I'm working on a mixed-use tower construction project in Morocco. 

The site being near a pretty big river that crosses the city, coming from the ocean nearby, the contractor wants to pump excess rainwater into the river.

- This rainwater has been naturally running through drainage canals around the construction site, which makes it free of sediments and contaminants from construction activity.

- All contaminated water from oil, gasoline and other stuff goes through a Hydrocarbon separator, and the water coming out of the separator is directly rejected into the stormwater drainage canals around the construction site.

My questions are : 

- Can the contractor release the drained stormwater into the river ?

- What are the best practices for dealing with excavated dirt that has been mixed with concrete ?

Thank you