Anything that is soluble in the water can travel with the water, so you're talking about any kind of dissolved inorganic salts, sodium chloride, iron, aluminum, or anything that will stay in the water. That also includes organic compounds like the naphthenic acids, which are soluble. So anything that can flow with water can potentially end up in groundwater. As long as it's soluble in the water, it will stay with the water.
As Ms. Griffiths also alluded, when these waters mix in the ground with different chemistries, reactions can occur. So at that point, some things may fall out of the water and stay in the reservoir. As long as it's soluble in the water, it will go where the water goes.