Aquifer System

Saint-Maurice


Surficial unconfined aquifer on rock or till confined aquifer
The hydrogeological unit is composed of sandy sediments that are divided into two subunits that form aquifers hydraulically isolated from each other: the Saint-Narcisse Moraine and superficial sands. These sediments include sections on semi-confined and confined rock/till aquifer. They are not all found in this hydrogeological unit. The surficial sands include silty marine and deltaic sand, sand and lacustrine silt associated with the Lake Lampsilis and deltaic marine and lacustrine sand of St.Maurice River. Sandy unit overlies fine sediments, forming a thin aquitard. Fluvioglacial or glacial sediments are found under this aquitard. In the valley bottom or on the Laurentian Plateau margin, fluvioglacial sediments can form confined aquifers overlying the bedrock. The surficial deposits are 48-148 m and 24-96 m thick on west and east river bank respectively. The unit is an important recharge area and some others sections are discharges. The hydraulic conductivities are good. Groundwater is good quality, but has high concentration of barium. It also exceeds aesthetic standards for: chloride, sodium, total dissolved solids, hardness, iron, manganese, sulfide and pH.
Unconfined aquifer in rock or till
Located in the northern section of the area, the unconfined aquifer in rock or till is composed of an aquifer formed by network of bedrock fractures. The bedrock is composed of crystalline Precambrian rocks with low fracturing. The rock formations are covered with a till layer of less than 10 m thick. Although this aquifer is under unconfined conditions, this unit isn't generally a good recharge area. Hydraulic conductivities are low. The piezometric surface of watertables included in the bedrock is characterized by strong hydraulic gradients and variable flow directions, corresponding with the slope. The data available on bedrock aquifer do not allow significantly distinguishing aquifers from each other. Unconfined aquifers all show a high storage coefficient in the order of 10^-1. The hydrogeological unit has a moderate vulnerability. The potentially polluting activities are only found in the southern part of the unit. The contamination risk is low. Groundwater has a good quality, but is characterized by high concentrations of iron and manganese. Moreover, there is a problem of hardness.
Surficial unconfined aquifer on rock
The surficial unconfined rock aquifer unit includes glaciofluvial and deltaic/prodeltaic sediments. These are found mainly along streams in the north of the area. These sediments overlie the crystalline Precambrian bedrock, characterized with low fracturing. The deposit thickness commonly varies between 16-48 m with a minimal and maximal thickness of 12 and 96 m respectively. These aquifers have high recharge rates and good hydraulic conductivities. Water percolates and flows in the pores to the streams, draining the valleys. These aquifers are largely exploited despite their restraint size and relative isolation. They are very vulnerable; however the potentially polluting activities are located further south, limiting the risk of contamination. Groundwater is generally good, but it has some problems of fluoride, barium, nitrate and pH. On the aesthetic level, it exceeds the standards for sodium, chloride, total dissolved solids, hardness, iron and manganese.
Semi-confined aquifer on rock or till
The semi-confined aquifer on rock or till hydrogeological unit is composed of an aquifer formed by network of bedrock fractures. It can be divided in two subunits, having different characteristics: the crystalline Precambrian rocks with low fracturing and brittle sedimentary rocks (sandstone and limestone) in the southwestern part of the unit. The rock formations are covered by a thin till unit and an aquitard formed by fine marine deposits. Compared to the confined aquifer unit in the rock/till unit, the semi-confined aquifer has an aquitard of smaller thickness. The common deposits thickness is 4-8 m, but it can reach 24-48 m in some places. The unit isn't generally a good recharge area. The piezometric surface of watertables included in the bedrock is characterized by strong hydraulic gradients and variable flow directions, corresponding with the slope. The data available on bedrock aquifer do not allow significantly distinguishing aquifers from each other. The hydrogeological unit has a moderate vulnerability. The concentration of potentially polluting activities increases the risk of contamination. Groundwater has a good quality, but is characterized by high concentrations of iron and manganese. Moreover, there is a problem of pH.
Surficial unconfined aquifer on semi-captive aquifer on rock or till
The hydrogeological unit is composed of sandy sediments divided into two subunits: the St.Narcisse Moraine and surficial sands. The sediments overlie semi-confined but also confined roc/till aquifer. Thus this hydrogeological unit includes only portions of the subunits. The surficial sands include silty marine and deltaic sand, sand and lacustrine silt associated with the Lake Lampsilis and deltaic marine and lacustrine sand of St.Maurice River. These two subunits forming aquifers hydraulically isolated from each other. These sandy sediments overlie fine marine sediments forming a thin aquitard. Fluvioglacial or glacial sediments are found under this aquitard. In the valley bottom or on the Laurentian Plateau margin, fluvioglacial sediments can form confined aquifers overlying the bedrock. The surficial sediments thickness is generally about 16-48 m. The unit is one of the most important recharge area. It also has good hydraulic conductivities. Water percolates and flows easily through the pores to the stream draining the valleys. The unit is very vulnerable, but the concentration of potentially polluting activities is low, limiting the risk of contamination. Water is good, but has problems of iron, manganese and pH.
Confined aquifer in rock or till
The confined aquifer in rock or till is composed of an aquifer formed by network of bedrock fractures. The bedrock is composed of two subunits: crystalline Precambrian rocks with low fracturing found in the north of the unit and brittle sedimentary rocks (sandstone and limestone). The rock formations are covered with a thin till layer and an thick aquitard formed with fine sediments. Locally, some glaciofluvial, deltaic/prodeltaic and alluvial sediments are found. They may form surficial aquifers. The common sediment thickness is about 48-96 m, but some places show thicknesses of 24-48 m or 96-148 m. This unit isn't generally a good recharge area. Some sectors are discharge areas. Hydraulic conductivities are low. The piezometric surface of watertables included in the bedrock is characterized by strong hydraulic gradients and variable flow directions, corresponding with the slope. The data available on bedrock aquifer do not allow significantly distinguishing aquifers from each other. Confined aquifers all show a low storage coefficient in the order of 10^-4. The hydrogeological unit has a low vulnerability. The potentially polluting activities are concentrated in the cities, which have a higher risk of contamination. Groundwater has a good quality, but is characterized by high concentrations of fluoride, sodium, chloride, iron and manganese. Moreover, there are also problems of dissolved solids and pH.