DSHW-2024-004979

March 1, 2024
Terry R. Etter
Corporate Environmental Affairs
Unisys Corporation
3199 Pilot Knob Road
Eagan, MN 55121
RE: Site Management Plan
Unisys Salt Lake City Facility
322 North 2200 West, Salt Lake City, Utah
EPA ID: UTD009073214
Dear Mr. Etter:
The Division of Waste Management and Radiation Control conducted a 30-day public comment period on theproposed Site Management Plan prepared by Geosyntec Consultants and dated January
2024 for the Unisys site in Salt Lake City, Utah.
The comment period ended on February 28, 2024. No public comments were received. The Site Management Plan is hereby approved for implementation.
The next step of the required site management activities is to place an environmental covenant on the impacted property. Unisys needs to work with L3 Harris and Drawbridge Realty to
develop a draft environmental covenant for review and approval of the Division by June 30, 2024.
If you have any questions, please contact Hao Zhu at 801-558-9833 or email [e-mail].
Sincerely,
Douglas J Hansen, Director
Division of Waste Management and Radiation ControlDJH/HZ/wac: Angela Dunn, Health Officer, Salt Lake County Health Dept. Dorothy Adams, Deputy Director, Salt Lake County Health Dept.
Ron Lund, Environmental Health Director, Salt Lake County Health Dept. Brian Smith, Geosyntec Consultants (Email) [e-mail] Etter, Unisys Corporation (Hard Copy and Email)[e-mail]
Carmeli, L3 Harris (Email) [e-mail] Embree, Drawbridge Realty (Email) [e-mail]
.
Division of Waste Management and Radiation Control
Comments on Groundwater Vapor Intrusion Risk Evaluation Update
Unisys Salt Lake City Facility
EPA ID# UTD009073214
Exposure Point Concentrations
EPA memorandum dated March 11, 2014, provided guidance on the determination of groundwater exposure point concentration (GW EPC) to be used in risk assessment, (OSWER Directive 9283.1-42,
February 2014).
The guidance document defines GW EPC as a conservative estimate of the average chemical concentration in groundwater at a potential location and point in time. The guidance goes further
to outline a recommended approach for estimating a GW EPC for use in evaluating risk posed by reasonable maximum exposure conditions at sites with contaminated groundwater. The recommended
approach is intended to improve the quality and consistency of calculating EPCs for groundwater in risk assessments performed at EPA’s Superfund and RCRA corrective action sites.
Please follow the recommended approach to determine the GW EPC to be used in the risk assessment calculations.
Also, please provide to the Division a groundwater plume diagram as it exists at the Unisys site with locations of all the wells in the plume and with clearly defined boundaries.
Groundwater Screening Levels
In calculating indoor air concentration and VISL target groundwater concentration, Unisys assumed a target risk (TR) of 1x10-5 and a hazard quotient (HQ) of one rationalizing that the
TR was the midpoint of the acceptable risk range or risk management range.
Please note that the assumed TR is not consistent with R315-101. The point of departure (POD) for risk assessment evaluation as identified in R315-101 is 1x10-6 and not 1x10-5. The POD
is defined as the TR at which risk to an individual is considered insignificant. All risk-based concentrations are evaluated at this TR.
Please recalculate the VISL target ground water concentrations using a TR of 1x10-6.
Risk Calculation
The equation used in calculating cumulative cancer risk contains a TR 0f 1x10-5. As discussed in Comment Number 2 above, please revise your equation to be consistent with the TR identified
in R315-101 by using a TR=1x10-6.
Conclusions
Depending on the revised risk calculations, the conclusion section may need to be revised.
Lower Zone of Shallow Aquifer:
Monitoring well MW-8B is screened in the shallow aquifer at a depth of 17-22 feet below the ground surface. TCE was detected in MW-8B at a concentration of 240 ug/L during the 2022 groundwater
monitoring event. The 2022 monitoring event also detected TCE in well MW-8A which was screened at depth around 10 feet at a concentration of 3.3 ug/L and nested with well MW-8B.
In the evaluation of indoor air vapor intrusion risk, the lower TCE concentration detected at a shallower depth of the nested wells was used in the evaluation without consideration of
the higher detected TCE concentration at deeper depth.
In reference to the EPA Guidance Document on determination of groundwater exposure point concentration, (see Comment Number 1), please justify why the higher TCE concentration was not
considered in the risk evaluation.
Attachment B EPA VISL Output Spreadsheet.
Please include the VISL Output as presented in the VISL Calculator showing the cumulative cancer risk and the hazard index. The output table presented in Attachment B of the report is
missing that information.