SAWS considers Lake Mitchell Wetland Pilot Project a success

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When Gregg Eckhardt floated the idea of ​​cleaning up the shores of Lake Mitchell with man-made wetlands more than two and a half decades ago, he wasn’t sure the project would take off.

The once very smelly site on the south side between Texas A&M University-San Antonio and the Mission del Lago golf course was once a place where the city of San Antonio stored raw sewage and then partially treated sewage to be used for irrigation.

Although new sewage stopped being added to the lake in the 1980s, the residual sludge caused algae growth and changed the pH levels of the water. Because of this, every time the water overflowed the banks, the SAWS violated the sewage treatment plant permit it had obtained for the lake in 1974.

In 2016, the United States Environmental Protection Agency issued an administrative order calling on the SAWS to develop a plan to deal with the periodic overflow. It was then that Eckhardt, a senior production and processing operations analyst at SAWS, again brought up the idea of ​​constructed wetlands to his administrative peers at SAWS. The wetlands would act as a filter, cleaning up the water that escaped before it reached the nearby Medina River, Eckhardt explained.

Now, six years later, SAWS has deemed its one-acre pilot project successful and is preparing to expand the artificial wetland for up to 100 acres on the southern shores of Lake Mitchell. It’s a dream come true for Eckhardt and his partner on the project, Dan Crowley, director of government relations at SAWS.

“Pardon the pun, but this is a green solution to a green problem,” Crowley said with a smile.

How did we come here?

Traveling to Lake Mitchell today, one must first pass under a large iron gate marked “Mitchell Lake swamps” on a white dirt road. The large blue lagoon is surrounded by cattails and tall brush. Dozens of wooden stumps protrude from the water, birds perched on several.

While Lake Mitchell is rumored to be one of only two natural lakes in Texas, the thousands-year-old body of water probably wasn’t actually a lake when it was discovered by explorers. in the 1700s, Eckhardt explained during a recent visit to the pilot wetland. Named by the first Spanish settlers the Los Patos Lagoonor Duck Lagoon, it’s described in historical journals as wading and was likely closer to natural wetlands, Eckhardt said.

In 1839, Asa Mitchell purchased 14,000 acres in what is now south San Antonio, which included what would become Lake Mitchell. It quickly became a popular spot for birdwatching and duck hunting; the protruding stumps and stems that stand in the lake today still mark many old duck caches.

However, that all changed after the city purchased the lake in 1901 and began directing raw sewage into the lake.

“Legend has it that the dam was built from the rubble of a flood in downtown San Antonio around the turn of the century,” Eckhardt said. “If you walk over the dam today, you find pieces of bathroom tiles and such.”

By 1971, the area had become so smelly and the lake so overloaded with organic material that local residents sued the city. The complaints were taken to the Texas Legislature, where state government officials became involved.

“They decreed that there would be a report prepared on what to do with Mitchell Lake…a remediation plan,” Eckhardt said. “So in 1974 Mitchell Lake was licensed as a sewage treatment plant.”

A year earlier, the city had declared the lake a refuge for waterfowl and shorebirds, but with a sewage permit, the city was still using the lake for sewage disposal, until 1987. SAWS assumed responsibility for the 600-acre lake in 1992.

While SAWS was able to better regulate and treat the lake under a sewage permit and later, in 2020, a stormwater permit, lake pH levels still varied widely due to algae.

After the EPA issued its administrative order on permit violations, SAWS commissioned a study weighing various solutions.

Eckhardt said SAWS wanted to solve this problem in the most environmentally friendly way possible, because despite the algae, the lake had become a paradise for birds. Located along the Central Flyway, bird enthusiasts have recorded over 300 species at the site. The lake is also home to a bird sanctuary, Mitchell Lake Audubon Center, where ecotourists come from all over the world to visit. SAWS didn’t want to drastically alter the environment for these birds, Eckhardt said.

“So what we proposed to the EPA was a constructed wetland under the lake,” he said. “And they liked the idea so much that they ordered us to do it.”

Gregg Eckhardt, Senior Generation and Processing Operations Analyst at the San Antonio Water System, stands in a future wetland cell below Lake Mitchell. Credit: Scott Ball/San Antonio Report

A successful pilot

While wetlands as a water treatment system are quite common across the country, no one has ever tried to use wetlands to filter a body of water quite like Lake Mitchell, with its wide variation in daily pH levels due to its algae and nutrient rich state. , Eckhardt said.

Therefore, a small-scale pilot.

In 2019, SAWS planted bulrush, a pH-resistant native freshwater plant, on 1.3 acres on the western shore of the lake and made modifications to a dam that will allow the utility to better control the water levels. The utility has spent about $8 million on the project so far, SAWS’ Crowley said, including $4 million for 283 acres south of the lake.

After 18 months, SAWS declared the pilot a success.

The test wetland allowed SAWS to experiment with how much water wetlands could effectively handle before becoming oversaturated: between 2 million and 7 million gallons per day, Eckhardt said.

On a large scale, fully constructed wetlands will be able to effectively filter hundreds of millions of gallons per day, he added.

San Antonio water system officials outline preliminary plans for future wetland project at Lake Mitchell.
SAWS officials are reviewing preliminary plans for the future wetland project at Lake Mitchell. Credit: Scott Ball/San Antonio Report

The bulrush has also taken off and is actively spreading around the lake, which is exciting for environmental scientists like Eckhardt as it creates more habitat for local species, like roseate spoonbills, white pelicans and cuckoos to yellow beak.

“We learned that it will work,” he said. “We were very excited about it.”

A look ahead

SAWS attention has now turned to achieving the large-scale wetland. A third-party design process is underway, including for a new weir and a paved cycle and walking path above the old dam along the lake.

The new weir is necessary so the SAWS can control the amount of water filtering through the wetlands, Eckhardt explained. Although the existing dam and weir are still standing, they are 120 years old. There are plans to channel water from the lake away from the historic weir to preserve it for visitors to observe.

“When we did the first phase, we had to do historical and archaeological surveys and what we learned was that we have four resources there that are eligible to be listed on the National Register of Historic Places,” Eckhardt said. “The spillway is part of it.”

SAWS plans to offer support to the Texas Historical Commission to mark the weir on the national register, Eckhardt said.

The utility plans approximately six “cells” or wetland areas between the lake and the banks of the Medina River. The utility is still in talks with some private landowners about acquiring land for the project, Crowley noted, although he added that SAWS was confident about how those discussions were going.

The wetland project isn’t the only improvement at Lake Mitchell. In the most recent bond, San Antonio voters approved $6 million for habitat and ecosystem restoration, new connections to existing hiking and biking trails, and potentially a center of reception. On behalf of SAWS, Crowley recently secured a $3 million appropriation from Congress for a lake ecosystem restoration study.

“So yeah, there’s a lot of great things to come for Mitchell Lake,” Eckhardt said.

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