The species in question are the Austin blind salamander, the Barton Springs salamander, and the Comal Springs dryopid beetle. In his letter to the EPA, USFW field supervisor Adam Zerrenner recommended that careful attention be paid to the "direct and indirect effects of the proposed permit" on the imperiled species.
"Clean water is essential to the survival of these aquatic species and to maintaining a viable habitat," Zerrenner said in the letter. "These species are unique to the local area and are supported by the aquifer recharge water that enters the Edwards Aquifer."
The letter states that discharge of municipal wastewater presents significant risk to water quality because of elevated nutrients and contaminants which are not removed during the treatment process. It lists examples such as pesticides, pharmaceuticals, personal care products, and inorganic pollutants—all of which pose threats to aquatic life, according to the USFW.
The letter also pointed to the risk associated with untreated sewage accidentally making its way into the creek. Richard Beggs, board member with the Protect Our Water, an organization which aims to protect Onion Creek from pollution, said this was especially significant.
"Of particular interest were their comments on [the impact of] untreated sewage due to mechanical failure or emergency discharge as well as many contaminants that impact aquatic life but are not removed in the treatment process," Beggs said. "This important letter is one more example of why Dripping Srings should seek a more responsible, no-discharge solution."
Both salamander species inhabit Barton Springs, which Beggs said obtains 34 percent of its water from Onion Creek. In the letter, Zerrenner pointed to the critical impact the wastewater would have on the species' habitat.
Last September the city of Dripping Springs submitted a draft permit to the Texas Commission on Environmental Quality, or TCEQ, requesting permission to release 995,000 gallons of wastewater into Onion Creek per day. In November, dozens of north Hays County residents gathered at a public hearing in Dripping Springs to oppose the permit.
The EPA has alleged that the TCEQ inadequately analyzed the draft permit, and has requested more information on the commission's Tier 2 analysis, which determines the impact the wastewater would have on water quality.
According to Ginger Faught, deputy city administrator for the city of Dripping Springs, her office has known about the USFW letter since December.
"It is part of the process," Faught said. "We will work through this like we have worked through other issues."
Faught said that the TCEQ has not yet issued a formal response to the EPA's comments on the draft permit.
The Dripping Springs Chamber of Commerce voted to support the city's application for discharge on Feb. 21.