New England Blade – Arthur Eddy, ASLA, LEED AP
Modern synthetic turf fields are highly engineered systems that are made up of several components.  When working in unison, synthetic turf fields can create a safe, high performing athletic surface.  Synthetic systems are typically made up of synthetic turf carpet, an infill and sometimes a shockpad.  This article is going to focus on the importance that infills play in the turf system, how to identify issues and how they need to be maintained.
Infill is part of the ballast that weighs down the turf and fills in between the fibers of turf.  Infills can be made from varying materials whether natural, engineered or recycled products. Along with the turf fibers, the infill is a component that directly interacts with the athlete. Infill can have an impact on how an athlete’s foot reacts to the system, including energy restitution into an athlete’s legs, impact on an athlete’s lower extremity, and how a foot will rotate when making cuts. Appropriate infill levels can also impact the performance of a ball on the field. Infills are carefully mixed and matched with the synthetic turf carpet depending on turf weight, stitch gauge, and fiber completing a system. During installation, systems are typically tested for safety and performance including GMax, Head Injury Criteria (HIC), vertical deformation, rotational resistance, ball roll, and ball bounce.
Because the infill is typically loose in the system, infill can easily be displaced. For systems to perform correctly, the infills need to remain consistent and typically require a ½” or 12mm reveal of fiber.  The depth of the infill will be related to the original fiber length, so understanding the turf system including fiber length is important for understanding the infill requirements. To maintain surfaces that meet their original performance criteria, grooming on a regular basis can assist with over compaction of infills and appropriate distribution. As a rule of thumb, a synthetic turf field should be groomed approximately every 100 hours of use.
Unlike a natural grass field, a synthetic turf system does not reveal signs of wear, like turning brown, thinning, or signs of disease. Typically, when a turf field is showing signs of wear it is already too late. A manager of a synthetic system needs to check infills on a regular basis. An infill depth gauge is a tool that can help monitor areas that need to be addressed. Keeping a log of infill depths can allow appropriate action on the field to take place and help to make sure that you are keeping up on the requirements of the manufacturer’s warranty.
High use areas in fields should be checked regularly. This should occur every other week and before and after grooming. This is critical in the high-use areas as outlined below:

* Football

* Goal line
* Kick-Off Marks
* Extra Point Line
* 15 Yard Line
* Center of the field
* Between the hash marks

* Soccer/Lacrosse

* Penalty Kick
* Corner Kick
* Center Mark
* Goal Mouths
* Face-off spots

Typically, synthetic surfaces overlay multiple sports and high use areas coincide with other sports. This is highly impacted by practice and repetition on the field. High use areas (Figure 1) should receive new infill on a regular basis which can be applied with a five-gallon bucket and swept in with a stiff bristle broom.
Along with safety, the longevity of the synthetic turf is related to infill depths. Fiber can prematurely breakdown when not properly filled. Fiber has memory and when fiber starts to bend at a lower level it exposes the fiber to breaking down at a lower level. When the fiber breaks down, the system no longer can hold infill and the performance and safety of the field can be compromised. If left unmaintained, this can lead to expensive replacement of high use ar...