When you erect your silt fencing and place the sandbags for erosion control at the beginning of construction, you need to have the city inspector (from the engineering or sewer department probably) look at it. Remember to put these in place as firmly as possible as during the construction these will come of and when it does it might cause dirt escape from the jobsite. Remember that when this happens, the city inspector has a right to close down your job or in some extreme cases, I even heard that the project manager of the jobsite ended up in jail due to dirt from the site entering into the city sewer system.