An email came across my desk in August, sent from a gentleman in California whose local high school synthetic football field was deemed too hard. It had failed nine out of ten field hardness tests and so had been taken out of commission for the fall playing season. This had caused some ripples in the community. The field was 11 years old and the questions were: Was it possible to rip out the synthetic and install a grass field in time to save the season? And what would that entail?
My initial response is yes. It’s always possible to rip out the field and replace it with a natural grass field, but that’s not a quick or cheap fix. It would involve removing 0.5 millions lbs. of sand and crumb rubber infill and finding somewhere to accept it as waste, removing the carpet and gravel base, salvaging or installing irrigation and drainage systems, bringing in new rootzone material, grading it, and covering it with thick-cut sod. The timeline for this would depend upon many factors, like availability of local field construction companies and availability of thick-cut sod. The renovation would take several weeks, cost a lot of money and might only result in a couple of saved games.
Looking at this problem a little deeper, it would have been good to know why they wanted to remove the synthetic field. Is it because players and staff prefer natural grass? That was the case for the Baltimore Ravens where the team (and field manager Don Follett) voted to switch back to natural grass in 2016. Don felt, as I do, that the improved turfgrass varieties available now, plus advances in technology and maintenance equipment, means that natural grass fields could be very successful, regardless of local environmental conditions. If that is the case in the CA situation, a natural grass installation should definitely be planned and budgeted for, especially since the field is 11 years old and has come to the end of it’s life anyway. But if they really like the synthetic and are only looking at this option because they want a quick fix this fall, maybe replacing just the carpet and infill is the better option. It would still take time to rip out and dispose of the infill and carpet, then 2-3 weeks for carpet manufacture and two to three weeks for installation. The field’s age and its being too hard for safe play means both of these options need immediate, deep discussion. Both options will be costly and will need to take into consideration school preference, field usage and available resources.
In retrospect, it would have been easier to monitor field hardness and have those conversations when the field was 5 or 6 years old, or mid-life. Regular annual or bi-annual Gmax testing with either the F355 (Gmax <200) or Clegg (Gmax <100) would have shown the increase in field hardness before it was too late to do anything about it. There are also recommended maintenance procedures to prevent and control field hardness. Regular grooming and periodic topdressing with fresh infill material are both key operations. Keeping infill levels at the correct depth is safer for players and extends the life expectancy of the field by a couple of years. Since there is such a strong correlation between infill depth and surface hardness, it’s imperative that the infill depth be measured regularly. An infill depth gauge costs about $30. Infill depth should ideally be at least 1 ¼ to 1 5/8 inches deep. Definitely no less than one inch in depth.
Both ASTM and the Synthetic Turf Council recommend testing infill depth on the field in several locations, as well as inlays, painted lines, seams and high traffic areas like lacrosse creases. If the infill depth is less than 1 inch in depth, it can increase surface hardness. A second problem arises if the field is old and the turf fibers are worn down. If fibers are not long enough to topdress, it’s impossible to add more infill. This may have been the case in California.
A third scenario I have encountered first hand, mostly in the urban environment, is that the fields get clogged with silt blown in from the local environment, particularly if there is construction nearby. The silt and other fine mineral particles can settle down in the fibers and create a hard compacted layer.
This brings me to my last suggestion. About half way through the field’s life, if Gmax readings are indicating a field hardness issue, it’s possible to have a full depth renovation. This involves removing most of the infill, deep grooming and replacing with new infill. One company who does full depth renovation uses high-pressure air to blast the infill out, which is then vacuumed up. This procedure can generally lower the Gmax value by 30-40%. One example given was a Gmax of 176 lowered to 144. Given the age of the field in California, I don’t believe this would have been the most economical option, even if the turf fibers were in good enough shape and deep enough to accept infill, which I doubt.
In summary, monitoring Gmax and infill depths and carrying out regular maintenance will prolong the life of the field and keep it safe for the athletes. At some point though, the field will still come to the end of its life, either by being worn out or by exceeding the Gmax limit. The goal then is to plan for that happening and to have a budget and a strategy in place so that it doesn’t catch anyone by surprise.
Thanks to Don Follett, Senior Director of Field and Grounds at The Baltimore Ravens, and to Allen Verdin from The Motz Group for their insights. Photo of Brian Gimbel taking infill depth measurement taken by Pam Sherratt.