SAN ANTONIO – In a letter sent to the mayor and City Council ahead of Thursday’s vote, hydrogeologist Dr. Ronald Green argues the safeguards tied to the Guajolote Ranch project will not protect the Edwards Aquifer the way some officials say they will.
The dispute comes down to one question: Will a wastewater treatment plant required for the development put San Antonio’s drinking water at risk?
Guajolote Ranch is a planned development that will bring roughly 3,000 homes to northwest Bexar County and will require the construction of a wastewater treatment plant.
San Antonio Water System has argued that a natural underground layer protects the Edwards Aquifer, keeping treated wastewater away from where the city gets its drinking water.
But Green — who has studied San Antonio’s karst aquifer system for decades — says that explanation does not match what research has shown underground.
“The old perception of that is that the contributing zone acts as a tin roof and so all the rain and precipitation falls on it,” Green said. “What we’ve seen, with a number of studies and field investigations, is that that’s not how it works. The tin roof is like a leaky tin roof.”
Green says the geology in this area is not a solid barrier — it is porous limestone that allows water to move quickly underground.
“This is all limestone,” Green said.
Green also described the karst terrain as a system where water moves through openings in the rock.
Because the development site sits near areas where water enters the Edwards Aquifer, Green said contaminants could potentially reach public water supply wells in a short time.
“If they’re only 10 or 15 miles from public water supply wells, where this water is introduced into the environment, it can get there in a matter of weeks,” Green said. “And that’s a real concern because anything in that water that’s not good is going to get into the aquifer, and that includes pathogens.”
Green also questioned the basis for the utility’s conclusions.
“I’ve been studying this for about three decades now,” Green said. “I have not seen any recent studies, documentation, or data to support otherwise.”
Following Green’s letter, SAWS sent KSAT a statement saying it has “conducted rigorous reviews of the underground geology, as we have for decades.”
“SAWS also negotiated unprecedented water quality conditions into the service agreement, which will provide additional protections to ensure that our water source is not compromised,” the statement continued. “Water provided to SAWS customers will always be of the highest quality.”
Even though Guajolote Ranch is outside San Antonio city limits, the city still has a stake in the project.
On Thursday, San Antonio City Council is scheduled to vote on a financing model that would help pay for the wastewater treatment plant, a decision that could help move the project forward or become a roadblock for developers.
KSAT Reporter Sarah Acosta has been covering the development at Guajolote Ranch for months. Read more of her coverage: