CONSIDERING THE HYDROGEOLOGIC REASONABLENESS OF DESIRED FUTURE CONDITIONS OF TEXAS AQUIFERS

Groundwater in Texas is managed by groundwater conservation districts through management goals called “desired future conditions.” A desired future condition (DFC) is the desired, quantified condition of groundwater resources for an aquifer within one of sixteen regional groundwater management areas (GMA) at a specified future time or times. The DFC can be appealed to the Texas Water Development Board (TWDB) on the basis that it is not reasonable. But the law does not define “reasonable” nor does it provide guidelines for the TWDB to determine whether or not a DFC is reasonable.

The TWDB reviewed nine petitions challenging the reasonableness of six DFCs in seven GMAs. To determine if a DFC was reasonable the TWDB considered seven criteria, three of which center on hydrogeologic issues: DFCs are physically achievable considering groundwater use, impacts to spring flow or other interaction between groundwater and surface water, and reasonable and prudent development of the state’s groundwater resources.

Specific hydrogeologic issues raised included: adopting an average drawdown for multiple aquifers; adopting an average drawdown that was ambiguous; not considering drought conditions; using a groundwater flow model that was not sufficiently complex; and inaccurate inclusion of existing or permitted pumping. Evaluating the reasonableness of the DFCs involved hydrogeologic reviews of local and regional aquifer conditions, water level trends and groundwater usage projections, and simulation of planned groundwater development scenarios.

Only one DFC was found to be unreasonable. Multiple groups in one GMA had challenged the reasonableness of the DFC for the Edwards part of the Edwards-Trinity (Plateau) Aquifer. The TWDB Board found that the DFC, which allowed "for no net increase in average drawdown” was unreasonable because projected growth in production from wells exempt from regulation would increase the drawdown beyond "current conditions." The DFC was unreasonable because it was not physically achievable. The TWDB Board recommended that it be revised to incorporate the probable growth of exempt pumping.