Artificial recharge of confined prairie aquifer
Date
1993
Authors
Journal Title
Journal ISSN
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Publisher
ORCID
Type
Degree Level
Masters
Abstract
Artificial recharge of a confined aquifer was successfully conducted
through a 30 m deep small diameter well.
The study site selected was located north of Saskatoon, Saskatchewan,
over the Dalmeny aquifer system. Farms and towns in the area
obtain water from wells developed into the aquifer and from
manmade and natural surface water sources. The aquifer covers
an 800 km2 region between the North and South Saskatchewan
rivers.
Treated fresh water was injected into the aquifer formation by
maintaining the water level in the well standpipe above the static
water level of the aquifer. The groundwater quality exceeded 2000 mg/L
total dissolved solids and was aesthetically displeasing to the well
owner because of dissolved iron concentration in excess of 10 mg/L.
The injected water contained less than 0.5 mg/L iron, and less than
1000 mg/L total dissolved solids.
Water injected into the aquifer was subsequently recovered by pumping
the injection well. The recovery efficiency ranged from 44% to 85% of
the theoretical recovery volume, as measured by inorganic chemistry and
electrical conductivity. 15% to 36% of the injected water mixed with
the natural groundwater and its recovery could not be measured by the
adopted methods.
The specific capacity of the aquifer during injection was calculated to
be less than 1 m3 day-1 m-1. The calculated specific capacity of the
aquifer during recovery was estimated to be greater than 4 m3 day-1 m-1
in 1987, but decreased to less than 2 m3 day-1 m-1 at the end of the
field trials.
A preliminary site assessment procedure was established through review
of previous work and the findings of the field program.
The field program was limited because the well was over ten years old
and had begun to show signs of decreased capacity prior to this
research, and because no monitoring wells could be installed in the
study area. Supplementary information relating to artificial recharge
was obtained through laboratory and mathematical models.
Tests conducted using a laboratory scale sand model demonstrated that
density induced flow occurs after fresh water is injected into brackish
water. The fresh water front migrated from a vertical to a horizontal
position over a period of 100 minutes. This observation, applied to
the field site, may partially account for less than 100% recovery
efficiency under artificial recharge.
The fresh water storage in a brackish aquifer was estimated
mathematically as a function of hydraulic gradient, aquifer parameters
and water density. The model indicated density induced flow may
contribute to decreased recovery efficiency of stored fresh water, but
the model capabilities was limited to demonstrating the process, rather
than application and analysis of field data sets.
The net increase of dissolved calcium in the injected water was
calculated to be less than 1 mg/L. The increased calcium
concentrations of the recovered water quality over time was attributed
to the mixing of brackish water with the injected water, not to calcite
dissolution from the aquifer matrix.
Artificial recharge and recovery efficiency of fresh water into a
confined aquifer in Saskatchewan was estimated assuming changes in
water quality due to dispersion. Some additional losses occurred that
may be due to density differences between the injected and original
groundwater, or due to the regional groundwater gradient.
Description
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Citation
Degree
Master of Science (M.Sc.)
Department
Agricultural and Bioresource Engineering
Program
Agricultural and Bioresource Engineering