Costa Rica’s soccer field is filled with wastewater and already the

The Costa Rican football field has at times looked like a spaceship landed for a visit.

From the grass volleyball courts, to the boulder pile overlooking the artificial pitch, to the man standing on the Lagoa Paraíso next to one of the training pitches, the Costa Rican National Stadium has lots of layers that lend it the appearance of a space station. It’s the home of the national team and a popular soccer and volleyball venue for tourists.

But it’s also a large sewage treatment plant. A naturally occurring watershed known as the Rio Cuarto flows south and west from the Metropolitan District of San José. At least 300 million gallons of water flows over the stadium’s pitch each day. Every soccer game there also incurs about 100,000 gallons of waste water. More than a third of the water discharged into the Rio Cuarto comes from the fields.

“Every day there is 10 to 15 million gallons [of waste water] released into the environment,” said Leneir Ortiz, a director at the National Superintendence of Wastewater (SENURICON).

Construction workers clad in blue sheeting pull out other man-made materials that have built up on the field like slides, tunnels and rails. The aging, archaic infrastructure these systems are based on dates back to the days when the field was built in 1957.

The outdated pipes are connected to six sewage treatment plants about eight miles apart. Many are in disrepair, but SENURICON estimates that 69 percent of the plants are in good shape. Of the 48 sites with problems, 49 are due to lawsuits against the state or private companies.

When Stanford University researchers started researching sewage treatment techniques about 15 years ago, they discovered that Costa Rica had some of the most advanced facilities in the world. And the plants were sharing a few characteristics.

One of them was that they were built atop environmentally sensitive land or municipal waste sites. Another shared similarities with the original farm fields and human settlements around them — they were arranged with the goal of collecting more water than would be delivered out of the city. And perhaps most importantly, they acted like a sponge to drain water that wouldn’t naturally be flushed down into the water that flows out of the mountains every day.

So researchers sent teams of students to play on Costa Rica’s sewage treatment plants to see if they could change their functions. They discovered that Costa Rica’s average 500-millimeter membrane filter is effective at trapping and filtering out 3,000 to 4,000 pounds of materials from a river each year. They had also shown that simple pump-and-catch methods of precipitation could collect as much as two to three times the amount of water that flows out of the ground.

For instance, water that enters a waterfall can collect up to eight times its initial volume. The water captured from the Kachira dam on the Corcovado River in Colombia is even more impressive: up to 83 times the initial volume.

In the United States, nearby communities rely on sewage systems that drain into rivers every day. This lack of monitoring has resulted in problems in some places, particularly in New Jersey, where there has been a high risk of e-coli transmission and contamination of surface waters. But few of these pollutants have escaped into the Rio Cuarto river in Costa Rica.

We’ve had a presence in the Rio Cuarto since about 2006. (In 2002 we started testing treatment plants and started planning the first water-inspection team that has been operating from here. )

We’ve been able to collect an entire year’s worth of water just from upstream in the year that we have been here. And we found that there is literally no pollution in the Rio Cuarto river, zero. So we see an incredible amount of waste water coming off the fields of the National Stadium. But that waste water, if it’s not able to make it through the treatment process and find its way into the river, falls into a very deep sewage canal. The canal fills up with bacteria, bad chemistry that starts to pollute the riverbed and the Conejo River. And we’ve seen that pollutant levels are constantly increasing.

Local water pollution is a serious problem, but let’s be clear, Costa Rica’s sewage treatment is a worldwide leader in sustainable water capture. The country has performed so well that it recently received an honor of the 2016 Sustainability Symposium from the United Nations Environment Program.

And the results of this wastewater capture are found not only in the river but also on the lake near the stadium. Almost 50 percent of the water taken from the lake from 2010 to 2015 is now treated. The technology was tested by returning the water to the stream that flows under the stadium.

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