1
25-037
Geochemical Characterization to Support Groundwater Remedy
Selection at a Former Uranium Mill Site
Keaton Belli
Geosyntec Consultants, Oakland, CA, USA
Chelsea Bokman
Geosyntec Consultants, Oakland, CA, USA
Jennifer Nyman
Geosyntec Consultants, Oakland, CA, USA
Liz Moran
Department of Energy Office of Environmental
Management, Moab, UT, USA
Ken Pill
North Wind Portage, Grand Junction, CO, USA
INTRODUCTION
The Moab Uranium Mill Tailings Remedial Action
(UMTRA) Project Site (Site) is a former uranium-ore pro-
cessing facility near Moab, Utah, where production ended
in 1984. The United States Department of Energy Office of
Environmental Management (DOE-EM) is responsible for
remediating the site to meet 40 Code of Federal Regulations
(CFR) 192 standards promulgated by the United States
Environmental Protection Agency under the authority of
the Nuclear Regulatory Commission (NRC). Tailings from
the former mill were stored in an unlined impoundment
(tailings pile), totaling 16 million tons of waste material.
Surface cleanup has been ongoing since 2009 and consists
of removal and transport of tailings via rail to an off-site
disposal facility in Crescent Junction, Utah, with an esti-
mated completion date around 2029.
Gravity-driven migration of tailings fluids and recharge
through the tailings pile and former on-site ore storage
areas in the northeastern part of the site led to contamina-
tion of site soil and groundwater. The primary contaminant
of concern is ammonia, which was present in fluids used
in the milling process (DOE 2003). Uranium is a con-
taminant of potential concern. An interim groundwater
remedy is currently in place that utilizes a system of extrac-
tion and injection wells to limit discharge of contaminated
groundwater into the nearby Colorado River. Exceedance
of surface water standards for ammonia are a principal con-
cern due to potential endangered species fish habitat areas
along the Colorado River adjacent to the Site. When neces-
sary, surface water diversion is used to lower surface water
ammonia concentrations when suitable habitats develop
for endangered young-of-year fish.
Once surface cleanup concludes and the tailings pile is
removed, a formal groundwater remedy must be selected
and documented in a Groundwater Compliance Action
Plan (GCAP). Under Title 1 of the Uranium Mill Tailings
Radiation Control Act, natural flushing (i.e., monitored
natural attenuation), may be selected as the ground-
water remedy if it can be demonstrated that the remedy
will achieve groundwater standards within 100 years. The
40 CFR 192 groundwater standard for uranium is 44
micrograms per liter (µg/L), and the target groundwater
concentration of ammonia based on adverse effects on
local fish species is 3 milligrams per liter (mg/L). A col-
laboration with Geosyntec Consultants, Inc. (Geosyntec),
the Moab UMTRA Project team, the DOE Office of
Legacy Management, the DOE-EM, and the Network of
National Laboratories for Environmental Management and
Stewardship was held in 2022 with the goal to generate
actionable recommendations to develop a GCAP for the
Site. The primary recommendation was development of a
groundwater fate and transport model to predict the reme-
dial timeframe under various groundwater remedies. This
paper presents the results of soil and groundwater sampling,
geochemical modelling, and laboratory column and batch
reactor testing that will be used to parameterize a numerical
model for estimating the remedial timeframe under various
scenarios, including natural flushing.
SOIL AND GROUNDWATER
COLLECTION
Soil and groundwater samples were collected from six
temporary boreholes that were advanced using a track-
mounted sonic rig. Borehole locations were identified
25-037
Geochemical Characterization to Support Groundwater Remedy
Selection at a Former Uranium Mill Site
Keaton Belli
Geosyntec Consultants, Oakland, CA, USA
Chelsea Bokman
Geosyntec Consultants, Oakland, CA, USA
Jennifer Nyman
Geosyntec Consultants, Oakland, CA, USA
Liz Moran
Department of Energy Office of Environmental
Management, Moab, UT, USA
Ken Pill
North Wind Portage, Grand Junction, CO, USA
INTRODUCTION
The Moab Uranium Mill Tailings Remedial Action
(UMTRA) Project Site (Site) is a former uranium-ore pro-
cessing facility near Moab, Utah, where production ended
in 1984. The United States Department of Energy Office of
Environmental Management (DOE-EM) is responsible for
remediating the site to meet 40 Code of Federal Regulations
(CFR) 192 standards promulgated by the United States
Environmental Protection Agency under the authority of
the Nuclear Regulatory Commission (NRC). Tailings from
the former mill were stored in an unlined impoundment
(tailings pile), totaling 16 million tons of waste material.
Surface cleanup has been ongoing since 2009 and consists
of removal and transport of tailings via rail to an off-site
disposal facility in Crescent Junction, Utah, with an esti-
mated completion date around 2029.
Gravity-driven migration of tailings fluids and recharge
through the tailings pile and former on-site ore storage
areas in the northeastern part of the site led to contamina-
tion of site soil and groundwater. The primary contaminant
of concern is ammonia, which was present in fluids used
in the milling process (DOE 2003). Uranium is a con-
taminant of potential concern. An interim groundwater
remedy is currently in place that utilizes a system of extrac-
tion and injection wells to limit discharge of contaminated
groundwater into the nearby Colorado River. Exceedance
of surface water standards for ammonia are a principal con-
cern due to potential endangered species fish habitat areas
along the Colorado River adjacent to the Site. When neces-
sary, surface water diversion is used to lower surface water
ammonia concentrations when suitable habitats develop
for endangered young-of-year fish.
Once surface cleanup concludes and the tailings pile is
removed, a formal groundwater remedy must be selected
and documented in a Groundwater Compliance Action
Plan (GCAP). Under Title 1 of the Uranium Mill Tailings
Radiation Control Act, natural flushing (i.e., monitored
natural attenuation), may be selected as the ground-
water remedy if it can be demonstrated that the remedy
will achieve groundwater standards within 100 years. The
40 CFR 192 groundwater standard for uranium is 44
micrograms per liter (µg/L), and the target groundwater
concentration of ammonia based on adverse effects on
local fish species is 3 milligrams per liter (mg/L). A col-
laboration with Geosyntec Consultants, Inc. (Geosyntec),
the Moab UMTRA Project team, the DOE Office of
Legacy Management, the DOE-EM, and the Network of
National Laboratories for Environmental Management and
Stewardship was held in 2022 with the goal to generate
actionable recommendations to develop a GCAP for the
Site. The primary recommendation was development of a
groundwater fate and transport model to predict the reme-
dial timeframe under various groundwater remedies. This
paper presents the results of soil and groundwater sampling,
geochemical modelling, and laboratory column and batch
reactor testing that will be used to parameterize a numerical
model for estimating the remedial timeframe under various
scenarios, including natural flushing.
SOIL AND GROUNDWATER
COLLECTION
Soil and groundwater samples were collected from six
temporary boreholes that were advanced using a track-
mounted sonic rig. Borehole locations were identified