Plans and profiles of proposed improvements and utility layouts, including sewers, storm drains and water lines, and feasible connections to gas, telephone and electrical utility systems. The plans and profiles of water and sewer layouts, whether on-site, off-site or off-tract, shall show size and type of pipes and mains, slope, pumping stations, fire hydrants, standard details and trench repair details for street crossings. All utilities shall be installed underground. If private utilities are proposed, they shall comply fully with all Township, county, state and federal regulations. If service will be provided by an existing utility company, in lieu of detailed plans, a letter from that company stating that service will be available before occupancy will be sufficient.