DSHW-2018-003324 - 0901a068807ec7d4

April 12, 2018
8200-FY18-015
Div of Waste Management
and Radiation Control
APR 1 2 2O18
Orbital ATK
p s RN- 2o la -00332-f-
Mr. Scott T. Anderson, Director
Utah Department of Environmental Quality
Division of Waste Management and Radiation Control
195 North 1950 West
P.O. Box 144880
Salt Lake City, Utah 84114-4880
Re: ATK Launch Systems Inc., Response to UDWMRC Comments on Proposed
Groundwater Exposure Units, Promontory EPA ID #UTD009081357
Dear Mr. Anderson:
In a March 1, 2018 letter your office provided comments on the ATK Launch Systems
Promontory (ATK) proposal identifying exposure units and associated wells to be used in
the Human Health and Ecological Risk Assessments. Included with this letter is the
response to those comments provided by Geosyntec.
The UDWMRC comments recommended a revision to the exposure units proposal.
However, in the response it is explained that a revision is not necessary as the requested
additional information will be provided in a subsequent work plan. Therefore, the
proposal remains the same as originally submitted.
If you have questions regarding this report, please contact Paul Hancock at (435) 863-
3344.
Kris H. Blauer
Manager, Environmental Services
ATK Launch Systems, Inc.
Orbital ATK, Inc. • P.O. Box 707, Brigham City, Utah 84302 • 435-863-3511
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RESPONSE TO COMMENTS
Proposed Groundwater Exposure Units
Orbital ATK
Promontory Facility
Brigham City, UT
Prepared by
Geosyntec Consultants, Inc.
1376 Miners Dr. Suite 108
Lafayette, CO 80026
Project Number DE0188
March 2018
Plume Delineation - Response to Comments
Orbital ATK Promontory
Orbital ATK's Response to the Division of Waste Management and Radiation Control
Comments:
Proposed Groundwater Exposure Units for Human Health and Ecological Risk
Assessments— Promontory Facility
Comments:
1. General Comment: ATK has previously agreed to evaluate each exposure unit for both a
"maximum risk" based on the highest concentrations of COPCs detected and the risk
associated with a 95% UCL for the wells identified. If this will not be done for any of the
plumes (or exposure units) besides the springs, please provide an explanation to support the
decision not to do this.
Response to Comment 1: The main intent of the memorandum was to evaluate each of the
groundwater wells for inclusion or exclusion in the HHRA, designate specific wells as
background, and assign wells selected for inclusion to an exposure unit. This task was
performed using trichloroethene (TCE) and perchlorate data to guide the process, because
these two compounds are considered key analytes for this site and will likely be risk drivers.
The details of the HHRA process will be presented in a brief work plan which will address all
of the comments contained in this document. However, for clarification, the HHRA process
will include a quantitative evaluation of risk using both the highest concentrations of COPCs
and the 95% UCL, as was discussed in the August 2017 meeting with UDWMRC.
2. Plume #1: As discussed previously, and noted in the Geosyntec Memorandum dated August
9, 2017, the hexavalent chromium plume that has been detected in the M-508 area should be
evaluated quantitatively in the risk assessments. Please revise the document to address how
this will be done.
Response to Comment 2: As noted in the response to Comment #1, TCE and perchlorate data
were used to guide the plume delineation process. Hexavalent chromium, and other COPCs will
be evaluated quantitatively in the M-508 area. This process will be presented in the HHRA work
plan. The plume delineation memo was not intended to exclude hexavalent chromium, instead it
focused on TCE and perchlorate for plume delineation, as discussed above.
3. Plume #4: RDX is included on the list of Groundwater Protection Standard Constituents in
the Post-Closure Permit and has been detected in this plume at concentrations exceeding the
EPA tap water screening level. Please revise the memorandum to address how RDX will be
evaluated in the risk assessments.
Response to Comment 3: The process for screening COPCs, including RDX will be presented
in the HHRA work plan. All available RDX data, including the latest data collected from
additional wells in the fall of 2017, will be screened against the appropriate screening level to
determine the plumes where RDX will be carried forward as a COC. The plume delineation
Response to DWMRC Comments on Plume delineation memo.docx Page 1
Plume Delineation - Response to Comments
Orbital ATK Promontory
memo was not intended to exclude RDX, instead it focused on TCE and perchlorate for plume
delineation, as discussed above.
Response to DWMRC Comments on Plume delineation memo.docx Page 2