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Groundwater sampling helps better understand Edwards-Trinity Aquifers

By Amira Van Leeuwen

The Texas Water Development Board (TWDB) and scientists from the Barton Springs Edwards Aquifer Conservation District (BSEACD) are studying water deep underground to further understand how drought and pumping affect the quality and quantity of groundwater that flows between the Edwards-Trinity Aquifer systems.  

About $98,000 financed the study, which paid for drilling, materials and water quality analyses. 

The TWDB provided $25,000 to fund a set of water quality analyses called isotopes. Isotope analyses help hydrologists determine the age of water and where it comes from. 

According to Natalie Ballew, director of the groundwater division, the data from the study will be used by the area’s groundwater conservation districts to better understand how the aquifers communicate with one another and what kinds of flows are happening between the aquifer and formations.

Hays County contributed $58,000 to the study, the Hays Trinity Groundwater Conservation District (HTGCD) $25,000 and the BSEACD about $15,000.

“We’re all trying to understand the Trinity aquifers within our districts and beyond,” BSEACD’s Principal Hydrologist Brian Smith said.

According to Smith, they have already done testing for hydraulic conductivity, which is the number that tells scientists how easy or hard it is for water to move through the aquifers.

Smith said the area around Jacob’s Well has Trinity water flowing through the aquifers from west to east or the southeast, and as a result, the water is flowing through the HTGCD’s area of authority as well as BSEACD’s. 

“We also see that heavy pumping on one side of that political boundary can affect the other side,” Smith said. “So our board of directors can set a policy, as we consider the sustainable yield of the Trinity aquifers, basically how much pumping could be allowed under drought of record conditions without causing unreasonable impacts to the aquifers and to the users of if there are any endangered species that might be involved.”

Smith said one study factor was looking at the springs that could be affected, citing Jacob’s Well. Analyses have shown that heavy pumping within the BSEACD could affect the well. Heavy pumping around the Wimberley area also affects Jacob’s Well.

“Like we’re seeing right now, when you combine drought with heavy pumping locally, sort of long-term drought, long-term pumping from further away can impact Jacob’s Well and other areas,” Smith said. 

Other than springs, they have looked at water levels and impacts on wells and well users. Smith said they don’t want the water levels dropping to the point that well users wouldn’t be able to get water from the wells they rely on. 

The key points within the study were installing two monitor wells near Jacob’s Well.

One of the wells, a Multiport Monitor Well, was installed to help hydrologists and scientists to better understand the complex relationship between different aquifers and hydrologic units within an aquifer. A multiport well can divide up the units discreetly in the subsurface and gives the same measurements as a single well would, but in multiple levels with that single well. The second monitor well installed was a Dual Completion Well, which involves a standard monitor well installation. 

“The data coming out of them looks very good,” Smith said. 

Ballew thinks the data from the study serves multiple purposes.

“It helps the districts understand how to best manage their resources and to balance the impacts from a growing population area who are pumping more groundwater,” Ballew said. “But also, with probably the forecast, we’re gonna have more droughts, so understanding that I think will help the district to make better resources management decisions that will ultimately ensure that there’s enough water for everyone who’s coming into Central Texas.”

Although the study is ongoing, the water districts will continue to collect water quality samples. All data will be made publicly available to assist in the decisions regarding managing significant groundwater resources for the future.

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