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The high terraces sands on deltaic sands and gravels are overlying Precambrian bedrock and sedimentary platform. The Precambrian bedrock is massive and little fractured, showing unproductive aquifer. Sedimentary formations are highly fractured and shales are very brittle, demonstrating good potential aquifer. These units are covered by marine silts and clays of the Champlain Sea followed by deltaic sands and gravels and finally a thin alluvium layer. These sediments represent the hydrogeological unit called high terraces sands on deltaic sands and gravels. This unit are partly located in the discharge areas, along rivers Saint-Anne and Jacques Cartier, mainly in the northeast section of Portneuf area. The predominant hydraulic connection between aquifer and rivers is indirect, showing that groundwater seeps along the river banks and that the river bed overlies a silt and clay unit or the bedrock. On the Jacques Cartier River, some sections of the river bed overlie sedimentary rocks or sands and gravels, suggesting connection between the two aquifers. The connection is the discharge area. The high terraces sands on deltaic sands and gravels have one of the best aquifer potential. The water table is under unconfined conditions, thus the aquifer is vulnerable to surface contamination. Groundwater types are sodium bicarbonate and calcium chloride and shows low mineralization. |
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Physiography
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| Hydrogeological region | St. Lawrence Platform |
| Hydrogeological context | |
| Relief | The hydrogeological unit is located under and along Sainte-Anne and Jacques Cartier River. Essentially present in the northwest of the area, the high terraces sand on deltaic sands and gravels are located on medium altitudes between the sedimentary platform and the rugged relief. Those sediments are found on gentle slope, descending from north to south. |
| Area | 93.00 km2 |
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Lithology
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| Description | The rock formations underlying the high terraces sand on deltaic sands and gravels belong to the Precambrian bedrock or sedimentary formations. The sections of the Precambrian bedrock considered are mainly composed of gneiss and gabbro. The granodiorite gneiss is the dominant unit. Sedimentary formations include limestones of the Trenton Group and shales of the Utica Group. The rock formations are covered by marine silts and clays of the Champlain Sea followed by deltaic sands and gravels and finally the high terraces sands. |
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Aquifer
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| Aquifers | List of aquifers
high terraces sands on deltaic sands and gravels surficial aquifer
igneous rock aquifer |
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