DSHW-2007-007555 - 0901a06880162db5

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

RE: Revisions to the Draft Groundwater Flow and Transport Model, ATK Launch Systems - Promontory Facility, EPA I.D. #UTD009081357

Dear Mr. Gosen:

On June 19, 2007, Helge Gabert and Jeff Vandel of my staff held a conference call with Paul Hancock and Kris Blauer of EarthFax Engineering regarding the status of the groundwater flow
and transport model on which ATK has been working. This letter is intended to summarize and document the discussion that was held.

ATK first submitted a work plan for the groundwater model in June of 2004. After revisions were made to the work plan, the work plan was approved on October 14, 2004. ATK submitted
the completed model to the Division on February 9, 2006. Upon review of the model by the Division, comments and questions on it were provided to ATK in July, 2006. ATK submitted its
response to the Division’s comments and questions on October 10, 2006 and then a meeting was held at the office of EarthFax engineering on November 29, 2006 to discuss some of the issues
concerning the model. The meeting resulted in an agreement that ATK and EarthFax would make some adjustments to the model as recommended by the Division. Other than a few informal
inquiries as to the status of the work on the model, no other communications occurred regarding the model until the conference call referenced above was held.

Based on the conference call discussion, it was determined that three primary adjustments to the model, as discussed previously, still needed to be completed. These adjustments should
be made to prepare an alternative groundwater flow and transport model which incorporates the following three features:

a sloped interface between layers three and four along the eastern model domain, reflecting the fractured/unfractured bedrock contact, as observed and documented in groundwater monitoring
well logs from that area;

a perched aquifer, also along the eastern model domain, reflecting boundary conditions other than constant head cells. For the transport simulation, either Neumann or Cauchy-type boundary
conditions should be implemented for this area; and,

a sensitivity analysis for all contaminant parameters (TCE, perchlorate, TCA, and DCE.

Statistical, goodness-of-fit, charts should be presented for both the flow (calculated vs. observed heads) and transport (calculated vs. observed concentrations) portions of the alternative
model vs. the original model. The report should then recommend the appropriate model (original or alternative) to be approved.

Since the progress of the corrective action process for groundwater at the Promontory facility is tied to the approval of the groundwater model (Draft Post-Closure Permit, Conditions
V.A.2. and V.A.3.), the Division will now require that the alternative model and other information as described above be submitted to the Division in a report no later than 45 days after
the Post-Closure Permit is issued. Draft permit condition V.A.2 will be modified to include this requirement prior to the 45-day public comment period. It is anticipated that the comment
period will begin on July 2, 2007.

Thanks for your cooperation on this matter. If you have any questions, please contact Jeff Vandel at [phone].

Sincerely,

ORIGINAL DOCUMENT SIGNED BY DENNIS R. DOWNS ON 6/25/07

Dennis R. Downs, Executive Secretary
Utah Solid and Hazardous Waste Control Board

DRD\JV\tm

c: Paul Hancock, ATK Launch Systems

File to: ATK Launch Systems - Promontory

June 25, 2007
Page 2
TN200700755

June 25, 2007

TN200700755
288 North 1460 West • PO Box 144880 • Salt Lake City, UT 84114-4880 • phone [phone] • fax [phone]
T.D.D. [phone] • www.deq.utah.gov

State of Utah

Department of Environmental Quality

Dianne R. Nielson, Ph.D.
Executive Director

DIVISION OF SOLID AND HAZARDOUS WASTE
Dennis R. Downs
Director

JON M. HUNTSMAN, JR.
Governor

GARY HERBERT
Lieutenant Governor