Geotechnical News March 2011
55
WASTE GEOTECHNICS
initially installed data loggers (see
below).
Data Logger Installation
Details
In Spring 2006, Nests 3 and 4 were
each instrumented with four grouted
LTC (level, temperature, conductivity)
Solinst 3001 data loggers to permit
real-time monitoring of contaminant
migration. Loggers were installed
in the upper and lower regions of
both the clay till and the saturated
portion of the Wood Creek Sand
Channel. Monitoring wells were not
initially constructed here, given the
likelihood of their damage during
dyke construction. This precaution
was shown to be well-founded:
several of the Nest 2 monitoring well
casings have been bent due to dyke
shifts during its construction. This has
complicated extending pre-existing
well casings and in extreme cases,
wells can no longer be sampled.
Once dyke construction is completed,
sacrificed loggers will be replaced with
monitoring well nests similar to Nests
1 and 2 (Nest 3, 2010; Nest 4, 2011).
Infiltration Pond
Another key component to the
research infrastructure is a field-scale
analogue of the STP - the Infiltration
Pond (completed August 2008). The
Infiltration Pond (Figure 3) permits
field-scale investigation of the rate of
infiltration of PAwater into the clay till,
and of the microbial and geochemical
impact of this water as it migrates
through the sediments.
Infiltration Pond Construction
Details
During excavation, vegetation, muskeg
and a locally present surficial sand
layer were stripped away and the
pond floor was excavated to a depth
of 1.3m into the clay till unit (Figure
3). The pond top was aligned below
the base of the surficial sand layer to
prevent lateral leakage of PA water
through a highly conductive stratum
into the surroundings. Excavated
clayey material was deposited around
the perimeter of the excavation and
compacted with a backhoe to replace
the removed organic and sand layers
and to line the sidewalls with a low
permeable material. To provide
locations for sampling the till beneath
the pond over time, and to enable
collection of water samples from just
above the point of infiltration, thirty
slotted PVC pipes were evenly spaced
within the pond and embedded 0.15m
into the till. Tailings sand was deposited
(1m thickness) and compacted around
the pipes to set them in place. Lastly, a
water truck was used to flood the pond
with PA water to ~0.2 m above the top
of the tailings sand. Four continuous
core samples were collected to a depth
of 12m during pond construction to
characterize the sediments and pore
waters prior to infiltration. Future
samples will be taken by coring
beneath the slotted pipes in 2010 and
2011, to quantify both the progress of
infiltration by isotope tracking, and the
microbially-mediated and geochemical
impact of PAwater ingress into the clay
till.
In Situ Aquifer Test Facility
The In Situ Aquifer Test Facility is a
system of injection and monitoring
wells, positionedwithin theWoodCreek
Sand Channel, created as a predictive
field-scale model. Two injection/
monitoring wells were constructed
in Spring 2007: one screened within
yellowish-red sand (STP-07-158-
SS), the other deeper, within grey
Figure 3. Cross-section schematic of the Infiltration Pond. The pond is square in
shape, excavated ~1.3m deep into competent clay till. Thirty 10cm I.D. slotted
PVC casing pipes were placed across its base to facilitate collection of future sedi-
ment and water samples. Pipes were recessed only deep enough to fix the screens
in place, and covered with Nilex Nonwoven 4545 geotextile filter socks.
