Oudoor Areas

Synthetic Turf That Wins for the Environment

It's important that fields be designed and constructed to not only protect athletes and budgets, but also the environment.

• By Jeff Bresee
• 10/01/19

In 2017, CEI was hired to work with Lake Travis ISD in Austin, Texas to design synthetic turf systems for four separate schools, as well as improve their 400-meter tracks. The schools — located in different city or unincorporated county jurisdictions in Lakeway, Austin, Bee Cave and Travis County — needed separate permits.

Each governing body had its own strict environmental standards. As the permitting processes began, each jurisdiction raised concerns whether heavy metals like lead and zinc would leach into the water system from the styrene-butadiene rubber (SBR), or black tire rubber granules, used as an infill in the turf system. Each jurisdiction also ruled that synthetic turf is an impermeable surface and that detention volume would be required.

As the school district’s budgets for these fields were not sufficient to include new water detention and quality ponds, nor was it enough to utilize more expensive infill materials that do not leach heavy metals, our team was tasked to design a system that would resolve permitting concerns while meeting the project budgets. Our solution was a breathable, crushed limestone underdrain system set on a geotextile fabric layer with a compacted, structural base.

Our design for each field’s underdrain system utilized washed, crushed limestone to provide underground detention in the air void space of the stone. At the same time, the gradation of the stone and its configuration with the storm water collection systems was designed to maximize contact between the stone and the water and thereby maximize water quality.

Field testing was conducted to demonstrate that the crushed limestone had a void ratio above 45%, which was needed to provide adequate detention volume for a 100-year storm beneath the field. Studies from other industries such as mining were used to demonstrate that crushed limestone is an effective means of removing zinc and other heavy metals from water, with up to 90% removal when designed to optimize contact time between the stone and water.

By using this design, we successfully demonstrated that the granular-infill synthetic turf systems are self-sufficient and self-treating systems that do not require separate water detention and water quality ponds even when SBR rubber is used as an infill media. After a 14-month permitting process, the governing bodies had each accepted the design and granted permits and each of these fields are presently constructed.

This is a significant precedent. Over the past decade, multiple studies have been conducted to determine if SBR rubber infill in turf poses an environmental threat. Each study has concluded that this type of turf does leach lead (within EPA limits) and zinc (sometimes above EPA limits) to storm water. However, none of these studies make definitive conclusions regarding the environmental threat, but rather only conclude that more research is needed. Thus, successful permitting for these projects in the Austin, Texas area is significant because of the decisions made after such extensive review processes.

Many schools, universities and private sports entities have converted grass fields to granular-infill synthetic turf and many more are in the process. This product is proven in performance and long-term cost effectiveness, and so this trend will continue. As this happens, it is important that fields be designed and constructed to not only protect athletes and budgets, but also the environment. We have shown that this can be done and, if properly designed, the turf system will not only maintain water quality, but it will improve it.

The environmental threat of zinc and lead in storm runoff from synthetic turf is real but well-maintained grass fields pose threats to the environment as well. Grass fields harm the environment by means of the pesticides and fertilizers they require. Storm runoff from a newly fertilized grass field can contain levels of nitrogen, phosphorus and potassium that do not meet typical sewer treatment water standards. Runoff from granular-infill turf fields do not have these pollutants present. A properly designed turf field can be a winner for owners, athletes and the environment.