Water models called ‘faulty’

Published August 19, 2009

The process for determining groundwater availability is coming under fire by the Plateau Water Planning Group (Region J), with the support of other water management groups such as Headwaters Groundwaters Conservation District and the Upper Guadalupe River Authority.

On Tuesday, the PWPG board overwhelmingly voted to appeal to the Texas Water Development Board regarding what are deemed “desired future conditions” based on “faulty” models for the Edwards-Trinity Aquifer, established by Ground Management Area 9.

Desired future conditions are defined as the desired, quantified conditions of groundwater resources, such as water levels, water quality, spring flows and volumes at a specified time or times in the future or in perpetuity.

Models are used to calculate “managed available groundwater” values, which are used for regional water plans, groundwater management plans and permitting.

PWPG Chairman Jonathan Letz said the models never were intended to predict groundwater availability in specific areas.

He said the intent of the appeal process, ultimately, is to bring the matter before the Texas Legislature. But before that can happen, a petition first must be filed with the TWDB.

“I think this is a really important issue,” Letz said. “Once these numbers get published, it will have an impact on the public. To use these models to set DFC is a problem.”

Reasons for appeal

The PWPG contends the TWDB developed two models that can be used for groundwater availability for the Edwards Groups of the Edwards-Trinity (Plateau) Aquifer — the Hill Country Trinity Model and the Edwards-Trinity Model.

However, GMA9 used only one model, the HCTM, for determining the DFC and managed available groundwater.

PWPG board members say both models, along with additional scientific data, should be used to determine DFC.

Letz said 30 percent of the Edwards-Trinity Aquifer within Kerr County is not included in the HCTM model — a point disputed by GMA 9 representative Mary Ellen Summerlin.

Also, PWPG contends the Edwards-Trinity Aquifer extends beyond the three counties within GMA9. Therefore the DFC set by GMA7, which includes counties that impact the aquifer, should have been considered.

The PWPG also is concerned that the available groundwater for Bandera and Kerr counties, as set by the 2006 State Water Plan, was not considered in setting any DFC for the Edwards-Trinity Aquifer.

Evidence of such can be found in the 2005 PWPG study and report, “Spring Flow Contribution to the Headwaters of the Guadalupe River in Western Kerr County,” Letz said.

The study “clearly shows” the variability of the aquifer as determined by the variability of its spring flow, he said.

While Letz said the Hill Country Trinity Model had not been updated since 2003, GMA9 representatives said a new model is due out within a month or so.

The chairman also said a DFC set solely by aquifer drawdown in an area dominated by exempt wells is not reasonable because it cannot be regulated or enforced.

Another concern pertained to a GMA9 joint planning meeting that took place Aug. 29, 2008, where 22 people asked GMA9 to refrain from setting the DFC at that time. It was noted the deadline to set the DFC was about 18 months away and new data could have been added to the models, including information pertaining to “the drought of record” in August 1956.

The PWPG also contends the aquifer was extensively studied for the 2001 and 2006 State Water Plan, but GMA9 did not reconcile the difference between the DFC it established and regional water planning. The 2006 study was the first to include an evaluation on the relationship between surface water, spring flow and groundwater as they pertained to the Edwards-Trinity Aquifer.

Lastly, the TWDB rules and House Bill 1763 require a DFC to be “quantified and enforced” by a groundwater district. But Letz said DFC set for GMA9 allows for “no net increase drawdown.”

He noted a study has shown the aquifer level varies substantially through Kerr and Bandera counties.

Furthermore, Letz said it’s not possible to adequately monitor the aquifer in two counties, considering there’s only one monitor well.

Specifics, such as when, where and how to monitor aquifer levels, also were not determined, he said.

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