DERR-2024-012256

Stantec Consulting Services Inc.
2890 East Cottonwood Parkway; Ste 300
Salt Lake City, UT 84121
Tel: [phone]

December 24, 2020

2196 Pink Coral Circle
Cottonwood, UT 84121

RE: Indoor Air Investigation
Dear :
As you are aware, Stantec Consulting Services Inc. (Stantec) has been retained by Praxair Distribution, Inc.
(PDI) to conduct semi-annual testing of indoor air quality within your basement, as well as the sub-slab soil
gas mitigation system’s off-gas emission, as directed by and coordinated with the Utah Department of
Environmental Quality (UDEQ). I am writing to provide you with a summary of the most recent test results.

On November 18, 2020, Stantec collected an indoor air sample from your basement using one (1) 6-liter,
stainless-steel, laboratory-certified, SummaTM-type canister, equipped with a 24-hour flow rate controller
provided by the Utah-certified, analytical laboratory, ALS Environmental. After a sampling timeframe of
approximately 24 hours, Stantec returned to your home to close the canister valve and retrieve the canister
for delivery to the laboratory. Likewise, we also collected an air sample representative of off-gas emissions
associated with the sub-slab soil gas mitigation system that discharges to the atmosphere atop your
residence’s roof.

Immediately upon sample collection, the air samples were labeled and hand-delivered to the laboratory for
quantitative analyses. All sampling activities and delivery of the samples to the laboratory were conducted
under strict Chain-of-Custody (CoC) and Quality Assurance/Quality Control (QA/QC) protocol. Copies of
the actual laboratory result reports are submitted to the UDEQ and are available upon request to Stantec.
INDOOR AIR SAMPLING RESULTS
The following table presents a summary of laboratory results for historical indoor air samples collected
within your basement and analyzed by Method EPA TO-15 for Trichloroethylene (TCE, aka
trichloroethene). The laboratory utilizes a Single Ion Mode (SIM) analysis for the indoor air samples to
ensure that the Method Detection Limit (MDL) for TCE is below the US EPA's Residential Indoor Air Vapor
Intrusion Screening Level (VISL) concentration of 0.48 micrograms per cubic meter (µg/m3). The TCE VISL
serves as the UDEQ Action Level and may be used as a benchmark, indicating that supplemental
investigation and/or possible mitigation might be warranted, if exceeded.

Sample Name Date Collected TCE Concentration (µg/m3)
Basement A 12/3/12 < 0.16
Basement A 1/24/13 0.24
Basement A 4/9/13 < 0.27
Indoor A 8/13/13 < 0.27
Indoor A 11/8/13 < 0.27
Indoor A 3/28/14 < 0.27
Indoor A 10/25/14 < 0.27
December 24, 2020
Page 2 of 3

Indoor A 5/1/15 < 0.27
Indoor A 11/13/15 <0.27
Indoor A 6/1/16 < 0.27
Indoor A 1/31/17 < 0.27
Indoor A 8/30/17 < 0.27
Indoor A 3/1/18 < 0.27
Indoor A 9/21/18 <0.27
Indoor A 3/8/19 <0.27
Indoor A 9/17/19 < 0.27
Indoor A 5/7/20 <0.27
Indoor A 11/18/20 <0.27
US EPA VISL* 0.478
*VISL = Residential Vapor Intrusion Screening Level for Indoor Air THQ=1 (µg/m3)
3.2 MITIGATION SYSTEM - ATMOSPHERIC OFF-GAS, AIR SAMPLING RESULTS
The following table is a summary of laboratory results for TCE concentrations in the outside off-gas, air
emission samples analyzed by Method EPA TO-15:
Sample Name Date Collected TCE Concentration (µg/m3)
Outflow A 12/4/12 130
Outflow A 1/7/13 40
Outflow A 2/6/13 25
Outflow A 5/3/13 27
Outflow A 8/9/13 37
Outflow A 11/8/13 30
Outflow A 3/27/17 30
Outflow A 10/24/14 30
Outflow A 5/1/15 23
Outflow A 11/13/15 24
Outflow A 6/1/16 23
Outflow A 12/6/16 24
Outflow A 8/30/17 31
Outflow A 3/1/18 14
Outflow A 9/21/18 23
Outflow A 3/8/19 11
Outflow A 9/17/19 15
Outflow A 5/7/20 18
Outflow A 11/18/20 7.8
December 24, 2020
Page 3 of 3

UDAQ Toxic Screening Level (TSL)* 597
*TSL = Toxic Screening Level for TCE Hazardous Air Pollutant (HAP)
According to the UDEQ, the TSL for TCE does not constitute a standard or Action Level which a source's
emissions to the atmosphere cannot exceed. Rather, TSLs are screening levels above which the UDEQ has
determined that additional information should be obtained to substantiate that the model-predicted
concentration would not expose sensitive individuals, animals, or vegetation to unnecessary health risks.

SUMMARY CONCLUSIONS

TCE was not detected during the most recent sampling event (the Method Detection Limit concentration
<0.27 µg/m3 is well below the US EPA VISL 0.478 µg/m3). Data to date indicate that continued use of the
sub-slab soil gas mitigation system beneath your residence should provide continued, appropriate
protection to indoor air within your residence.

If you have questions or concerns, please contact me at [phone] or the UDEQ Project Manager, Mr.
Joseph Katz, at [phone].
Respectfully
Stantec Consulting Services Inc.

John G. Russell, III, CPG
Sr. Hydrogeologist, Environmental Risk Manager

c. J. Katz/UDEQ
J. Pacuska/PDI
R. Pratt/R. Foye/Stantec

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Stantec Consulting Services Inc.
2890 East Cottonwood Parkway; Ste 300
Salt Lake City, UT 84121
Tel: [phone]

December 24, 2020

2202 Pink Coral Circle
Cottonwood, UT 84121

RE: Indoor Air Investigation
Dear
As you are aware, Stantec Consulting Services Inc. (Stantec) has been retained by Praxair Distribution, Inc.
(PDI) to conduct semi-annual testing of indoor air quality within your basement, as well as the sub-slab soil
gas mitigation system’s off-gas emission, as directed by and coordinated with the Utah Department of
Environmental Quality (UDEQ). I am writing to provide you with a summary of the most recent test results.

On November 18, 2020, Stantec collected an indoor air sample from your basement using one (1) 6-liter,
stainless-steel, laboratory-certified, SummaTM-type canister, equipped with a 24-hour flow rate controller
provided by the Utah-certified, analytical laboratory, ALS Environmental. After a sampling timeframe of
approximately 24 hours, Stantec returned to your home to close the canister valve and retrieve the canister
for delivery to the laboratory. Likewise on this date, we also collected an air sample representative of off-gas
emissions associated with the sub-slab soil gas mitigation system that discharges to the atmosphere atop
your residence’s roof.

Immediately upon sample collection, the air samples were labeled and hand-delivered to the laboratory for
quantitative analyses. All sampling activities and delivery of the samples to the laboratory were conducted
under strict Chain-of-Custody (CoC) and Quality Assurance/Quality Control (QA/QC) protocol. Copies of
the actual laboratory result reports are submitted to the UDEQ and are available upon request to Stantec.
INDOOR AIR SAMPLING RESULTS
The following table presents a summary of laboratory results for historical indoor air samples collected
within your basement and analyzed by Method EPA TO-15 for Trichloroethylene (TCE, aka
trichloroethene). The laboratory utilizes a Single Ion Mode (SIM) analysis for the indoor air samples to
ensure that the Method Detection Limit (MDL) for TCE is below the US EPA's Residential Indoor Air Vapor
Intrusion Screening Level (VISL) concentration of 0.478 micrograms per cubic meter (µg/m3). The TCE
VISL serves as the UDEQ Action Level and may be used as a benchmark, indicating that supplemental
investigation and/or possible mitigation might be warranted, if exceeded.

Sample Name Date Collected TCE Concentration (µg/m3)
Basement B 12/3/12 1.3
Basement B 1/7/13 0.62
Basement B 4/4/13 0.39
Indoor B 8/13/13 < 0.27
Indoor B 11/8/13 0.40
Indoor B 3/28/14 < 0.27
Indoor B 10/25/14 < 0.27
December 24, 2020
Page 2 of 3

Indoor B 5/1/15 < 0.27
Indoor B 11/13/15 < 0.27
Indoor B 5/27/16 < 0.27
Indoor B 12/13/16 < 0.27
Indoor B 8/30/17 < 0.27
Indoor B 3/1/18 < 0.27
Indoor B 9/21/18 <0.27
Indoor B 3/8/19 <0.27
Indoor B 9/17/19 < 0.27
Indoor B 5/7/20 <0.27
Indoor B 11/18/20 <0.27
US EPA VISL* 0.478
*VISL = Residential Vapor Intrusion Screening Level for Indoor Air THQ=1 (µg/m3)

MITIGATION SYSTEM - ATMOSPHERIC OFF-GAS, AIR SAMPLING RESULTS
The following table is a summary of laboratory results for TCE concentrations in the off-gas, air emission
samples analyzed by Method EPA TO-15:
Sample Name Date Collected TCE Concentration (µg/m3)
Outflow B 12/4/12 48
Outflow B 1/7/13 17
Outflow B 2/6/13 7.5
Outflow B 5/3/13 12
Outflow B 8/9/13 19
Outflow B 11/8/13 12
Outflow B 3/27/14 7.3
Outflow B 10/24/14 13
Outflow B 5/1/15 6
Outflow B 11/13/15 8.9
Outflow B 5/27/16 6.9
Outflow B 12/13/16 4.0
Outflow B 8/30/17 11.0
Outflow B 3/1/18 4.2
Outflow B 9/21/18 6.4
Outflow B 3/8/19 2.0
Outflow B 9/17/19 4.6
Outflow B 5/7/20 4.2
Outflow B 11/18/20 3
December 24, 2020
Page 3 of 3

UDAQ Toxic Screening Level (TSL)* 597
*TSL = Toxic Screening Level for TCE Hazardous Air Pollutant (HAP)

According to the UDEQ, the TSL for TCE does not constitute a standard or Action Level which a source's
emissions to the atmosphere cannot exceed. Rather, TSLs are screening levels above which the UDEQ has
determined that additional information should be obtained to substantiate that the model-predicted
concentration would not expose sensitive individuals, animals, or vegetation to unnecessary health risks.

SUMMARY CONCLUSIONS

TCE was not detected during the most recent sampling event (the Method Detection Limit concentration
<0.27 µg/m3 is well below the US EPA VISL 0.478 µg/m3). Data to date indicate that continued use of the
sub-slab soil gas mitigation system beneath your residence should provide continued, appropriate
protection to indoor air within your residence.

If you have questions or concerns, please contact me at [phone] or the UDEQ Project Manager,
Mr. Joseph Katz, at [phone].
Respectfully
Stantec Consulting Services Inc.

John G. Russell, III, CPG
Sr. Hydrogeologist, Environmental Risk Manager

c. J. Katz/UDEQ
J. Pacuska/PDI
R. Foye/R. Pratt/Stantec

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