Heavily contaminated sediment must be land-disposed. The discharge into open water impacts the quality of the water, the quality of the receiving sediments and the fauna. The particles are suspended during rejection. Land disposal can cause contamination of the water system (groundwater runoff, wells and water intakes) and induces occupation of the territory. Compared to management in open water discharge, the disposal management costs can be two to five times higher for good quality sediments, and up to seven times higher for slightly contaminated sediments. The accurate characterization of sediments is therefore essential in order to determine the best management method. The reactivity of the sediments due to the change in physicochemical conditions must be considered. When the sediments are dredged from the lake, the geochemical conditions are modified. The sediments are desaturated by evaporation and gravity flow. The sediments become exposed to oxidizing agents such as oxygen and water. The reduced phases such as pyrite can then undergo direct or indirect oxidation and thus result in the release of associated metals. The direct oxidation formula of pyrite is as follows in Equation (1) [23]:  
\[2\text{FeS}_{2}+7\text{O}_{2}+2\text{H}_{2}\text{O}\to 2\text{Fe}^{2+}+4 \text{SO}_{4}{}^{2-}+4\text{H}^{+} \tag{1}\]Many intermediates are actually formed, including, for example, native sulfur (S0), sulfites (SO3\({}^{2-}\)) or thiosalts, which are partially oxidized compounds that are metastable under aqueous conditions and conditions wherein acid generators are delayed. Taking into account the oxidation of Fe(II) to Fe(III) and the precipitation of Fe(III), the overall reaction of the direct oxidation of pyrite can be written as in Equation (2):  
\[\text{FeS}_{2}+15/4\text{Fe}^{3+}+7/2\text{H}_{2}\text{O}\rightarrow\text{Fe( OH)}_{3}+2\text{H}_{2}\text{SO}_{4} \tag{2}\]  
The indirect oxidation of pyrite occurs when the pH is sufficiently low (pH \(<\) 3), whereat Fe (III) becomes the main electron acceptor of the reaction (Equation (3)):  
\[\text{FeS}_{2}+14\text{Fe}^{3+}+8\text{H}_{2}\text{O}\rightarrow 15\text{Fe}^{2 +}+2\text{SO}_{4}{}^{2-}+16\text{H}^{+} \tag{3}\]  
Similarly, the acid generation is then accelerated. The oxidation of chalcopyrite is as follows (Equations (4) and (5)):  
\[\text{CuFeS}_{2}+4\text{O}_{2}\rightarrow\text{Cu}^{2+}+2\text{SO}_{4}{}^{2-} +\text{Fe}^{2+} \tag{4}\]  
\[\text{CuFeS}_{2}+16\text{Fe}^{3+}+8\text{H}_{2}\text{O}\rightarrow 17\text{Fe}^{2 +}+\text{Cu}^{2+}+2\text{SO}_{4}{}^{2-}+16\text{H}^{+} \tag{5}\]  
The acidity produced by sulfide oxidation can be neutralized if carbonates are present (behaving like pH buffers). The neutralization reaction can be written as follows in Equation (6):  
\[\text{MCO}_{3}+\text{H}^{+}\rightarrow\text{M}^{2+}+\text{HCO}_{3}{}^{-} \tag{6}\]  
Organic compounds are soluble and mobile and their effects on the complexation of metal elements will promote the sorption of the metals during sediment dredging [24]. Soil organic matter forms complexes with metals by ion exchange, surface adsorption, or chelation [25]. However, the release of organic matter is influenced by pH variation. Metals bound to dissolved organic matter can be found in solutions [26]. This study was undertaken with the following objectives: (i) to determine the extent and levels of the contamination of the sediments of Lake Osisko by physical, chemical and mineralogical characterization; (ii) to perform a first evaluation of the quality of the water and sediments; (iii) to carry out leaching tests mimicking the exposure of dredged sediments to oxidizing agents in order to quantify the sediments' reactivity.