Synthetic turf fields can be played on essentially 24 hours a day, seven days a week, in conjunction with an appropriate field maintenance plan. Synthetic turf fields are beneficial when natural grass fields need time to recuperate after heavy use or are saturated from heavy precipitation events.
Synthetic turf fields require maintenance practices that differ from natural grass management. If a facility has both natural grass and synthetic turf fields, proper maintenance equipment will be needed to meet the needs of each type of field. Sports field managers should be well acquainted with the specifications of the synthetic turf to ensure it performs and is maintained appropriately.
Regulatory Issues
Stormwater management requirements and drainage issues require consultation with local regulatory authorities. Drainage regulatory requirements for a synthetic turf field vary from one jurisdiction to another and will depend in part on whether the synthetic turf field is considered a pervious or impervious surface. The ASBA publication Sports Fields: A Construction and Maintenance Manual (2014) includes the following information on different regulatory scenarios:
In some parts of the country, permitting authorities consider synthetic turf fields to be impervious, like asphalt. Therefore, perimeter drainage must be designed to collect and handle all water, including anything falling on the field itself.
In some jurisdictions, synthetic turf will be considered porous and the base and compacted subgrade will be required to handle a specific amount of precipitation.
Some jurisdictions require the drainage plan handle a specific amount of stormwater, i.e., the 10-year average precipitation, two years total precipitation or even the precipitation caused by a 100-year storm.
Other issues that may arise during the permitting process include concerns related to the following: exposure to infill materials (e.g., crumb rubber); potential leaching of chemicals to the environment; and disposal of synthetic turf components at the end of their life cycle. Crumb rubber is recycled rubber produced from scrap tires. The rubber contains a range of organic contaminants and heavy metals that can volatilize into the air and/or leach into the ground, posing a potential risk to the environment and human health. A limited number of studies have shown that the concentrations of volatile and semivolatile organic compounds in the air above synthetic turf fields are typically not higher than ambient concentrations, while the concentrations of heavy metals and organic contaminants in the field drainage is generally below regulatory limits (Cheng et al, 2014). Human health risk assessments indicate that athletes playing on synthetic turf fields with crumb rubber infill do not face any health risks (Pronk et al., 2020) and that exposure to the components of crumb rubber do not exceed EPA guidelines (Perkins et al., 2019). With respect to any disposal limitations, the sports field manager should review any local ordinances and monitor any state-wide restrictions.
Planning and Design
A number of people are involved in the selection process for determining the best installer and manufacturer for a new synthetic turf field. The sports field manager should be part of the team and should be aware of all the data needed to understand the synthetic materials, the warranty, etc. The use of design professionals and certified builders with demonstrated expertise and success in the development of synthetic turf systems is highly recommended and will increase the likelihood of a successful project.
Many of the same planning and design principles for natural grass fields (as discussed in the Planning, Design and Construction chapter) are relevant for the planning and design of a synthetic turf field. In addition, when considering installing a synthetic turf system, several selection criteria should be discussed by the project team, such as:
Who is the end user of the field (professional, college, high school, parks and recreation) and what are the needs?
What is the climate where the field will be located (tropical, arid, temperate, etc.)?
Is the proposed site appropriate for a synthetic turf field (i.e. not a floodplain)?
Is the installation of a synthetic turf field financially feasible?
Is the selection of a synthetic field cost effective for the intended use with respect to installation, maintenance, and eventual disposal?
Are the maintenance requirements described in the warranty understood and can they be followed?
Is there a program/budget for replacing the synthetic field at the end of its life?
Is there an understanding of the life cycle of different components (e.g., pads, drainage, infill) and options for recycling, reusing, or repurposing these components?
Base System
The stone base of a synthetic turf system is critical to the overall performance, drainage capabilities, long term surface stability, and planarity of a synthetic turf field. The components of a standard base system include the following:
Native sub-grade soil
Proper soil stabilization
Base stone and finish stone
Stone/soil interface
Drainage pipes
Peripheral drainage elements
Drainage and shock attenuation pads
Designing and building a stone base must balance the maintenance of the base’s stability at an optimal level while preserving the whole system’s percolation and water transmission properties.
Drainage
A synthetic turf drainage system encompasses the synthetic turf fibers and infill, base, drainage water evacuation system and, ultimately, the municipality’s stormwater/runoff collection points. The ASBA publication Sports Fields: A Construction and Maintenance Manual (2014) includes the following considerations for evaluating drainage system design:
Specific use or uses of the field
Local climate
Availability and cost of materials
Quality and characteristics of local stone
Financial resources and commitment of the owner
Time constraints for field construction
Annual amount and intensity of rainfall
Local codes and regulations regarding stormwater management.
The drainage design specifies pipe diameters or the sizes of flat drains, locations and distances of laterals, collection systems, and storm sewer tie-ins for the drainage system. Once constructed, an infiltration test should be conducted to verify that the entire system meets STC minimum infiltration rate standards of 14” per hour.
Surface Drainage
Surface grading is critical in the design of a synthetic turf surface. Typically, crowns can be kept at a minimum (not exceeding 1% slope, depending upon site conditions and needs), as drainage relies more on percolation than it does on surface runoff. A crown of 0.5% is found on many, if not most, professional synthetic turf sports fields (Goatley, 2008). It is also preferable to maintain relatively mild crowns so that there is as little lateral displacement as possible of the synthetic turf infill during intense rain events.
Synthetic Turf Field Installation
When a synthetic turf field is selected, it must be installed by experienced professionals specializing in synthetic turf field construction. It is highly recommended that the contractor be certified through the American Sports Builders Association as a CFB and that they reference the STC technical guidelines for installation and maintenance of synthetic turf athletic fields.
Synthetic Turf Maintenance
The maintenance program for synthetic turf depends on the climate, amount of use, the level and kind of sports played, the type of synthetic turf, and the quality of construction. The Synthetic Turf Council (STC) publishes Guidelines for Maintenance of Infilled Synthetic Turf Sports Fields (2013), which augment, but do not replace, the maintenance requirements and procedures provided in the warranty for the field and installation. Manufacturers’ specific recommendations for maintenance should always be followed to avoid invalidating the warranty. However, typical maintenance activities could include:
Checking and replenishing the infill level, especially in high use areas.
Sweeping and dragging to keep the carpet fibers in an upright position.
Troubleshooting for common problems and minor repairs, such as seam repair.
Grooming to loosen and redistribute infill as needed.
Walking the field and noting any loose fibers, seam issues, divots, and uniformity in the carpet.
Removing debris.
Cleaning with solvents and cleansers for difficult to remove items.
Weed Control
Weeds can occur on synthetic turf, as windblown dust can foster their growth. Organic infills have more issues with weed control than does rubber. When weeds occur on synthetic turf, sports field managers should refer to the manufacturer of the synthetic turf system for appropriate methods of weed control.
Winter Maintenance
Like natural grass fields, synthetic turf systems can freeze during the winter. When the surface is frozen, play should be delayed until it thaws. For synthetic turf fields, snow can be removed in accordance with the manufacturer’s warranty. STMA publishes recommendations in Snow Removal on Natural and Synthetic Athletic Surfaces.
Field Safety
Field Surface Temperatures
High field-surface temperatures may be experienced by athletes using synthetic turf fields on clear, sunny, and hot days. One study published by Penn State has shown maximum surface temperatures during hot, sunny conditions averaging from 140°F to 170°F (Serensits et al., 2011). In comparison, natural grass fields rarely exhibit surface temperatures above 85°F, regardless of air temperature.
Dangerous temperatures occur at the surface, which can increase the chances for heat related stress in athletes. Synthetic turf fibers radiate heat, which can be transferred through an athlete’s foot and must be dissipated by the body. While watering the field cools the synthetic turf surface, temperatures rebound often as quickly as 20 minutes after water is applied. Therefore, application of water is deemed an ineffective method of cooling. Various alterations in the synthetic system, such as organic infills, have been tried to ameliorate surface temperatures. Most only lower surface temperatures by approximately 10°F to 20°F, and surface temperatures will remain significantly higher than natural grass fields when exposed to direct sunlight. Though synthetic turf fields heat up quickly under clear, hot, sunny conditions, the fields do not act as a heat sink. While the surface can have very high temperatures, the air temperatures measured two and five feet above the surface are typically only 5°F to 10°F higher than ambient air temperatures. Heat is not stored because synthetic turf fibers reflect solar radiation and the infill acts as insulation limiting transfer of heat into the system. Therefore, at night or under cloud cover, surface temperatures quickly approach the ambient temperature.
During clear, sunny conditions, it is suggested that sports field managers, coaches, and trainers monitor heat index and surface temperatures and make appropriate adjustments to practice and game schedules. It is strongly recommended to use an infrared thermometer to easily monitor surface temperatures.
Field Hardness
The hardness of a surface has been identified by numerous entities as an important parameter of athletic surfaces. Gmax testing, also known as impact testing, measures the shock attenuation of both synthetic turf and natural turfgrass athletic fields. Surface hardness is measured by dropping a weight (referred to as a missile) from a fixed height onto the playing surface. The missile contains an accelerometer that measures how fast the missile stops once it hits the surface. A numerical value, referred to as Gmax, is then generated. A high Gmax value indicates the missile stopped quickly and the surface is harder than a surface with a lower Gmax. Harder surfaces may influence athlete injury. Gmax should be tested at numerous locations across the field, with special attention being paid to high-use locations, such as mid-field areas and goalmouths. At a minimum, testing should occur yearly, but more frequent testing is desirable as field conditions may vary throughout a season.
Various measuring techniques have been developed to evaluate playing surface hardness. ASTM International has designated the ASTM F-355 Missile A device in ASTM F1936-19, Standard Specification for Impact Attenuation of Turf Playing Systems as Measured in the Field. ASTM F-1936 states that the maximum limit for a playing surface is 200 Gmax using Missile A. According to ASTM, values of 200 Gmax and above are values at which life-threatening head injuries may be expected to occur. STC recommends Gmax not exceed 165 Gmax for the life of the field when using the F-355 Missile A device.
The National Football League uses the F355 Missile D device, typically referred to as the Clegg Impact Tester (ASTM F-1702). If any location on the field measures above 100 Gmax using the Clegg, steps must be taken to reduce surface hardness and the field must be re-tested prior to use.
World Rugby uses the F-355 Missile E device to measure head injury criterium (HIC) on synthetic turf. To meet World Rugby standards, a synthetic turf field must measure below 1,000 HIC from a 1.3 m drop height.
Typically, the most effective way to mitigate surface hardness issues is the application of additional infill (i.e., crumb rubber) via topdressing and grooming. Infill depth should be regularly monitored to maintain the manufactures’ suggested minimal depth.
Synthetic Turf Best Management Practices
Include the sports field manager as part of the team from the planning stages for a synthetic turf field project.
Include regulatory issues in the decision-making process.
Include life cycle considerations (such as expected lifespan of the components, ability to recycle components, etc.) as part of the evaluation process when selecting a synthetic turf field manufacturer.
The contractor installing the synthetic turf field should be certified through the American Sports Builders Association as a CFB and reference STC's Guidelines for Maintenance of Infilled Synthetic Turf Sports Fields.
All field maintenance should be carried out in accordance with the warranty.
Develop a maintenance schedule that specifies maintenance routines, such as annual, monthly/weekly, and pre- and post-game maintenance activities.
Use only methods indicated by the warranty for weed control, if necessary.
Monitor the field temperature, preferably with an infrared thermometer, on hot, sunny days.
Postpone or reschedule practice sessions or games to protect human health when the surface temperature is too high or cannot be maintained adequately.
Measure field hardness annually (at a minimum) to ensure the level of hardness is lower than the level specified by ASTM standards.
Use an independent or third-party tester to measure field hardness at least annually.
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