I will try to help.
Listen my friend.
The first sentence "The Contractor shall be responsible for the design.."
is not passive voice.It's just a simple sentence with a modal.
how did I know that these sentence is not passive voice ?
1- "shall " ,similar to "will", is a modal . And it ,often with the pronouns' I' and 'we',is used to indicate future action.
2- the modals in passive voice follow this structure :
subjet+modal+be verb (in the appropriate tense)+past participle
In your sentence we have subjet(the contractor)+modal(shall)+be+But here we need past participle of the verb and " responsible" is not a past participle ,it 's not even a verb.
* This is an example for a modal in the passive voice :
All library books must(should/may/might/..) be returned to the library
before July 1st.
For the second sentence "The Contractor shall design and implement..).It's also a sipmle sentence to indicate a future action.Why ? becasu of the using of the modal "shall".
If you want to use passive voice, the sentence should be :
A flow diversion shall be designed and implemented by the constractore to ensure..
I hope that I was helpful...
Remember I could be easily wrong, so that you should wait for the other members to reply on you..I'm just a beginner trying to help as mutch as I can
Take care ........