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| Hydrogeology and Hydrogeochemistry | ||||||||
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Oak Ridges Moraine Hydrogeology Study: Overview |
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The Yonge Street Aquifer supplies the Aurora Newmarket Basins with municipal and a variety of other water uses. Present York Region municipal well production in the Yonge Street corridor is approximately 35,000 m3/day and serves a population of about 80,000 people. Detailed estimates of groundwater taking by other aquifer users are not available. Hydraulic head (static level) in the Yonge Street Aquifer has steadily decreased with increasing well field production. "Pump off" drawdowns are now about 40 m below ground surface and "pump off" static levels have decreased to 220 m asl (about the level of Lake Simcoe) compared to pre-production levels of about 260 m asl. Best estimates based on data collected during this study indicate that the well field zone of influence is now approximately 15 km in diameter and 200 km2 in area. The capture zone extends to Ballantrae on the east, King City on the west and Lake Wilcox on the south. The total existing deep aquifer recharge to the capture zone is estimated by this study to be approximately 70,000 m3/day, most of which is derived from the Oak Ridges Moraine kettle lake and riparian margin of the capture zone. Increased pumping locations and rates may be expected to further drawdown the static levels and extend the zone of capture in all directions including southerly beyond the the kettle lake zone of the Moraine. Further aquifer static level drawdown and expansion of the capture zone, however, may result in adverse interference with esisting deep aquifer users especially those to the north of Newmarket. Additional deep aquifer monitors are required. Other than the decrease in the static levels (hydraulic head) and the movement towards and the mixing of upper Moraine aquifer waters with deep channel aquifer residual waters, no measurable impact of pumping of the Yonge Street Aquifer has been observed. Stream flow records in the East Holland and East Humber rivers and elsewhere do not demonstrate any base flow influences. This study suggests that static level drawdowns in the upper Moraine aquifers may induce increased snowmelt and stormwater recharge in the Central Moraine Recharge Area and therefore local headwater stream baseflow is not measurably affected, i.e., flood flows and evapotranspiration losses are reduced.
These figures illustrate the deep (below 200 m asl) Yonge St. Aquifer capture
zone for the Aurora Basin. The capture zone delineation is interpreted from
the static level contours prepared from post 1980 water and test well records
for water found/screen depth below 200 m asl.
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| © 2001, Hunter GIS |