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Part of your decision will depend on where the water is going to be disposed of. Going straight into a surface water stream will need higher levels of wastewater treatment than running over a vegetated surface or a shallow soak away.
You should only need the final flush of wash water for the borehole to be super chlorinated. There should still be a residual of free chlorine when the water is finally flushed out. However the initial dose should not be excessive as that would be a waste of the chemical. Chlorine is highly reactive and it will be used up once it mixes with water with organic matter in.
If you can store the wash water for a while and test it before draining it to the environment, you can ensure the chlorine has all been reacted. If the water still has free chlorine mix it with some soil and test again.
The turbidity can also be dealt with by storing the wash water for an hour or two until it looks clear. Running it through some grass will help remove any other traces of solids before discharge to the environment.