Local · Trusted · Free
The Morning Impact — your neighborhood's most important stories, delivered every morning.
Study addresses SH 45 SW's challenges
TxDOT: Road could have negligible effect on Edwards Aquifer
By Joe Olivieri
This is Part 2 of a two-part series.
For years, critics claimed building SH 45 SW—a proposed four-lane, 3.6-mile-long toll road—would damage the environment without significantly improving mobility in southern Travis County and northern Hays County.
Supporters have disagreed—they argued a road could be built that did not harm the Edwards Aquifer while providing a needed connection from MoPac to FM 1626.
Both sides had been waiting for the results of the Texas Department of Transportation's environmental study, which was expected to provide clarity on the topic.
On June 27, TxDOT released its draft environmental impact statement, or EIS—a document that models what would happen if the Central Texas Regional Mobility Authority built the road.
Given the choice between doing nothing and building SH 45 SW, TxDOT prefers building the road to improve system connectivity and travel times, according to the draft EIS.
Carlos Swonke, director of TxDOT's Environmental Affairs Division, said SH 45 SW could be built with a negligible effect on the Edwards Aquifer.
"Our team is doing everything we can to protect water quality and Flint Ridge Cave," TxDOT spokeswoman Kelli Reyna said.
TxDOT and the Mobility Authority partnered with the city of Austin, the Barton Springs/Edwards Aquifer Conservation District, and Travis and Hays counties, among others, on the EIS.
The Capital Area Metropolitan Planning Organization estimates SH 45 SW will cost $100 million to build. Travis and Hays counties, the Mobility Authority and a CAMPO grant will fund the project.
Karsts
TxDOT studied a roughly 5,327-acre area to gauge the potential environmental effects of SH 45 SW.
Roughly 85 percent of the study area lies within the recharge area of the Edwards Aquifer.
The region is home to karsts, or geological passageways in which groundwater can flow and recharge the aquifer.
"Karst landscapes have unique hydrogeology that results in aquifers that are highly productive but vulnerable to contamination," the draft EIS states.
Geologists identified 21 potentially sensitive features that would need changes prior to or during construction. The project would directly affect the openings of seven karst features, four of which were deemed potentially sensitive.
"These seven karst features would require some action prior to or during construction to prevent impacts to water quality," the draft EIS states. Actions may include adding berms—embankments used to divert water—near the road or backfilling karsts to prevent potential contamination of the aquifer.
"The proposed project would include [best management practices] that would collect and treat runoff prior to discharging it off-site," the draft EIS states.
Road designers could use mulch logs, rock filter dams, silt fences and water quality ponds to reduce pollution.
The draft EIS states that road designers may also use suggestions, such as porous pavement, grassy swales and vegetative filters from the Mobility Authority's 2011 Green Mobility Challenge.
The draft EIS states a goal of removing at least 90 percent of total suspended solids—particles of pollution that will not pass through a filter—in the recharge zone of the aquifer.
"Although the proposed project would add new impervious cover over the recharge zone, as proposed, stormwater generated from the road would be treated through water-quality ponds and then released over time to recharge back into the aquifer," the draft EIS states.
Flint Ridge Cave is the fifth-largest and second-deepest cave in Travis County. It is a significant recharge feature and has a ground-level entrance 150 feet away from the state-owned right of way of SH 45 SW.
Encroachment on the drainage basin associated with Flint Ridge Cave could result in a decrease in recharge water volume, resulting in potential drying of the cave environment as well as impacts to aquifer-dependent species. That, in turn, would reduce the amount of recharge to the Edwards Aquifer, the draft EIS states.
Under the current design, no roadway runoff is expected to enter the cave.
Builders could install a berm to channel roadway runoff to water-quality ponds and a clay liner to prevent stormwater runoff from reaching the cave through the soil.
To make up for shrinking the cave's catchment basin, builders could reroute non-roadway runoff into the cave's surface drainage area.
Swonke said the design features proposed for SH 45 SW would reduce pollution to below naturally occurring levels.
TxDOT also studied whether SH 45 SW would affect any threatened or endangered species.
There have been no sightings of the endangered golden-cheeked warbler in the state-owned right of way, according to the draft EIS.
SH 45 SW has the potential to affect several threatened or endangered species that typically live in karsts, but none of the species have been known to live in the karsts that are in the project's right of way.
A potential habitat for the Texas horned lizard was found in the study area, but not in the right of way.
There is no known habitat in the right of way for two endangered salamander species, the draft EIS states.
TxDOT and the Mobility Authority will host a public comment forum at 5 p.m. July 29 at Bowie High School, 4103 Slaughter Lane. Read the full report at www.sh45sw.com
