropriate, and/or has a VIMS installed above the soil
and below the residential buildings.
Groundwater Routes of Exposure: Ingestion and dermal contact are the routes of
exposure considered for groundwater in the Risk Evaluation. These exposure routes are
considered to be incomplete pathways since receptors will not have access to site
groundwater, the site is capped with concrete and/or asphalt, and groundwater is at a
considerable depth below the surface (approximately 25 feet bgs). A pathway for
construction workers may be present in the event that future excavations go below the
groundwater table. However, to provide a conservative evaluation regarding exposure risks,
all routes were included in the Risk Evaluation.
Soil Vapor Routes of Exposure: Inhalation of vapor emissions is not expected to be a
route of exposure due to the construction of the VIMS. Indoor air sampling within a
commercial space in the South Building was conducted to verify this exposure potential. The
pathway is incomplete. Sampling from the VIMS exhaust was also recently conducted.
2.3 Contaminants of Potential Concern
COPCs were identified as those compounds detected above laboratory detection limits. Soil
COPCs used for risk calculations are listed in Table 1 (Appendix B). These concentrations are
Risk Evaluation
21st and 21st, Salt Lake City, Utah
July 9, 2025 | Terracon Project No. 61197460
Facilities | Environmental | Geotechnical | Materials 5
based on soil confirmation samples collected after soil excavation and prior to backfill and
site development or from generated soil stockpiles that were later reused during side
development. Groundwater COPCs used for risk calculations are listed in Table 2 (Appendix
B). These concentrations are based on the most recent groundwater sampling conducted at
the site (June 2025). The maximum detected concentrations were used for the calculations.
Indoor air COPCs were non-detect (ND) for the indoor air sampling in the South Building, so
no values were imputed for soil gas.
2.3.1 Soils
Nine VOCs were reported above laboratory detection limits in soil. These detections were
reported from soil confirmation samples collected at depth, the bottom of pre-
characterization samples, or samples from stockpiles where the soil was reused at the site.
The list of COPCs for soil are presented in Table 1 (Appendix B). Exceedances of the RSLs
and DAF-20 screening levels are discussed below for the various COPC types.
No concentrations of COPCs in soil exceeded the Residential or Industrial RSLs. PCE was
detected in stockpile PSP-8 at a concentration of 5,420 micrograms per kilogram (µg/kg),
exceeding the DAF 20 soil screening level (SSL) of 102 µg/kg. 1,1,2,2-Tetrachloroethane
and 1,1,2-trichloroethane were detected in footer sample WS-14 at a depth of
approximately 7 feet bgs and concentrations of 107 and 103 µg/kg, respectively, exceeding
the DAF 20 SSLs of 0.6 µg/kg and 32 µg/kg. 1,2-Dichloroethane was detected at pre-
characterization sample SB-4 at a depth of 3 feet bgs and a concentration of 72 µg/kg,
exceeding the DAF 20 SSL of 28 µg/kg. Methylene chloride was detected at pre-
characterization sample SB-10 at 2.5–3 feet bgs and a concentration of 14.2 µg/kg,
exceeding the soil SSL of 1.3 µg/kg. Chloroform was detected at Blue Plate sample BP-5 at
11.5 feet bgs at a concentration of 28 µg/kg, exceeding the soil SSL of 22 µg/kg.
2.3.2 Groundwater
PCE was detected at 2.3 milligrams per liter (mg/l) in MW-5, which exceeds the EPA MCL
and TGC VISL for Residential and Commercial sites. Chloroform was detected at 0.00122J
mg/l in MW-1A, which exceeds the Residential VISL of 0.000814 mg/l. Naphthalene was
detected in MW-1A at 0.0222J mg/l in MW-1A, exceeding the Commercial VISL of 0.0201
mg/l. Table 2 (Appendix B) lists the COPCs for groundwater.
2.3.3 Soil Vapor
The southern buildings were constructed with a VIMS in order to mitigate any potential
vapor intrusion. Additionally, there is no residential use located on the first floor. The
northern building has an open-air underground parking garage below the majority of the
building, and there is no residential use located on the first floor for the remaining section.
There is not a complete exposure pathway for soil vapor exposure.
Risk Evaluation
21st and 21st, Salt Lake City, Utah
July 9, 2025 | Terracon Project No. 61197460
Facilities | Environmental | Geotechnical | Materials 6
An indoor air sample was collected from the South Building adjacent to Riser R-2 where the
VIMS exhaust had the highest COPC concentrations. COPC concentrations were ND. An
additional indoor air sample was collected within the open-air parking garage under a
portion of the North Building. The concentration of PCE was 122 µg/m3, exceeding the
Commercial VISL of 47.2 µg/m3.
3.0 Risk Calculations
Terracon prepared this Risk Evaluation using the EPAs online RSL calculator (https://epa-
prgs.ornl.gov/cgi-bin/chemicals/csl_search), EPAs VISL calculator (https://epa-
visl.ornl.gov/cgi-bin/visl_search) to evaluate the cumulative risk posed by COPCs at the site
in soil and groundwater.
3.1 RSL Calculator Data Inputs
Parameter Input
Screening
Level Type
Regional Screening Levels (RSLs)
Hazard Index 1.0—was selected at the direction of Utah Department of Environmental
Quality (DEQ) to evaluate cumulative the non-cancer risk posed by
COPCs at the site.
Target Risk 10-6 (i.e., one in one million)—was selected at the direction of DEQ to
evaluate the cumulative cancer risk posed by COPCs at the site.
Scenario Resident—To be conservative, the Resident was initially selected as the
receptor (see Section 2.2). Other scenarios were also run for indoor
worker, outdoor worker, and construction worker.
Media The RSL calculator was run for soil, tap water, and air media.
Screening
Level Choice
Site Specific inputs were selected, as required by the next choice “Risk
Output.” Within this parameter the option “User-provided” was selected.
Risk Evaluation
21st and 21st, Salt Lake City, Utah
July 9, 2025 | Terracon Project No. 61197460
Facilities | Environmental | Geotechnical | Materials 7
Parameter Input
Risk Output Risk Output was affirmative as this directs the RSL Calculator to present
site-specific risk posed by each individual COPC and the cumulative risk.
RfD/RdC
Choice
Chronic
Chemicals Soils—the COPC identified for soil at the site were entered in this
section, as discussed in Section 2.3.1 and listed in Table 1 (Appendix B).
Tapwater—the COPC identified for groundwater at the site were
entered in this section, as discussed in Section 2.3.2 and listed in Table
2 (Appendix B).
Soil Gas (Air) – no COPCs for soil gas were entered due to having no
detections in the commercial indoor air sample collected.
Particulate
Emission
Factor Wind
Driven
The calculator allows for the selection of selected site-specific
parameters, based on guidance from the updated Supplemental
Guidance for Developing Soil Screening Levels for Superfund Sites (EPA,
2002). For the City—Salt Lake City was selected as the Climatic Zone.
Volatilization
Factor and
Soil Saturation
The calculator allows for the selection of selected site-specific
parameters, based on guidance from the updated Supplemental
Guidance for Developing Soil Screening Levels for Superfund Sites (EPA,
2002). For the City—Salt Lake City was selected as the Climatic Zone.
Volatilization
Factor—Mass
Limit
As noted above, based on EPA guidance, and site-specific parameters
selected in this section (EPA 2002).
Average source depth (dS): 1.0 meters (3 feet) was the average depth
of the soil samples collected from the site where the soil remains.
City: Salt Lake City was selected as the Climatic Zone.
Terracon input the highest concentrations of all soil COPCs remaining after excavation and
all groundwater COPCs reported in the most recent groundwater sampling event. All other
parameters were default parameters associated with the options described above, except
where indicated.
Risk Evaluation
21st and 21st, Salt Lake City, Utah
July 9, 2025 | Terracon Project No. 61197460
Facilities | Environmental | Geotechnical | Materials 8
3.2 Results of the Onsite Risk Evaluation
The following table summarizes the results from the EPA’s software for the Resident
Scenario.
Carcinogenic Risk Non-Carcinogenic Hazard Index
Soil = 1.92 x 10-7 Soil (Adult) = 0.0205 Soil (Child) = 0.0315
Tapwater = 3.99 x 10-4 Tapwater (Adult) = 49.6 Tapwater (Child) = 60.6
Sum of Soil and Tapwater
= 3.99 x 10-4
Sum of Soil and Tapwater
(Adult) = 49.6
Sum of Soil and Tapwater
(Child) = 60.6
There is no risk from soil gas due to the COPCs being ND in the sample collected from the
commercial space within the South Building.
The following table summarizes the results from the EPA’s software for the Indoor Worker
Scenario.
Carcinogenic Risk Non-Carcinogenic Hazard Index
Soil = 3.58 x 10-8 Soil = 0.00502
There is no risk from soil gas due to the COPCs being ND in the sample collected from the
commercial space within the South Building.
The following table summarizes the results from the EPAs software for the Outdoor Worker
Scenario.
Carcinogenic Risk Non-Carcinogenic Hazard Index
Soil = 3.85 x 10-8 Soil = 0.00488
There is no risk from soil gas due to the COPCs being ND in the sample collected from the
commercial space within the South Building. Although the sample collected from the
underground parking garage did have a detection of PCE, this space is vented to the
atmosphere and not designed for commercial business where long-term and prolonged
exposure would be expected to occur. Any potential exposure would be very brief and
sporadic (i.e. people walking from their car to the elevator), and this would not be
considered a working environment.
Risk Evaluation
21st and 21st, Salt Lake City, Utah
July 9, 2025 | Terracon Project No. 61197460
Facilities | Environmental | Geotechnical | Materials 9
The following table summarizes the results from the EPAs software for the Construction
Worker Scenario.
Carcinogenic Risk Non-Carcinogenic Hazard Index
Soil = 2.58 x 10-8 Soil (Adult) = 0.0331
There are no published tapwater or soil gas parameters under the Construction Worker
Scenario.
Appendix C contains the input and output information from the EPA software.
Based on the calculations presented above, the risk posed by the concentrations of COPCs
remaining in soil at the site is below the 1 x 10-6 target carcinogenic risk for residential
exposure, as well as Indoor Workers and Construction Workers. The non-carcinogenic
Hazard Index was below 1.0 for all scenarios.
The risk posed by the concentrations of COPCs reported in the most recent groundwater
sampling event exceed the 1 x 10-6 target carcinogenic risk for residential exposure, as well
as Indoor Workers and Construction Workers (using the tapwater RSLs). The non-
carcinogenic Hazard Index for groundwater exceeds 1.0.
3.3 Soil-To-Groundwater Pathway Evaluation
Four of the soil COPCs exceeded DAF 20 groundwater protection SSLs. Multiple lines of
evidence indicate that the low levels of soil contamination remaining after excavation is
unlikely to further impact groundwater:
The entire site is covered by concrete and/or asphalt which serves to limit infiltration.
The site soil has been extensively excavated, removing remaining on-site PCE
contamination sources present from previous operations.
Depth of the excavated soil in the possible source areas exceeds 20 feet bgs.
Of the four soil COPCs that exceed DAF 20 SSLs, only one exceeded MCLs in
groundwater (PCE) and one exceeded a VISL (PCE).
4.0 Ecological Risk Assessment
The site is fully developed with buildings containing commercial on the first floor and
residential above. The entire site is covered in concrete and/or asphalt. No surface water
bodies are located on the site or adjoining properties. The current and future use of the site
is commercial and residential with no significant renovations to the current on-site buildings
Risk Evaluation
21st and 21st, Salt Lake City, Utah
July 9, 2025 | Terracon Project No. 61197460
Facilities | Environmental | Geotechnical | Materials 10
expected in the near future. As such, the site is not a viable habitat and cannot be used by
potential ecological receptors as a habitat. Per Utah Administrative Code R315-
101.5.3(a)(8), an Application for a Waiver of an Ecological Risk Assessment has been
prepared and is included as Appendix D.
5.0 Conclusions
Both the carcinogenic risk and the non-carcinogenic Hazard Index for soil exposure are
below the thresholds for residential exposure, as well as Indoor Workers and Construction
Workers. Site risks related to groundwater exposure exceed residential exposure, as well as
Indoor Workers and Construction Workers due to PCE concentrations. However, the risk
values are based on tapwater values, groundwater is approximately 25 feet bgs at the site,
the site is capped with concrete and asphalt, and the probable source contributing to the
groundwater contamination has been removed. Additionally, a VIMS has been incorporated
into building design to mitigate any potential vapor intrusion into new structures. Indoor air
sampling within a commercial space indicated that COPCs were ND, indicating no risk from
soil gas exposure under resident or worker scenarios.
If the site is considered a source of the PCE contamination, it is expected that the PCE
concentrations will continue to decrease over time with some fluctuation.
Due to the soil exposure risk below residential and commercial thresholds, the source of on-
site groundwater contamination being removed, and the incomplete exposure pathway for
both groundwater and soil vapor, Terracon recommends the Site be eligible for a Corrective
Action Complete with Controls designation from DWMRC. Additional requirements for post
construction Site monitoring and reporting will be outlined in an Environmental Covenant
(EC) and Site Management Plan (SMP) prepared for the site.
Risk Evaluation
21st and 21st, Salt Lake City, Utah
July 9, 2025 | Terracon Project No. 61197460
Facilities | Environmental | Geotechnical | Materials 11
6.0 References
Terracon 2025. Fourth Quarterly Groundwater Monitoring Report, 21st & 21st Properties,
2100 South and 2100 East, Salt Lake City, Salt Lake County, Utah. January 6.
Terracon 2024a. Corrective Measures Implementation Report, 21st & 21st Properties, 2145
East 2100 South, Salt Lake City, Salt Lake County, Utah.July 21 Revised October 11.
Terracon 2024b. Vapor Intrusion Mitigation Oversight Services, 21st & 21st Properties, 2145
East 2100 South, Salt Lake City, Utah.October 11.
United States Environmental Protection Agency, Regional Screening Levels for Chemical
Contaminants at Superfund Sites; https://epa-prgs.ornl.gov/cgi-
bin/chemicals/csl_search.
Utah Department of Environmental Quality, Division of Waste Management and Radiation
Control (DWMRC), Technical Guide for Risk Assessments: Utah Administrative Code
R315-101, 2023.
Appendix A
Exhibits
Native Soil:
PCE, Toluene, Chloroform,
Methylene Chloride,
1,1,1-Trichloroethane,
1,1,2,2-Tetrachloroethane,
1,1,2-Trichlorotrifluoroethane,
1,1,2-Trichloroethane,
1,2-Dichloroethane
Soil Gas
Groundwater:
PCE, TCE, Chloroform,
Bromodichloromethane,
cis-1,2-Dichloroethene
Groundwater
Soil Gas:
VOCs
Construction
Worker
Dermal Contact
Ingestion
Inhalation
CONCEPTUAL SITE MODEL
6952 S High Tech Drive
Midvale, Utah 84047
61197460
Employee Resident
Current Use/Future Use
21st and 21st Properties
2145 East 2100 South
Salt Lake City, Utah
Project Manager:
Drawn by:
Checked by:
Approved by:
AST
AA
AA
AST
Exhibit 3
July 2025
Scale:
Project No.
File Name:
Date:
none 3
Exhibit
RECEPTORS
Complete pathway
Incomplete pathway
Soil Dermal Contact
SOURCE INTERACTION
Contamination
Exposure
Medium
Exposure
Route
Ingestion
Appendix B
Data Tables
Contaminant of Potential
Concern (COPC)
Concentration
(µg/kg)
RSL
Residential
RSL
Industrial Risk-based SSL DAF 20 SSL
Tetrachloroethene 5,420 24000 100000 5.1 102
1,1,1-Trichloroethane 91.6 8100000 36000000 2,800 56,000
1,1,2,2-Tetrachloroethane 107 600 2700 0.03 0.6
1,1,2-Trichlorotrifluoroethane 104 6700000 28000000 NE NE
1,1,2-Trichlorethane 103 1100 5000 1.6 32
1,2-Dichloroethane 72 460 2000 1.4 28
Toluene 59.3 4900000 47000000 760 15,200
Methylene Chloride 14.2 57000 1000000 1.3 26
Chloroform 28 320 1400 22 440
NE = screening level not established. All units are presented in µg/kg (micrograms per kilogram).
residential and industrial properties.
Shaded values exceed regulatory screening levels.
Volatile Organic Compounds (VOCs)
DAF 20 SSL: EPA Protection of Groundwater Soil Screening Level Dilution Attenuation Factor times 20.
Risk-based SSL: EPA Protection of Groundwater Risk-based Soil Screening Level SSL.
TABLE 1 MAXIMUM CONCENTRATIONS OF COPCs—Soil
21st and 21st Properties
Salt Lake City, Utah
Terracon Project No. 61197460
EPA RSL:Environmental Protection Agency Regional Screening Levels for soil at residential and industrial properties (November 2024;
TR=1E-06; THQ=1.0).
Contaminant of Potential Concern
(COPC)
Concentration
(mg/l)EPA MCL VISL
Residential
VISL
Commercial
N-Butylbenzene 0.00375J NE NE NE
Chloroform 0.00122J 0.08 0.000814 0.00355
Naphthalene 0.0222J NE 0.00459 0.0201
Tetrachloroethene 2.3 0.005 0.0149 0.0652
NE = screening level not established. All units are presented in mg/l (milligrams per liter).
EPA MCL: Environmental Protection Agency Maximum Contaminant Level for drinking water; November 2024.
Shaded values exceed regulatory screening levels.
EPA VISL: Target Groundwater Concentration (TGC) Vapor Intrusion Screening Level (VISL); November 2024.
TABLE 2 - MAXIMUM CONCENTRATIONS OF COPCs - Groundwater
21st and 21st Properties
Salt Lake City, Utah
Terracon Project No. 61197460
Volatile Organic Compounds (VOCs)
J: The identification of the analyte is acceptable; the reported value is an estimate.
Appendix C
RSL Calculator Outputs
Output generated 07JUL2025:17:00:08
Site-specific 1
Resident Tap Water Inputs
Variable
Resident
Tap
Water
Default
Value
Site-Specific
Value
BW 0-2 (mutagenic body weight) kg 15 15
BW 2-6 (mutagenic body weight) kg 15 15
BW 6-16 (mutagenic body weight) kg 80 80
BW 16-26 (mutagenic body weight) kg 80 80
BW res-a (body weight - adult) kg 80 80
BW res-c (body weight - child) kg 15 15
DFW res-adj (age-adjusted dermal factor) cm 2-event/kg 2610650 2610650
DFWM res-adj (mutagenic age-adjusted dermal factor) cm 2-event/kg 8191633 8191633
EDres (exposure duration - resident) years 26 26
ED0-2 (mutagenic exposure duration first phase) years 2 2
ED2-6 (mutagenic exposure duration second phase) years 4 4
ED6-16 (mutagenic exposure duration third phase) years 10 10
ED16-26 (mutagenic exposure duration fourth phase) years 10 10
EDres-a (exposure duration - adult) years 20 20
EDres-c (exposure duration - child) years 6 6
EFres (exposure frequency) days/year 350 350
EF0-2 (mutagenic exposure frequency first phase) days/year 350 350
EF2-6 (mutagenic exposure frequency second phase) days/year 350 350
EF6-16 (mutagenic exposure frequency third phase) days/year 350 350
EF16-26 (mutagenic exposure frequency fourth phase) days/year 350 350
EFres-a (exposure frequency - adult) days/year 350 350
EFres-c (exposure frequency - child) days/year 350 350
ETres (exposure time) hours/day 24 24
ETevent-res-adj (age-adjusted exposure time) hours/event 0.67077 0.67077
ETevent-res-madj (mutagenic age-adjusted exposure time) hours/event 0.67077 0.67077
ET0-2 (mutagenic dermal exposure time first phase) hours/event 0.54 0.54
ET2-6 (mutagenic dermal exposure time second phase) hours/event 0.54 0.54
ET6-16 (mutagenic dermal exposure time third phase) hours/event 0.71 0.71
Output generated 07JUL2025:17:00:08
Site-specific 2
Resident Tap Water Inputs
Variable
Resident
Tap
Water
Default
Value
Site-Specific
Value
ET16-26 (mutagenic dermal exposure time fourth phase) hours/event 0.71 0.71
ETres-a (dermal exposure time - adult) hours/event 0.71 0.71
ETres-c (dermal exposure time - child) hours/event 0.54 0.54
ET0-2 (mutagenic inhalation exposure time first phase) hours/day 24 24
ET2-6 (mutagenic inhalation exposure time second phase) hours/day 24 24
ET6-16 (mutagenic inhalation exposure time third phase) hours/day 24 24
ET16-26 (mutagenic inhalation exposure time fourth phase) hours/day 24 24
ETres-a (inhalation exposure time - adult) hours/day 24 24
ETres-c (inhalation exposure time - child) hours/day 24 24
EV0-2 (mutagenic events) per day 1 1
EV2-6 (mutagenic events) per day 1 1
EV6-16 (mutagenic events) per day 1 1
EV16-26 (mutagenic events) per day 1 1
EVres-a (events - adult) per day 1 1
EVres-c (events - child) per day 1 1
THQ (target hazard quotient) unitless 0.1 1
IFW res-adj (adjusted intake factor) L/kg 327.95 327.95
IFWM res-adj (mutagenic adjusted intake factor) L/kg 1019.9 1019.9
IRW 0-2 (mutagenic water intake rate) L/day 0.78 0.78
IRW 2-6 (mutagenic water intake rate) L/day 0.78 0.78
IRW 6-16 (mutagenic water intake rate) L/day 2.5 2.5
IRW 16-26 (mutagenic water intake rate) L/day 2.5 2.5
IRW res-a (water intake rate - adult) L/day 2.5 2.5
IRW res-c (water intake rate - child) L/day 0.78 0.78
K (volatilization factor of Andelman) L/m 3 0.5 0.5
LT (lifetime) years 70 70
SA0-2 (mutagenic skin surface area) cm 2 6365 6365
SA2-6 (mutagenic skin surface area) cm 2 6365 6365
Output generated 07JUL2025:17:00:08
Site-specific 3
Resident Tap Water Inputs
Variable
Resident
Tap
Water
Default
Value
Site-Specific
Value
SA6-16 (mutagenic skin surface area) cm 2 19652 19652
SA16-26 (mutagenic skin surface area) cm 2 19652 19652
SAres-a (skin surface area - adult) cm 2 19652 19652
SAres-c (skin surface area - child) cm 2 6365 6365
lsc (apparent thickness of stratum corneum) cm 0.001 0.001
TR (target risk) unitless 1.0E-06 1.0E-06
Output generated 07JUL2025:17:00:08
Site-specific 4
Resident Risk-Based Regional Screening Levels (RSL) for Tap Water
Key: I = IRIS; P = PPRTV; O = OPP; A = ATSDR; T = ATSDR DRAFT; C = Cal EPA; X = PPRTV Screening Level; H = HEAST; D = OW; R = ORD; N = WI; W = TEF
applied; E = RPF applied; G = see user guide; U = user provided; ca = cancer; nc = noncancer; * = where: nc SL < 100X ca SL; ** = where nc SL < 10X ca SL;
SSL values are based on DAF=1; max = ceiling limit exceeded; sat = Csat exceeded.
Chemical
CAS
Number Mutagen?Volatile?
Chemical
Analytical
Type
SFo(mg/kg-day)-1
SFoRef
IUR
(ug/m 3)-1
IUR
Ref
RfD
(mg/kg-day)
RfD
Ref
RfC
(mg/m 3)
RfC
Ref GIABS
Kp(cm/hr)
Butylbenzene, n-104-51-8 No Yes Organics --5.00E-02 U -1 2.25E-01
Chloroform 67-66-3 No Yes Organics 3.10E-02 U 2.30E-05 U 1.00E-02 U 1.95E-03 U 1 6.83E-03
Naphthalene 91-20-3 No Yes Organics 1.20E-01 U 3.40E-05 U 2.00E-02 U 3.00E-03 U 1 4.66E-02
Tetrachloroethylene 127-18-4 No Yes Organics 2.10E-03 U 2.60E-07 U 6.00E-03 U 4.00E-02 U 1 3.34E-02
MW
B
(unitless)
t*
(hr)
τevent
(hr/event)
FA
(unitless)
In
EPD?DAevent (ca)
DAevent(nc child)
DAevent(nc adult)
MCL
(ug/L)
Ingestion
SL
TR=1E-06
(ug/L)
Dermal
SL
TR=1E-06
(ug/L)
Inhalation
SL
TR=1E-06
(ug/L)
Carcinogenic
SL
TR=1E-06
(ug/L)
134.22 1.00E+00 2.29E+00 5.94E-01 1 No --------
119.38 2.87E-02 1.18E+00 4.90E-01 1 Yes 3.16E-04 2.46E-02 4.25E-02 8.00E+01 2.51E+00 2.92E+01 2.44E-01 2.21E-01
128.18 2.03E-01 1.32E+00 5.49E-01 1 Yes 8.16E-05 4.92E-02 8.49E-02 -6.49E-01 1.04E+00 1.65E-01 1.17E-01
165.83 1.65E-01 2.14E+00 8.92E-01 1 Yes 4.66E-03 1.47E-02 2.55E-02 5.00E+00 3.71E+01 6.53E+01 2.16E+01 1.13E+01
Ingestion
SL
Child
THQ=1
(ug/L)
Dermal
SL
Child
THQ=1
(ug/L)
Inhalation
SL
Child
THQ=1
(ug/L)
Noncarcinogenic
SL
Child
THI=1
(ug/L)
Ingestion
SL
Adult
THQ=1
(ug/L)
Dermal
SL
Adult
THQ=1
(ug/L)
Inhalation
SL
Adult
THQ=1
(ug/L)
Noncarcinogenic
SL
Adult
THI=1
(ug/L)
Screening
Level
(ug/L)
1.00E+03 --1.00E+03 1.67E+03 --1.67E+03 1.00E+03 nc
2.01E+02 2.53E+03 4.07E+00 3.98E+00 3.34E+02 3.81E+03 4.07E+00 4.01E+00 2.21E-01 ca
4.01E+02 7.01E+02 6.26E+00 6.11E+00 6.67E+02 1.06E+03 6.26E+00 6.16E+00 1.17E-01 ca
1.20E+02 2.30E+02 8.34E+01 4.06E+01 2.00E+02 3.47E+02 8.34E+01 5.03E+01 1.13E+01 ca
Output generated 07JUL2025:17:00:08
Site-specific 5
Resident Risk for Tap Water
Chemical
SFo(mg/kg-day)-1
SFoRef
IUR
(ug/m 3)-1
IUR
Ref
RfD
(mg/kg-day)
RfD
Ref
RfC
(mg/m 3)
RfC
Ref GIABS
Kp(cm/hr)MW
B
(unitless)
t*
(hr)
τevent
(hr/event)
Butylbenzene, n---5.00E-02 U -1 2.25E-01 134.22 1.00E+00 2.29E+00 5.94E-01
Chloroform 3.10E-02 U 2.30E-05 U 1.00E-02 U 1.95E-03 U 1 6.83E-03 119.38 2.87E-02 1.18E+00 4.90E-01
Naphthalene 1.20E-01 U 3.40E-05 U 2.00E-02 U 3.00E-03 U 1 4.66E-02 128.18 2.03E-01 1.32E+00 5.49E-01
Tetrachloroethylene 2.10E-03 U 2.60E-07 U 6.00E-03 U 4.00E-02 U 1 3.34E-02 165.83 1.65E-01 2.14E+00 8.92E-01
*Total Risk/HI ----------
FA
(unitless)
In
EPD?DAevent (ca)
DAevent(nc child)
DAevent(nc adult)
MCL
(ug/L)
Concentration
(ug/L)
Ingestion
Risk
Dermal
Risk
Inhalation
Risk
Carcinogenic
Risk
Ingestion
Child
HQ
Dermal
Child
HQ
1 No ----3.75E+00 ----3.74E-03 -
1 Yes 3.16E-04 2.46E-02 4.25E-02 8.00E+01 1.22E+00 4.85E-07 4.18E-08 5.00E-06 5.52E-06 6.08E-03 4.82E-04
1 Yes 8.16E-05 4.92E-02 8.49E-02 -2.22E+01 3.42E-05 2.13E-05 1.34E-04 1.90E-04 5.53E-02 3.17E-02
1 Yes 4.66E-03 1.47E-02 2.55E-02 5.00E+00 2.30E+03 6.20E-05 3.52E-05 1.06E-04 2.04E-04 1.91E+01 9.99E+00
------9.67E-05 5.66E-05 2.46E-04 3.99E-04 1.92E+01 1.00E+01
Inhalation
Child
HQ
Noncarcinogenic
Child
HI
Ingestion
Adult
HQ
Dermal
Adult
HQ
Inhalation
Adult
HQ
Noncarcinogenic
Adult
HI
-3.74E-03 2.25E-03 --2.25E-03
3.00E-01 3.07E-01 3.66E-03 3.20E-04 3.00E-01 3.04E-01
3.55E+00 3.63E+00 3.33E-02 2.10E-02 3.55E+00 3.60E+00
2.76E+01 5.67E+01 1.15E+01 6.63E+00 2.76E+01 4.57E+01
3.14E+01 6.06E+01 1.15E+01 6.66E+00 3.14E+01 4.96E+01
Appendix D
Application For A Waiver Of
An Ecological Risk Assessment
Risk Evaluation
21st and 21st, Salt Lake City, Utah
July 9, 2025 | Terracon Project No. 61197460
Facilities | Environmental | Geotechnical | Materials 12
Application for a Waiver of an Ecological Risk Assessment
21st & 21st Properties, 2145 East 2100 South
Salt Lake City, Salt Lake County, Utah
This application is being submitted to request a waiver for performing an ecological risk
assessment at the 21st and 21st Properties Site, located at 2145 East 2100 South (formerly
2100 South 2100 East), Salt Lake City, Utah.
In accordance with the Utah Administrative Code (UAC) R315-101, site investigations must
include an evaluation of human health and ecological risk to support risk-based closure. An
ecological risk assessment is warranted when it has been determined that exposure
pathways are potentially complete for ecological receptors. A complete pathway consists of
1) a source, 2) a mechanism of contaminant release, 3) a receiving or contact medium, 4) a
potential receptor population, and 5) exposure route. Of these five criteria, the most
fundamental is the fourth criterion. In order for a potential receptor population to exist, a
site must contain open areas that would allow plant growth and suitable habitat for wildlife.
Pathways are incomplete for ecological receptors at sites that are completely filled-in with
buildings, concrete, or pavement. For these areas, an ecological risk assessment cannot be
completed.
The 21st and 21st Properties Site is completely paved and/or covered in structures. No
significant areas of vegetation are present, and the site is devoid of suitable habitat for
wildlife. Additionally, the immediate vicinity of the site is residential/commercial, consisting
of paved/concrete lots, commercial businesses, and residential structures (apartment
complexes). The surrounding area contains limited trees and grass (mostly in parking
strips/sidewalk and landscape areas). However, no wildlife at the property has been
observed using the property for permanent habitat or food. Although it is possible that some
species could casually be present (such as birds resting in nearby trees or crossing the
property), it is not plausible that any receptor would forage, nest, or den on the property
itself due to a lack of vegetation.
As any potentially contaminated soil or groundwater is located beneath concrete, structures,
pavement, or transported fill material, all potential areas of habitat are unavailable to
ecological receptors. Since there is no complete exposure pathway, an ecological risk
assessment is not deemed required at this facility and a waiver for conducting a quantitative
ecological risk assessment per R315-101.5.3(a)(8) is requested.