About 50 feet underground, a machine ate into the white limestone wall, cutting and grinding it into chunks of rock and dust.
The machine, called a roadheader, used an extended boom with a spinning metal head that looked a bit like a spiky plastic dog toy. In the neighborhood of Stone Oak north of Loop 1604, the rock the machine was churning through is part of the Edwards Aquifer, a major underground water source for San Antonio.
The roadheader work is part of a series of projects underway by the San Antonio Water System to help untether San Antonio’s growth from the Edwards Aquifer. SAWS’s Vista Ridge pipeline is set to bring in water from underground aquifers 140 miles away in Burleson and Milam counties.
SAWS is racing to finish the pipeline and other infrastructure before Vista Ridge starts flowing and SAWS becomes contractually obligated to pay for the water it delivers.
“The most critical thing on this is to get everything in place by April 2020 so that we can make sure we meet our deadline,” said Alissa Lockett, SAWS director of Vista Ridge integration, on a Monday tour of Agua Vista Station, the endpoint of Vista Ridge.
The work to build this integration pipeline involves eight projects totaling $165 million in construction costs, Lockett said. As Vista Ridge water flows from north to south through San Antonio, this central pipeline will channel it into existing water mains that deliver water to homes and businesses throughout the central part of the city.
Making that happen involves some ambitious tunneling by contractors with Guy F. Atkinson Construction, many fresh off a similar tunneling job in Atlanta.
It all starts with the roadheader and the work necessary to clear debris out of the tunnel and make sure the tunnel doesn’t cave in. After the roadheader creates a shaft 125 feet long, crews will lower in a cylindrical tunnel-boring machine with a head full of disc-shaped metal bits. That machine will bore a roughly 4,700-foot tunnel 8 feet in diameter from a point near Las Lomas Elementary School to Sonterra Boulevard.
From there, a trench to be cut along Sigma Road will connect that tunnel to another 8-foot-diameter tunnel that will stretch 3,600 feet west-to-east from Cornerstone Church at Loop 1604 and Stone Oak Parkway to Sigma Road. Atkinson crews are using two tunnel-boring machines to drill the tunnels at around the same time.
The tunnels are all part of work the utility is doing to add new pipelines and rehabilitating existing infrastructure in the central spine of its system. This pipeline, which SAWS officials call the Central Water Integration Pipeline, will stretch from Stone Oak to a pump station near Alamo Quarry Market.
The cost to build the Central Water Integration Pipeline isn’t included in the estimated $2.8 billion that San Antonio Water System customers will pay the consortium of private companies building Vista Ridge over 30 years. SAWS expects the pipeline to deliver up to 50,000 acre-feet per year of water, at a cost of approximately $2,000 per acre-foot, the most expensive water in SAWS’ portfolio.
While opponents of Vista Ridge have decried it as a costly, unnecessary way for San Antonio to avoid more serious water conservation, SAWS and the project’s supporters say the Vista Ridge will lock San Antonio into a firm water supply that will help the city grow over generations.
SAWS currently gets most of its water from the Edwards Aquifer, which also supplies other cities and farmers in the region and connects to the springs that form the headwaters of the Comal and San Marcos rivers in New Braunfels and San Marcos, respectively.
In the 1990s, an Endangered Species Act lawsuit over sensitive species that depend on aquifer-fed springs eventually led to pumping limits on the Edwards Aquifer. That in turn led SAWS to begin looking for new ways to tap other water sources in the region.
In 2014, it signed a contract with a consortium of private companies, led by Spanish conglomerate Abengoa, to buy water from Vista Ridge if the companies successfully built the pipeline. After Abengoa began financially imploding in late 2015, Kansas City, Missouri-based Garney Construction took over a controlling stake in the Vista Ridge project in 2016.
Once complete, SAWS plans to make payments on the water for 30 years before taking ownership of the pipeline in 2050.
SAWS customers will see their bills rise next year to cover the cost of Vista Ridge water; the utility got City Council approval in 2015 for a nearly 10 percent bill increase in 2020. SAWS officials have said they plan to seek a little less of an increase than that but have not specified how much.