Tempe has spent $110,000 to treat bad water at Town Lake this year, an effort that has barely kept the water safe enough for the world-class swimming events held there. Despite numerous chemical treatments this year, the city has canceled one event, moved another to a pool and shifted others to parts of the lake with better water.
Officials are working to keep water quality in check so a few remaining fall events can take place, including Sunday’s Soma Half Iron Triathlon, which is expected to draw more than a thousand athletes from all over the country.
Athletes, too, hope everything will go as planned. Commodore Mann, a 36-year-old triathlete from Mesa, said his only concern about high pH levels was that it could disrupt events at Town Lake. In fact, he said he’d rather swim there than just about anywhere else — high pH or not.
“This race is billed as one of the biggest in the country, and high pH levels aren’t going to keep anyone from wanting to get in the water,” Mann said. “It’s terrible if you have an event that includes running, swimming and biking and all of a sudden it becomes a dualathlon.”
As part of a long-term solution, the city is planning a bypass effort, using pumps to channel millions of gallons of bad water around the lake to stop the contamination and keep the lake’s chronically high pH levels safe enough for swimmers. The city hopes to start pumping this spring, before warm weather brings a return of swim events.
“That would change everything,” said Basil Boyd, a water resources hydrologist for the city.
This problem is rooted in something that initially seemed a perk — heavy rainfall nearly two years ago that caused water to pool east of Town Lake.
The water poured over the lake’s east dam and into Town Lake. The water was fine when the river flowed heavily in early 2005. But when the river’s flow dwindles to a trickle, bacteria growth skyrockets and pushes up pH levels.
Tempe only allows swimming when pH is 9.0 or lower because higher levels could cause eye and skin irritation. The lake was below the limit most of the time until 2005. But since then it’s been near or above the threshold for months at a time.
The Environmental Protection Agency recommends pH levels of 6.0 to 8.5 in drinking water, but it doesn’t regulate it. It’s considered a secondary water contaminant whose impact is aesthetic.
The city can lower the pH by dumping hundreds of gallons of algicide in the lake, which usually lowers pH by 0.2 or 0.3 for up to a week, Basil said. The city has done 11 treatments this year, at a cost of about $10,000 each, and expects to do three more treatments this year.
The pH level climbed to 9.2 early this week, but a midweek treatment was expected to bring the lake just below 9.0 for this weekend, Basil said.
The city tried to deal with the problem this spring by bypassing the lake using an existing storm drain. The pump moved 3.5 million gallons a day, but that wasn’t enough.
“It just didn’t really seem to have any effect,” Basil said.
The problem was that part of the pipe is just 12 inches in diameter. The city is looking into the cost of replacing the narrow section with a 30-inch pipe, said Nancy Ryan, the Rio Salado project manager. That should allow the city to pump 15 million to 20 million gallons a day, she said, easily enough to keep water from spilling into Town Lake.
The pH could still rise to 9.0 occasionally, Basil said, but stopping the flow of water should allow the city to keep pH in check with occasional treatments.
Swimmers are aware of the pH issue, said John Hyte, a triathlete from Mesa. He’s competed in about 20 triathlons in different places and swam in Town Lake about 12 times, and has never been bothered by the water.
The lake’s water is much better than San Diego where diesel fumes from boats makes it nearly impossible to breathe, he said.
Hyte said the pH isn’t an issue for competitive swimmers.
“It tends to be low on the priority list,” he said. “They’re thinking, ‘Is the guy next to you going to beat you up as he tries to swim past you?’ It gets kind of violent out there.”
Soma Half Iron and Quarterman triathlons What: The Half Iron Triathlon is a three-part race that includes 13.1-mile run, a 1.2-mile open swim and a 56-mile bike trek.
When: Starting at 6:30 a.m. Sunday
Where: Tempe Town Lake