above the gravel that helps keep the root zone moist during dry conditions. A drainage system is installed below the gravel to carry excess water away from the field. ASTM F2396 methods are more flexible in design and instead of a set specification gives guidance on selecting sand for a more varied range in construction methods. For example, with or without a gravel drainage layer, with or without peat and/or soil amendment, and profile depth variance from 8 to 16+ inches. Aeration and topdressing Aeration on a sand-based system is used more to control the thickness of the thatch layer than to relieve compaction. Thatch layers are the accumulation of decomposed vegetative parts of grass plants like stolons and rhizomes at the surface level. A thick thatch layer on a sand-based athletic field may prevent nutrients and water from reaching the soil. Further, fertilizers, fungicides, and insecticides can not penetrate the surface and reach the soil. This can obviously be devastating if a field is consumed by a soil borne disease or insect. Water penetration can also be deterred by a thick thatch layer. When there is a thick mat of organic matter near the surface of a field a second perched water table will form. This will cause roots to stay in the top couple of inches of soil because they do not need to search for water at greater depths. Without a deep root system, a field can become unsafe due to footing issues. One method of thatch control is core aerification. This is the process of tilling the field with hollow tines to remove thatch from the surface. Tines used in aerification are hollow, measuring a half inch in diameter, and typically reach a depth of four inches into the turf. If the holes are on 2 inch center, 36 holes will be punched per square foot. After a field is aerified, the cores can either be raked up and removed, or left on the surface to break down. Once a field is aerified, and there are holes in the surface, a field should be topdressed with the same sand that was used in the construction of the field. Refilling the aerification holes with sand improves the macroporosity of the soil and allows better penetration of water. This will allow the turf manager to water deeper and therefore improve the root system. Introducing sand into the thatch