DSHW-2024-006502

May 30, 2024
Mr. Tom Henriod
Rockworth Companies, LLC
4655 South 2300 East, Suite 205
Holladay, UT 84117
RE: Comments to Monitoring Well Installation and Quarterly Groundwater Monitoring Report, April 2024
21st & 21st Properties - 2100 South and 2100 East Salt Lake City, Utah 84109
UTCA-0032
Dear Mr. Henroid:
The Division of Waste Management and Radiation Control (Division) has performed its review of the Monitoring Well Installation and Quarterly Groundwater Monitoring Report, April 2024(Report)
dated May 9, 2024. The Report details the groundwater monitoring well installation and first quarter, 2024 sampling performed at the 21st& 21st Properties (Site) located at 2100 South
2100 East, Salt Lake City, Utah.
Comments pertaining specifically to the Report are included in the attachment to this letter.Please provide a response to the attached comments by July 15, 2024.
In addition to the attached, specific comments on the Report, the Division has identified several other issues related to the Site.
The Division understands that a Corrective Measures Implementation Report (CMIR) is in development, outlining the completed tasks specified in the March 2021 Remedial Action Plan (RAP).
The Report indicates in Section 5.0 that the Vapor Intrusion Mitigation System (VIMS) was installed at the Site, the source was removed, and contaminated soil was excavated and taken
off-site in accordance with the RAP. As of the date of this letter, the Division has not received the CMIR and cannot verify the actions described in the Report.Please provide the CMIR
by July 1, 2024.
It is the Division’s understanding that the Revised Site Management Plan (SMP) Outline (Outline) submitted February 17, 2022 (and as provided in Appendix D of the Report), outlines the
installation of monitoring wells and monitoring requirements for the Site. Additionally, the Outlinehighlights the steps to be taken if contaminant action limits are exceeded and if
commercial land use exceedances are identified.According to Section 5.0 of the Report, data from all on-site monitoring wells (MW-1A, MW-4, and MW-5) exceed the Environmental Protection
Agency (EPA) Commercial Vapor Intrusion Screening Level (VISL) for tetrachloroethene (PCE). Additionally, the monitoring well on the off-Site property to the west (MW-2A) exceeds the
EPA Commercial VISL for PCE as well. Based on the requirements set forth in the Outline, additional investigationis required.
The Division is aware that the installation of the VIMS was proposed in the RAP. However, the Outline indicates that if a Cancer Risk of 1E-04 or greater and a hazard index of 1 or greater
are identified in on-site monitoring wells,“Terracon must prove that the VIMS is protective for this risk range.” Per the Outline, the following must be performed for four consecutive
quarters to ensure the VIMS is adequately mitigating the vapor intrusion pathway:
The VIMS exhaust pipes should be sampled for the Contaminants of Concern (COCs) that include PCE, trichloroethylene (TCE), cis-1,2-dichloroethene (cis-DCE), 1,1-dichloroethylene (1,1-DCE),
and vinyl chloride.
Permanent sub-slab vapor points should be installed and sampled for COCs.
Indoor air sampling for COCs should be performed in tandem with the sub-slab vapor sampling. Evaluation of the efficacy of the VIMS must address cumulative risk to the commercial receptor,
not just individual contaminant risk.
The Report indicates the Commercial VISL for PCE was exceeded at MW-2A. This exceedance triggers additional investigation of potential off-stie impactsper the Outline. Soil gas sampling,
in accordance with the Outline,must be performed to assess whether COCs pose a potential risk to the property associated with MW-2A, and areas west of the Site.
Please provide the Additional Investigation Work Plan (Work Plan), assessing contamination and exposure pathways at the Site as described in the Outline by August 1, 2024.
If you have any questions, please call Ethan Upton at [phone].
Sincerely,
Paige Walton, Program Manager Corrective Action
Division of Waste Management and Radiation Control
PW/EAU/
Enclosure:
c:Dorothy Adams, Interim Health Officer, Salt Lake County Health Dept.
Ron Lund, Environmental Health Director, Salt Lake County Health Dept.
Eric Peterson, Environmental Health Deputy Director, Salt Lake County Health Dept.
Eileen Brennan, Division of Environmental Response and Remediation, ([e-mail])
Andrew Turner, Terracon Consultants, Inc. ([e-mail])
Tom Henroid, Rockworth Companies ([e-mail])
Division Comments on theMonitoring Well Installation and Quarterly Groundwater Monitoring Report, April 2024
Throughout the Monitoring Well Installation and Quarterly Groundwater Monitoring Report, April 2024 (Report) for the 21st & 21st Properties (Site) located at 2100 South 2100 East, Salt
Lake City, Utah, reference is made to MW-1 through MW-3. As noted in Section 1.1 of the Report, MW-1 through MW-3 had production issues and replacement wells MW-1A through MW-3A were
installed in January 2024. The Report does not refer to the replacement well numbers, which creates confusion as to which wells were sampled. Revise the Report in its entirety to refer
to the correct well numbers, e.g., MW-1A, MW-2A, and MW-3A, consistent with the well logs in Appendix C.
Section 1.1 of the Report indicates that new monitoring wells were constructed due to the inability to sample the original monitoring wells on-Site (MW-1, MW-2, and MW-3). However, the
Report does not indicate whether the original wells were abandoned or destroyed before or during the redevelopment of the Site. Update the Report to indicate the status of the original
three monitoring wells. If the monitoring wells are still active update the figures to include their location.
Section 1.1 indicates that the outline was submitted to Dale Urban on February 17, 2024. Please clarify the Outline was provided in 2022.
The installation of five monitoring wells (MW-1A, MW-2A, MW-3A, MW-4, and MW-5) was proposed in the Revised Site Management Plan (SMP) Outline (Outline). However, the construction details
were not proposed in the Outline or discussed with the Division of Waste Management and Radiation Control (Division). Section 1.2 of the Report outlines the monitoring well installation
and construction which includes all five wells installed to approximately 40 feet below land surface (ft bls) and screened from 20 to 40 ft bls. Several uncertainties arise with the
increase inmonitoring well screen length most notablycontamination location andmobilization through the lithology. Please revise the Report to include uncertainties and rationale of
the chosen well construction methodology.

Section 1.2 indicates the newly installed monitoring wells were developed using a surge block and bailer until geochemical parameters were stabilized with a minimum of six “purge volumes”
extracted from each monitoring well. During the Division’s samplingobservationon March 31, 2024, the purge water from the observed wells appeared highly turbid. The stabilization criteria
used to determine if the monitoring wellswerefully developed was not discussed in the Report. Additionally, “purge volumes” and the total development volume are not detailed in the Report.
Please discuss what parameters and stabilization criteria were used for development. Additionally, define purge volumes and include the well development logs in the Report so calculations
may be verified.
Sections 1.2 and 2.1 indicate that purge water from the development and sampling of new wells was spread on-Site and allowed to infiltrate into the ground.The Division does not practice
thin spreading withoutgenerator knowledge. Additionally, if generator knowledge is known and thin spreading is practiced, the water extracted from the wells should never be allowed to
leave the Site or infiltrate into the ground. Thin spreading should be performed on an impervious surface to allow known contaminants of concern to volatilize without being reintroduced
into the subsurface. Please provide justification, e.g., historical waste analysis data, for handling investigation derived waste in this manner.
Section 1.3 of the Report states MW-4 was unable to be surveyed due to “considerable large debris located on top of the well.”As the well was installed in January 2024, it is unclear
the source of this debris. Please indicate if MW-4 will be surveyed and when the survey will occur so that it may be included in future groundwater elevation measurements. The Division
understands that the survey of the monitoring wells was collected off an “arbitrary semi-permanent on-site benchmark.” If this method is used to survey monitoring well elevations, MW-4
should be measured based on the same benchmark as the monitoring wells that were previously surveyed. If the same benchmark cannot be utilized, it is recommended that all monitoring
wells on-Site be resurveyed.
Section 2.1 of the Report outlines the sampling procedure used to sample all five monitoring wells at the Site. The Report indicates the monitoring wells were purged and sampled using
a bailer. However, there are no decontamination procedures discussed in the Report for how the equipment used to sample was decontaminated in between monitoring wells.Update the Report
to discuss the decontamination procedures and efforts to reduce cross-contamination for the water level meter and bailer used during sampling. If a new bailer and twine was used for
each monitoring well, please update the Report accordingly.
The Report outlines the use of a bailer to sample the monitoring wells. During the Division’s observation of sampling on March 31, 2024, Terracon personnel stated that the groundwater
was too deep to perform low-flow sampling using aperistaltic pump. The Division suggests sampling via low-flow sampling procedure to obtain the most accurate, representative groundwater
sample possible at the Site. Please update the Report with rationale of using a bailer rather than a peristaltic pumpfor this sampling event and the plannedsampling procedure for future
groundwater monitoring events using the low-flow method.
Section 2.1 of the Report states that prior to sampling, geochemical parameters (temperature, pH, specific conductivity, dissolved oxygen, and oxygen reduction potential) were collected
until stability was achieved or three volumes were purged from the monitoring wells. However, the Report does not define whatgroundwater parameter values are used to determine stabilizationor
what constitutes a “volume” (i.e. well volume, boring volume, equipment volume).Please provide the well volume calculations and groundwater sampling forms demonstrating stability of
groundwater geochemical parameters or sufficient well purge volumes.
Section 2.2 indicates groundwater elevations ranged from 67.22 to 77.22 feet above mean sea level. The Division understands that a survey was performed using an arbitrary benchmark rather
than a benchmark with a known elevation above mean sea level. Based on the relative elevation of the Site, the groundwater elevations are not likely representative of actual feet above
mean sea level and should be reported accordingly throughout the report, in the figures, and in Table 1.
Section 5.0 indicates that the off-Site well, MW-2A, exceeds the commercial vapor intrusion screening level (VISL) for tetrachloroethylene (PCE). As noted in Exhibit 2, MW-2A is located
near a building (northwest corner of 2100 S and 2100 E). It appears that the extent of the groundwater plume has not been defined in this direction. Discuss the potential for vapor intrusion
issues in this building. Also clarify if the owner of the building has been notified of potential vapor intrusion issues due to impacted groundwater underlying the building.
The Outline provided in Appendix D indicates the on-Site monitoring action levels are based on a cancer risk of 1E-04 or greater and a hazard index of 1 or greater. However, in order
to enter into an SMP, the total (cumulative) cancer risk must be shown to be within the acceptable cancer risk range of 1E-04 to 1E-06 and equal to or below a hazard indexof one, as
defined in Utah Administrative Code R315-101. While use of the action levels (VISLs) provides a gauge as the magnitude of residual contamination, individual comparison is not acceptable,
but rather total risk and hazard must be determined.
The Utah Division of Environmental Response and Remediation (DERR) Leaking Underground Storage Tank (LUST) located in the southwest portion of the Site was discussed in Section 5.0 of
the Report. The DERR LUST regulatory requirements and regulationsdo not fall under theDivision’s Environmental Cleanup Program (ECP) and are not governed under the requirements ofUtah
Administrative CodeR315-101 which establishes the requirements for the Sites under in the ECP. As such, the DERR LUST at the Site should not be included in the Report. Additionally,
DERR initial screening levels (ISLs), Tier 1 screening levels,and Utah groundwater quality standards should not be listed in the Tables or used to scrutinize analytical results as they
are not relevant to Utah Administrative CodeR315-101. Please update the report accordingly.