A turf expert addressed Vashon’s school board Thursday night and laid out the benefits and drawbacks of synthetic turf and grass for the Vashon High School field.

The presentation was part of the board’s ongoing information-gathering and planning efforts ahead of a second attempt to pass a bond to repair and replace some the district’s athletic facilities. The board has not determined a date for a final proposal, or for a bond election.

Thursday’s presentation took place during a regularly scheduled meeting and was open to the public, but only about six people attended.

Board chair Bob Hennessey said Friday that the talk by Dave Anderson, principal engineer at Seattle’s D.A. Hogan architecture firm, left the board with a lot to think about, but was helpful.

“There’s a very complicated number of choices and trade-offs from water use, to overall cost, to having something you can use all year,” Hennessey said. “Absolutely it helps us because we’re getting real data about costs.”

Anderson spoke about three major types of fields: a soil-based grass field, a sand-based grass field and a synthetic turf field, stating from the beginning that soil-based fields are rare in this area due to rocky topsoil that does not drain well and the abundance of wet weather. Vashon High School’s (VHS) current stadium field is soil-based.

For natural fields, he said sand-based are the most popular and can be used in wet weather because they are made to drain.

These sand-based natural grass fields have cheaper installation costs than synthetic turf — the gross cost of installing a grass field is $2.50 per square foot for sod or $1.80 per square foot for seed, while synthetic turf is at least $11.50 per square foot. For VHS’ 100,000 square-foot field, installation costs come to $250,000 for sod, $180,000 for seed and at least $1.15 million for artificial turf.

As for maintenance, while natural grass is cheaper on the initial construction end, it comes with high ongoing irrigation and maintenance costs and necessary closures due to weather and over-use.

Both sand-based grass fields and synthetic turf fields should have the turf layers replaced every 12 to 15 years for grass, or eight to 12 years for synthetic turf.

“With both natural grass and synthetic turf, you need to replace the top layer,” Anderson said.

Replacement costs run around $250,000 to $300,000 for a grass field and $800,000 to $1 million for an artificial turf field.

The McMurray Middle School sports field — which is roughly twice the size of the VHS stadium field — is a 12-to 14-year-old sand-based grass field that, according to Dave Wilke, the school district’s facilities director, is generally used nearly every day for nine hours per day from September to December for island soccer clubs. It is used for lacrosse in the spring (February through May) and closes for seven or eight weeks every summer for maintenance. Its top grass layer has never been fully replaced.

“By the end of the season, it looks bad. It’s thrashed,” Vashon Island School District (VISD) board member Zabette Macomber said.

The heavy use is due to the fact that the field is the only lit field on the island, necessary for the sport during dark winter nights.

“It’s kind of the only option after 5 p.m.,” Wilke said.

But Anderson said that given the field’s age and amount of use, it is one of the best he has seen.

“(That field) is ahead of the vast majority of K-12 schools maintenance-wise,” he said. “With maintenance procedures, you’re (the district) on the right track.”

The maintenance doesn’t come cheap. According to documents from Vashon’s Water District 19, between 2005 and 2014, the school district typically used between 6 and 8 million gallons of water annually, the bulk of that in July and August. Annual water bills exceed $50,000. Wilke said the McMurray field consumes about 60 percent of the district’s total water allotted for field irrigation.

“If you’re not regular with watering during the summer months, it browns out,” Wilke said. “Your hand is somewhat forced if you want to sustain the grass. You have to water through the summer.”

While McMurray sees heavy use, the stadium field at VHS is closed to most community groups and reserved for school football and soccer games and high school-age club lacrosse. Wilke said both a sand-based field and a synthetic field would allow for more activities on the stadium field.

“It sees roughly 50 events per year, including graduation,” Wilke said. “It’s certainly accurate that sand-based would allow for significantly increased use, but it will still be treated with more caution and care because that’s where the show is, that’s where everything happens. No question, that number (of events allowed on the field) would increase by significant multipliers if the field were synthetic.”

According to Anderson, synthetic turf can be used year-round, regardless of weather. The field would not have to be closed for months, and maintenance consists of re-filling infill, a process that takes one or two days.

“Synthetic can be programmed year-round with no restrictions,” Anderson said.

One drawback of synthetic turf is the cost. As mentioned, initial construction costs for a synthetic field can range from $11.50 per square foot to $16.90 per square foot — between $1.15 million and $1.69 million for the entire VHS field — more than double the cost of a grass field, but irrigation is not needed.

The question of irrigation is something that sits heavily with board chair Hennessey.

“Grass is millions and millions of gallons of water. I’ve been wondering if that’s the best use for our limited treated, potable water supply,” he said last week. “Putting it on a sand field that is explicitly made to drain water, that’s a tough nut to crack.”

And while the usefulness and potential water-saving ability of a synthetic field is clear, the issue for some islanders during February’s bond election grew out of the field’s infill — the small particles that are placed on top of the synthetic grass and pressed down between blades to create a grass-like texture — and the potential hazards from it. Crumb rubber — the traditional synthetic turf infill made from ground up tires — is the most commonly used material, but has made headlines in recent years as some have called into question the potential health hazards that could come from inhaling or ingesting the small rubber pieces.

No research has linked cancer to artificial turf, and scientific studies so far are mostly incomplete and inconclusive.

The potential for health hazards exploded onto the national media stage in 2014 when University of Washington Associate Women’s Soccer Coach Amy Griffin compiled a list of nearly 40 American soccer players diagnosed with cancer. NBC News conducted an investigation later that year, reviewing relevant studies and conducting interviews with scientists and industry professionals, but was “unable to find any agreement over whether crumb turf had ill effects on young athletes, or even whether the product had been sufficiently tested,” the NBC article reports. In 2010, the California Office of Environmental Health Hazard Assessment (OEHHA) conducted a study about the safety of crumb rubber and measured chemicals released into the air. The study, funded by the California Department of Resources Recycling and Recovery, found a total of 65 chemicals were released in the air above a 4-year-old field and 85 over a 1-year-old field. However, after being tested for potential cancer risk based on measured air concentrations and assuming continuous, lifetime inhalation by athletes using the fields, investigators say they found “these fields do not constitute a serious public health problem since the risks of health effects are low.”

In June 2015, CalRecycle agreed to conduct a new study on synthetic turf and potential human health impacts. That study is currently underway.

The Environmental Protection Agency, the Consumer Product Safety Commission and the Centers for Disease Control and Prevention have also announced they will study whether artificial turf fields and playgrounds that use bits of recycled tires expose children to dangerous chemicals, Reuters reported in February.

But recycled tire infill is not the only option for artificial turf infill. Other options are more expensive, but include Nike Grind, made from ground-up tennis shoes; natural alternatives such as cork and coconut fiber; silica sand and coated rubber.

“We have two options for grass (soil-based and sand-based), but at least six for artificial turf. It’s not a binary do grass or turf with crumb rubber, it’s much more nuanced,” Hennessey said. “I want to see a robust discussion around this.”

Ultimately, Hennessey said, the decision comes down to community use, not just the school district. Roughly two-thirds of the district’s fields use is by non-school groups, mainly club lacrosse and soccer, he said.

“It makes no sense for us to build a field and wall it off. That’s wasteful,” Hennessey said. “People ask, ‘Why build a Cadillac field when the school only uses it so much?’ That’s why. It’s for the community. It’s everybody’s money.”

Facilities Director Wilke seconded Hennessey and said that a new field that could be used more can take pressure of the community’s other fields.

“If we were to go ahead with a synthetic stadium field, it would not be in a vacuum,” he said. “If we were conscientious and thoughtful, it could help us manage all the fields better. It could possibly remove the strain on the McMurray field and keep it in better shape. Usage on sand-based fields has a direct correlation to replacement.”

The board is planning on holding several public meetings this fall to discuss options and priorities prior to making decisions about the bond proposal. Anderson is scheduled to speak at another meeting in September.

“This isn’t going to be a board decision,” Hennessey said. “It’s a hot-button issue.”