On sites with lots of existing underground utilities where you will do excavation, in some cases it might be best practice to do vacuum excavation, depending on the soil type and the frequency of the utilities you will encounter. In some cases the soil may need to be loosened first, with a number of different methods from hand digging to using water jets. Use of vacuum excavation method greatly reduces the chance of utility strikes. This method is also called suction excavation.
this method does not work on clay type soils well unless it is really dry