Windrow composting is a simple, but slow composting process. The material is piled up in heaps or elongated heaps (called windrows). The size of the heaps ensures sufficient heat generation and addition of bulky materials, passive or active ventilation or regular turning ensures aeration. Systems with active aeration by blowers are usually referred to as forced aeration systems and when heaps are seldom turned, they are referred to as static piles. Leachate control is provided by a sloped and sealed or impervious composting pad (the surface where the heaps are located) with a surrounding drainage system.