Abstracts

POSTER SESSION: Innovation in the
Remediation of Contaminated Sites
Thursday October 29, 16:40
Room: Regent
321 - Application of Push-Pull Tests to Define Biogeochemical
Controls on Selenium and Nitrate Attenuation in Saturated Coal
Waste Rock
Marcie Schabert, M. Jim Hendry, & S. Lee Barbour
Department of Geological Sciences – University of Saskatchewan, Saskatoon, Saskatchewan,
Canada
Surface mining of steelmaking coal in the Elk Valley, British Columbia, Canada, has resulted
in the release of constituents of interest such as selenium (Se) and nitrate (NO 3-
) into
the Elk River. Oxidation of sulfide minerals in the unsaturated coal waste rock generates
water-soluble forms of Se (selenite (SeO 3
2–
) and selenate (SeO 4
2-
) that are mobile in the
aqueous phase. Nitrate, introduced to the waste rock through the blasting process, is also
water soluble and mobile in the aqueous phase. Limited data suggests that the attenuation
of Se and NO 3
via reduction can occur in saturated waste rock, therefore the placement of
waste rock in topographic low areas, such as backfilled pits, could create saturated conditions
in which Se and NO 3-
attenuation would be enhanced. A push-pull test is an in situ
method that can be used to examine physical, chemical, and biological characteristics of an
aquifer. Testing involves injecting water spiked with conservative and reactive tracers into
the formation, allowing the spiked water to react within the formation for a period of time,
and then extracting it. Dilution of the injected water can be quantified by monitoring the
concentration of the conservative tracers during extraction. Any loss of reactive tracer beyond
that due to dilution can be attributed to physical-chemical reactions in the formation.
In this study, push-pull tests were used to determine if SeO 4
2–
and/or NO 3-
can be attenuated
within saturated waste rock. Chloride (Cl - ) and deuterium in the water molecules
(δ 2 H) were used as conservative tracers, and either dissolved oxygen (O 2
), SeO 4
2–
, NO 3-
,
or both SeO 4
2–
and NO 3-
were used as reactive tracers. The injection volume for these
tests was between 910 to 1005 L of spiked water, and the reaction time ranged between
19 and 67 hours (h). Extraction was conducted for 8 h, with samples for geochemical
analysis being collected on either 15 or 30 min intervals. In addition to geochemical samples,
pH, temperature, and reduction potential were monitored during both the injection
and extraction phases. Concentrations of tracers were normalized relative to the injection
concentration of each tracer. Normalized plots of reactive tracers were compared to those
of conservative tracers for each test to determine if O 2
, SeO 4
2–
, and NO 3
reduction is occurring
in the saturated waste rock at the scale of the testing.
164 IAH-CNC 2015 WATERLOO CONFERENCE