DSHW-2008-024786 - 0901a068801e1f36

David P. Gosen, P.E.
Director, Environmental Services
ATK Launch Systems – Promontory
P.O. Box 707
Brigham City, UT 84302-0707

RE: Review of the Groundwater Flow and Contaminant Transport Models Report
ATK Launch Systems - Promontory Facility
EPA I.D. #UTD009081357

Dear Mr. Gosen:

The Division of Solid and Hazardous Waste has completed its review of the Groundwater Flow and Contaminant Transport Models Report that was submitted to our office on January 8, 2008.
Thank you for revising the original model by incorporating the perched aquifer zone and addressing the other issues as requested. Our review of the current models and report has raised
some additional comments that are enclosed with this letter.

The Division is encouraged that the models can be approved once these issues are resolved. Please submit a response to the questions and comments within 45 days of receipt of this letter.
Thank you for your cooperation. If you have any questions, please contact Jeff Vandel at 538-6170.

Sincerely,
ORIGINAL DOCUMENT SIGNED BY SCOTT T. ANDERSON FOR DENNIS R. DOWNS ON 4/4/08
Dennis R. Downs, Director
Utah Division of Solid and Hazardous Waste

DRD\JV\tjm

Enclosure

c: Paul Hancock, ATK Launch Systems
Nancy Morlock, USEPA Region VIII

Comments on the Groundwater Flow and Contaminant Transport Model (Revised)
ATK Launch Systems - Promontory Facility, January 2008

Section 3.2, Flow modeling Software, p. 3-3, and Section 4.5, Grid, p.4-6: The text states that a uniform grid (one node every 200 feet) was selected for the entire modeling domain.
While this approach can be justified for the flow model, the transport model could have benefited from either a grid refinement or a domain resizing, especially in zones where calibration
problems were encountered (e.g., areas of fracture flow, see p.4-8). Please explain why a grid refinement for the transport portion of the model was not contemplated.

Section 3.5.3, Recharge, p. 3-6: The text states that a recharge value of three inches/year into the uppermost, active layer was determined during the calibration runs. Was this value
arrived by trial and error, or by a more numerically, objective “goal search” routine, such as implemented in PEST? Please elaborate.

Section 3.6.1, Calibration Process, p.3-9: The text mentions that the target maximum head change criterion of 0.1 foot (as stated in the original work plan) was not achieved; however,
multiple simulation runs demonstrated that the flow model solution was stable and therefore acceptable. Please explain how that was done in practice, e.g., was the same (or approximately
the same) solution obtained with different numerical solvers (SIP, SOR, PCG, AMG, etc.), and were different damping factors employed?

Section 3.6.3, Calibration Results, p. 3-13: The text states that the greatest head differences between the predicted, steady state, and measured potentiometric surfaces were encountered
in the perched aquifer, with a maximum drawdown of 27 feet in the final iteration. It appears to us that more data from that area (i.e., one or two monitoring wells) might be desirable
(especially to the east of J-2, the east of J-3, and the northeast of J-4), as contaminant plumes for both TCE and perchlorate still seem to be undefined (i.e., not delineated satisfactorily).

Section 4.2, Transport Parameters, p 4-2: The text states that, because monitoring reportedly demonstrated that perchlorate has degraded in the manufacturing area and downgradient of
the leach field, a decay rate (first-order) of 0.00065 1/day was determined for modeling purposes. However, later in the text it is stated that because Visual Modflow does not allow
the decay rate to be varied with time, a decay rate was not used (instead, source concentrations were varied over time). Please clarify.

Section 4.3, Sources and Sinks, p. 4-3: There appears to be a typographical error in the text. Please clarify the sentence “. . . , this difference in constant concentration values
between resulted in the unreasonable situation of removing . . .”

Figures: Calibration, “goodness-of-fit” charts appear to be missing. Please attach the relevant calibration charts of observed vs. final, calibrated heads for the modeling domain layers
(both for the flow model, as well as for the transport model).

April 4, 2008

288 North 1460 West • Salt Lake City, UT
Mailing Address: P.O. Box 144880 • Salt Lake City, UT 84114-4880
Telephone [phone] • Fax [phone] • T.D.D. [phone]
www.deq.utah.gov
TN200800258

State of Utah

Department of Environmental Quality

Richard W. Sprott
Executive Director

DIVISION OF SOLID AND HAZARDOUS WASTE
Dennis R. Downs
Director

JON M. HUNTSMAN, JR.
Governor

GARY HERBERT
Lieutenant Governor