DERR-2024-005219

Supplemental Geo-Hydrology Information Required for CERCLA Site-Characterization
and Utah DWQ Groundwater Discharge Permit Requirements
Joint EPA-UDEQ, May 2022

To: David Abranovic, ERM Project Coordinator
US Magnesium NPL Site

Rob Hartman, Environmental Manager
US Magnesium

From: Ken Wangerud, Remedial Project Manager
EPA Superfund Remedial Program

Jeff Kolmel, Groundwater Discharge Permit Manager
UDEQ-DWQ/Individual Permitting Program

Date: May 31, 2022

Subj: Completion of the PRI-17 Hydro-geologic CSM for RI-Characterization
of the PRI-15 Area, and Development of a Sitewide Groundwater Monitoring Plan

The purpose of this memo is to inform ERM-USMag of the need (as jointly identified by EPA’s Superfund-
Remedial and the Utah DWQ-Groundwater Discharge Permit programs) for additional site investigations
in the areas of PRI-15 adjoining and to the west of the Facility Operating Area (FOA) and the Retrofit
Waste Pond (RWP) containment project. This work will pertain simultaneously to finalizing PRI-17 RI-
Characterization of the PRI-15 area and development of a groundwater monitoring plan as required by
the Utah Division of Water Quality (UDWQ) Groundwater Discharge Permit (GWDP) to evaluate the
long-term performance of the remedy. It is important to recount the history and basis of this need for
additional information pursuant to CERCLA AOC-for-RIFS Para.34.c, Utah Administrative Code R317-6-
6.15.D, and Section II. I.2 (Compliance Schedule) of the UDWQ GWDP.

Investigations of surface and groundwater were carried out by ERM for PRI-17 (Surface Water
Addendum to Phase 1A Data Report for PRIs 2 & 8-17 (March 2016)1, followed by a more
comprehensive evaluation2 focused mostly on the geohydrology of the ‘Inner PRIs’ (largely within the
RCRA Deferral Area of the recent Settlement Consent Decree). During the 2017-2020 period, USMag
had pursued with UDWQ and EPA the development of the Retrofit Waste Pond (RWP) project (to
include a salt-cap closure) and carried out more intensive design investigations within the planned RWP
area to obtain a GWDP and facilitate an EPA Settlement Consent Decree.

As the containment-control design (which included engineered structural-containment only for the
northern, eastern- and southern perimeter-sides of the RWP) was being advanced by USMag, CERCLA
turned its primary attention to assuring that appropriate RI geohydrology data would be collected to
characterize the lesser-investigated baseline conditions for the groundwater system of the CERCLA-Zone
that adjoin the 1.6 mile-long ‘unbounded’ western side of the RWP and the FOA.

1 Final Old Waste Pond/Current Waste Pond Area Hydrologic Conceptual Site Model, April 2017
2 Phase 2B Hydro Remedial Investigation Data Report (Draft May 2020)
Supplemental Geo-Hydrology Information Required for CERCLA Site-Characterization
and Utah DWQ Groundwater Discharge Permit Requirements
Joint EPA-UDEQ, May 2022

Paragraph 2 of the compliance schedule outlined by UDWQ in the GWDP states that US Mag must
submit a report to UDWQ that fulfills the requirements of Utah Admin. Code R317-6-6.15D for a
Contamination Investigation (currently being addressed through the RI process). The GWDP specifies
that the report must adequately address the groundwater conditions of the RWP as well as the
following items pertinent to the PRI-15/CERCLA-Zone area:
• The extent and severity of existing ground and surface water contamination.
• Evaluation of actual and potential pathways for contaminant migration, both at the surface and
in the subsurface.
• Investigation of the stratigraphy, permeability, ground water flow, and potential contaminant
migration pathways in the future open western side of the subsurface barrier wall.
• Ground water quality upgradient of the US Magnesium facilities.

Paragraph 4 of the Compliance Schedule outlined by UDWQ in the GWDP states that US Mag must
submit a proposed compliance monitoring plan within six months of UDWQ approval of the
contamination investigation (Final RI Report) for use after construction of the vertical hydraulic barrier
wall (VHBW) and RWP. The proposed compliance monitoring plan must evaluate the following lines of
evidence pertinent to the PRI-15/CERCLA-Zone area:
• Monitoring wells must be placed in locations that will evaluate potential subsurface discharge of
wastewater from the RWP, including flow out of the open western side of the RWP and flow
along the pond perimeter, particularly in any zones of higher permeability in the Upper Aquifer
Zone (UAZ), and downward flow through the Deeper Silty Clay Layer unit.
• Placement of wells or other monitoring points must be based on the best available
hydrogeological information obtained in required investigations of this area, and ground water
modeling incorporating this information.

Because additional information is needed by EPA and UDWQ in order to assure the appropriate design
of a compliance monitoring plan, we have outlined the principal study questions (PSQs) and study-area
for which the necessary data-quality objectives (DQOs) can be prepared for joint discussion with our
programs. Our agencies anticipate that the completion and submittal of the Sitewide Hydrology RI
report (to include the results of this undertaking for PRI-17) will necessarily be delayed until this aspect
of investigations is completed.

EPA held scoping meetings in 2017 with USMag/ERM to discuss such investigations, which resulted in:
• USMag agreeing to have its design-contractor for the RWP incorporate cone penetration testing
and hydraulic profiling tool (CPT-HPT) investigations into the 2018-planned drilling investigations
in the western area of the RWP facility (work associated with the State GWDP application); the
CPT encountered equipment difficulties at the outset and USMag immediately abandoned the
planned CPT/HPT work to proceed with sonic-core drilling.
• ERM prepared and submitted a CERCLA Hydro SAP-Mod to install wells to investigate baseline
groundwater conditions in the PRI-15 areas to the north and south of the RWP-VHBW and also
to carry out CPT-HPT investigations of the hydro-stratigraphic conditions along the adjacent PRI-
15 boundary areas.
• Immediately after its CPT-HPT submittal, ERM contacted EPA to instead propose employing
downhole investigations in existing monitoring wells (located within the western area of the
planned RWP) to attempt to utilize nuclear magnetic resonance (NMR) electrical logs and
colloidal borescope flow metering (CBFM) to ascertain stratigraphy and transmissivity
Supplemental Geo-Hydrology Information Required for CERCLA Site-Characterization
and Utah DWQ Groundwater Discharge Permit Requirements
Joint EPA-UDEQ, May 2022

conditions. Because investigations had indicated that the principal groundwater flow conditions
were likely associated with thin (inches) and highly transmissive stratigraphic deposits of oolitic
sands, EPA and UDWQ took the proposal under advisement for further technical discussions
about NMR-CBFM adequacy.
• While developing the NMR-CBFM investigational details, ERM carried out the baseline drilling
and sampling investigations of groundwater conditions, mainly in areas to the north and south
of the planned RWP, and with limited investigation in the PRI15 area to the west (Draft Phase 2B
Hydro RI Data Report, ERM May 2020.
• The agencies approved the NMR-CBFM workplans in phases. The DQOs for the upper aquifer
zone were to (a) determine localized variability of horizontal conductivity and porosity, (b)
define groundwater flux and flow directions, and (c) determine the screened interval that will
adequately monitor migration pathways. These DQOs would be evaluated in the OU-1 RI to
develop a detailed hydrologic conceptual site model.
• NMR logging at 12 locations was done in late-2020, followed by pilot-testing of CBFM in 3 wells
in May 2021. ERM reported the NMR-CBFM investigation results (December 2021)3, noting:
o The NMR instrument recorded continuous electrical-log signal responses that spanned
an approx. 1-meter vertical section of borehole stratigraphy.
o Hydraulic conductivities estimated from the NMR logs ranged from 1-10 ft/day, to 50
ft/day in higher transmissive intervals, to >100-250 ft/day in some UAZ locations.
However, the vertical resolution of the NMR logs did not provide data that correlates
specifically to and indicative of flow conditions within the oolitic sands noted as being
present in geologic drilling logs.
o The CBFM results did not provide sufficiently useful information to further characterize
the stratigraphy and hydrodynamics of the western RWP boundary area.

Superfund and UDWQ staffs have reviewed the NMR-CBFM report of findings and have concluded that
the NMR-CBFM work was unable to fulfill information needs at the appropriate and necessary spatial
resolution. Please find enclosed the principal study questions (PSQs) and study-area for which data
quality objectives (DQOs) for the necessary investigations to be conducted for the PRI-15 area of the
PRI-17 RI and the GWP’s RWP Phase-4 design and monitoring requirements.

It will be important that a Superfund Record of Decision for the CERCLA-Zone includes an appropriate
monitoring system to assure the protectiveness of the unimpacted groundwater resources of PRI-17,
i.e., the areas outside the perimeter of the RWP (upgradient and downgradient), as well as the Lower
Aquifer Zone underlying the RWP. The additional investigations requested by EPA and UDWQ will be
critical in facilitating the design and implementation of a groundwater monitoring system that will be
able to adequately assess the long-term effectiveness of the RWP to contain impacted surface water
and groundwater through the GWDP. The anticipated schedules for UDWQ’s GWP and the ROD process
make it essential that the activities for this EPA-RIFS and GWDP endeavor be completed during 2022-
2023. We look forward to having scoping meeting(s) commence soon.

Attachment: PSQ-DQO

3 Phase 2B RI Nuclear Magnetic Resonance Borescope Data Technical Memorandum, ERM 03 December 20 21
Supplemental Geo-Hydrology Information Required for CERCLA Site-Characterization
and Utah DWQ Groundwater Discharge Permit Requirements
Joint EPA-UDEQ, May 2022

Cc:
Steve Wharton, Chief – Superfund Remedial Unit A
Max Greenblum, EPA Attorney
Dan Hall, DWQ Section Manager - Individual Permitting
Katie Crane, DERR Section Manager – Superfund NPL & Federal Facilities
Michael Storck, DERR Project Manager
Kimberlee Mcewan, Utah Assistant Attorney General
Alan Jones, BLM CERCLA Coordinator