Characterization of general and singular features of major aquifer systems in the Saguenay-Lac-Saint-Jean region

Figures & data

Figure 1. Location of the Saguenay-Lac-Saint-Jean region and its principal physiographic features. The delineation of the study area is based on municipal boundaries.

Figure 2. Schematic block diagram of aquifer types identified in the Saguenay-Lac-Saint-Jean region (CERM-PACES 2013).

Figure 3. Bedrock geology of the Saguenay-Lac-Saint-Jean region, showing important structural features (brittle and ductile main structures), as the major faults delimiting the graben and the local uplands within the graben.

Figure 4. Compiled and calculated transmissivity in the fractured rock aquifers (adapted from CERM-PACES 2013).

Figure 5. (a) Position of the 134 cross sections developed by interpreting local stratigraphic logs from boreholes and soundings. (b) An example of cross section: (A) cross section location; (B) cross-section interpretation (Modified from Chesnaux et al. 2017).

Figure 6. Compiled and calculated transmissivity in the granular aquifers (adapted from CERM-PACES 2013). Main granular aquifers in the Saguenay-Lac-Saint-Jean region, forming either free-surface aquifers, shown in yellow and orange, or confined aquifers, indicated by hatching.

Figure 7. Generalized cross section showing the different salinization pathways occurring in the Saguenay-Lac-Saint-Jean region. Bedrock groundwater evolves from Ca,Na-HCO₃ in unconfined environments to Ca,Na-Cl in rock-dominated environments due to interactions with basement fluids (water-rock interactions) along the graben fault system (groundwater flow line). The groundwater in the granular aquifers evolves from the recharge groundwater (Ca-HCO₃) by Ca²⁺_water-Na⁺_mineral ion exchange process in a confined environment (Na-HCO₃) and through possible mixing with the Laflamme seawater end-member (Na-Cl). This latter evolution might also be observed in bedrock aquifers where confining conditions prevail (Modified from Walter et al. 2017).

Figure 8. Relative proportion of the major cations (calcium and sodium) in the collected groundwater in (a) the bedrock aquifers, and (b) the granular aquifers.

Table 1. Number of groundwater samples by aquifer type and water type.

Aquifer type	Water type	No. of samples
Fractured bedrock	(Na-Ca)-HCO3	127
Fractured bedrock	(Na-Ca)-Cl	26
Quaternary granular	(Na-Ca)-HCO3	144
Quaternary granular	(Na-Ca)-Cl	19

Table 2. Descriptive statistics for groundwater chemistry.

Parameters	Detection limit (mg/L)	N	Min.	Q1 – 25%	Median	Q3 – 75%	Max.
pH*	-	316	4.4	6.5	7.6	8.1	10.1
Temperature (°C)*	-	316	1.7	6.9	7.5	8.6	17.5
Dissolved oxygen (mg/L)*	-	316	0	0	1.1	4.5	43.7
Redox potential (mV)*	-	316	-156	-31.5	70.5	101	195.2
Conductivity (uS/cm)	-	316	4	134	278	470	10,140
Bicarbonates*****	1	316	2	52.25	110	170	620
Silicium**	0.1	316	0.1	4.8	5.6	7.1	16
Sodium**	0.1	315	0.89	3.25	11	45.5	1,800
Calcium**	0.1	314	0.12	9.5	23	50	1,500
Potassium**	0.1	313	0.12	0.96	1.8	3.6	55
Chloride***	0.05	312	0.14	1.87	8.7	36.25	4,200
Magnesium**	0.01	312	0.02	1.47	3.85	8.13	140
Strontium**	0.002	312	0.003	0.06	0.18	0.5	37
Sulfates***	0.5	311	0.2	4.5	10	17	420
Barium**		298	0.0025	0.0163	0.0395	0.0898	1.2
Aluminium**	0.001	285	0.001	0.004	0.007	0.016	0.23
Manganese**	0.0004	277	0.0004	0.0029	0.014	0.053	2.4
Zinc**	0.005	262	0.0016	0.0082	0.015	0.03	0.71
Ammonium****	0.02	252	0.02	0.04	0.07	0.21	3
Boron**	0.005	234	0.005	0.011	0.032	0.1	0.75
Lead**	0.0001	225	0.0001	0.0002	0.0003	0.0006	0.0073
Fluoride****	0.1	222	0.1	0.2	0.6	1.5	4.9
Copper**	0.0005	220	0.0005	0.0016	0.0045	0.013	0.35
Molybdenum**	0.0005	189	0.0005	0.001	0.0018	0.0031	0.024
Nitrate***	0.1	154	0.02	0.1	0.3	1.08	8.6
Iron**	0.1	142	0.03	0.06	0.13	0.38	18
Silver**	0.0001	95	0.0001	0.0001	0.0002	0.0003	0.009
Nickel**	0.001	78	0.001	0.001	0.001	0.003	0.02
Uranium**	0.001	66	0.001	0.001	0.002	0.003	0.02
Chromium**	0.0005	48	0.0005	0.0007	0.001	0.0016	0.011
Bromide***	0.1	42	0.1	0.4	1.5	6.1	45
Lithium**	0.01	35	0.01	0.01	0.01	0.02	0.57
Inorganic phosphorus****	0.03	22	0.04	0.05	0.07	0.1	0.5
Vanadium**	0.002	22	0.002	0.002	0.003	0.003	0.012
Cobalt**	0.0005	17	0.0006	0.001	0.0013	0.0025	0.0066
Sulfur (mg/L)	0.02	15	0.02	0.05	0.16	0.55	16
Cadmium**	0.0002	9	0.0002	0.0003	0.0003	0.0007	0.0007
Antimony**	0.001	9	0.001	0.001	0.001	0.002	0.005
Tin**	0.001	4	0.001	0.001	0.001	0.002	0.003
Titanium**	0.001	3	0.001	0.001	0.001	0.002	0.004
Beryllium**	0.0005	2	0.0008	0.0017	0.0026	0.0035	0.0044
Bismuth**	0.00025	1	0.0007	0.0007	0.0007	0.0007	0.0007
Selenium**	0.001	1	0.001	0.001	0.001	0.001	0.001

Analytical methods:

* multiparameter probe (in situ);

** inductively coupled plasma mass spectrometry;

*** Ionic chromatography;

**** Specific probe;

***** Titration;

25 and 75 header = the first and the third quantiles.

TDS is calculated using the software Aquachem v.5.0.

CERM-PACES. 2013. Résultats du programme d’acquisition de connaissances sur les eaux souterraines de la région Saguenay-Lac-Saint-Jean. Chicoutimi: Centre d’études sur les ressources minérales, Université du Québec à Chicoutimi, 308 pp.

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Chesnaux, R., M. Lambert, J. Walter, V. Dugrain, A. Rouleau, and R. Daigneault. 2017. A simplified geographical information system (GIS)-based methodology for modeling the topography of bedrock: Illustration using the Canadian Shield. Journal of Applied Geomatics 9 (1): 61–78. doi:10.1007/s12518-017-0183-1.

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Walter, J., R. Chesnaux, V. Cloutier, and D. Gaboury. 2017. The influence of water/rock − water/clay interactions and mixing in the salinization processes of groundwater. Journal of Hydrology: Regional Studies 13 (2017): 168–188.

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