Critical/Class 3 600mm surface water sewer

[Mattg4321]

After applying to local WA via BC for approval, it turns out they refused the application because we have a 600mm rainwater sewer that starts in our garden. Plan attached although it’s incorrect as it’s not as close to the house as shown. 
 

After a bit if investigation and various shrubs etc cut back and digging we’ve found the manhole under 4 inches of dirt. It’s the point where 225mm joins 600mm class 3/critical sewer. Then heads off away from the plot. 225mm sewer is currently down the side of the house around 600mm from house. 
 

It’s 2.5m away from the corner of proposed extension, but WA want 3.5m as it’s a ‘critical sewer’ Foundations to be over 1m below invert level and manhole to be accessible. 
 

We’ve requested a site visit. Hopefully common sense will be applied. Has anyone had similar?