DSHW-2024-005508

DSHW-2024-005508 195 North 1950 West • Salt Lake City, UT
Mailing Address: P.O. Box 144880 • Salt Lake City, UT 84114-4880
Telephone [phone] • Fax [phone] • T.D.D. 711
www.deq.utah.gov
Printed on 100% recycled paper
State of Utah

SPENCER J. COX
Governor

DEIDRE HENDERSON
Lieutenant Governor
Department of
Environmental Quality

Kimberly D. Shelley
Executive Director

DIVISION OF WASTE MANAGEMENT
AND RADIATION CONTROL

Douglas J. Hansen
Director

March 29, 2024

Kris Blauer, Manager Environmental Services
Northrop Grumman Systems Corporation
P.O. Box 707
Brigham City, UT 84302-0707

RE: Groundwater Flow and Contaminant Transport Model Update
Post-Closure Permit
ATK Launch Systems LLC. – Promontory
Northrop Grumman Systems Corporation
EPA ID UTD009081357

Dear Mr. Blauer:

The Division of Waste Management and Radiation Control (Division) has completed a review of a report of
the Groundwater Flow and Contaminant Transport Model Update (Model Update) dated December 2023 and
prepared by Geosyntec for the ATK Launch Systems LLC. (ATK) – Promontory Facility. The Model
Update is a part of the requirements of the facility’s Post-Closure Permit to support decisions related to
assessing risk to human health and the environment.

The Model Update includes recalibrations of the input parameters; e.g., transport properties and the source
terms of perchlorate and trichloroethene present in the subsurface for contaminant transport modeling at the
facility. The contaminant transport model was based on the 2018 groundwater flow modeling outputs.
It appears that the 2023 recalibrated model simulates a good match against the historical observed
concentrations of perchlorate and trichloroethene at the site. The Model Update also includes future
prediction of contaminant transport at Pipe Springs and the footprint of the groundwater plumes. It is likely
that the concentrations of perchlorate and trichloroethene will continue increasing over time in the future at
the spring areas consistent with past field sampling results.

Based on the Division’s review, the 2023 Model Update appears to be acceptable and is hereby approved.

In accordance with Condition V.E.2. of the Post-Closure Permit, ATK is required to recalibrate the
groundwater flow and solute transport model annually. Based on the previous model calibrations and
simulations, it appears that an annual model update may not be necessary for the site. Therefore, ATK may
request for a less frequent model recalibration through an appropriate permit modification in the future.
(Over)

If you have any questions, please call Hao Zhu at 801-558-9833 or Karen Wallner at 385-499-0218.

Sincerely,

Douglas J. Hansen, Director
Division of Waste Management and Radiation Control

DJH/HZ/wa

c: Dorothy Adams, Interim Director, 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.
Jesse Newland, U.S. EPA, Region VIII
Brian Smith, Geosyntec Consultants (Email)
Blair Palmer, Northrop Grumman Systems Corporation (Email)
Tim Jimenez, Northrop Grumman Systems Corporation (Email)
Kris Blauer, Northrop Grumman Systems Corporation (Email and Hard Copy)
Karen Wallner, Division of Waste Management and Radiation Control, UDEQ