Modern day landfills are designed and constructed with environmental protection systems. A liner system creates an impenetrable barrier between soil and groundwater and what goes into the landfill. A typical liner starts with a composite liner of clay and synthetic material. Clay is compacted to increase impermeability (meaning that liquids can’t get through). A high-density plastic liner is placed over the clay and a drainage layer is installed over the liner. The liner system must meet all state and federal regulations.