Where does the groundwater being pumped from the Simsboro Aquifer come from?

Environmental Stewardship participated in the GMA-12 review of the adopted desired future conditions from 2014-2016 and provided comments on the nine (9) considerations that the GMA are required to evaluate during the review and re-adoption process.   The following are comments provided to GMA-12 on consideration 3.   ES’ comments are based on presentations on GAM runs that were intended to review the hydrological conditions for each aquifer that included water budgets for each aquifer.  Through analysis of these reports ES was able to estimate the sources of groundwater being pumped from the Simsboro aquifer.

CONSIDERATION 3– “Hydrological conditions, including for each aquifer in the management area the total estimated recoverable storage as provided by the executive administrator, and the average annual recharge, inflows, and discharge:”  

ES Initial Comments to GMA-12June 18, 2015

SUMMARY OBSERVATION: The GAM results indicate that the most significant contributors of groundwater for pumping of the Simsboro aquifer are from

1) a reduction in outflows to surface waters, and

2) the flow of groundwater out of other aquifers within the district.

Water Budgets Observations: Environmental Stewardship analyzed the water budgets for the Simsboro aquifer in the five districts and consolidated for the GMA (See Attachment 1) .

The following observations are from the analysis:

a) Outflows to surface waters: Surface water is the single most significant contributor of water for pumping. Outflows to surface waters are modeled to have decreased by a total of 100,000 ac-ft/yr since 1975 with the greatest declines occurring in Post Oak Savannah, Lost Pines, and Mid-East Texas respectively.

b) Storage changes: Storage is the least significant contributor of water for pumping since 1975. Storage increased during the calibration period and decreases during the DFC period but is net neutral for the period. It is misleading to state that most of the groundwater pumped is contributed from storage.

c) Vertical leakage: Vertical leakage from other aquifers into the Simsboro is the second most significant contributor of groundwater for pumping since 1975 (modeled to contribute 83,300 ac-ft/yr) and is the most significant contributor during the DFC period (modeled to contribute 69,800 ac-ft/yr by 2070). Vertical inflow to the Simsboro is most significant in Post Oak Savannah, Brazos Valley, and Lost Pines respectively during the DFC period.

d) Lateral leakage: Lateral flow of groundwater from other districts into the Simsboro in Brazos Valley is significant during the DFC period. Lateral flows out of Lost Pines and Mid-East Texas are the most significant with moderate outflows from Post Oak Savannah.

e) Pumping: By 2070 the annual pumping of the Simsboro aquifer in the GMA is estimated at 244,000 ac-ft per year with the highest pumping in Brazos Valley, Post Oak Savannah, and Lost Pines respectively.

SUMMARY OBSERVATION: The GAM results indicate that the most significant contributors of groundwater for pumping of the Simsboro aquifer are from

1) a reduction in outflows to surface waters, and

2) the flow of groundwater out of other aquifers within the district (without consideration of the limitations noted in items 1 and 2 above).

Considerable technical analysis of existing empirical data and observations need to be undertaken by the technical team in order to provide the GMA-12 districts a better understanding of the implications of these factors as they relate to:

1) the desired future conditions,

2) impacts on the surface water and terrestrial environments, and

3) exempt groundwater wells in aquifers contributing to vertical flows. To a lesser extent the impacts of lateral flows between districts needs to be investigated.

ES Supplementary Comments to GMA-12 – March 22, 2016:

  • Observation from ES June 18, 2015 comments demonstrated that the GAM results indicate that the two most significant contributors of groundwater for pumping of the Simsboro aquifer are from 1) a reduction in outflows to surface waters, and 2) the flow of groundwater out of other aquifers within the districts.
    • ES submits a new GAM analysis by George Rice titled “GAM Predictions of the Effects of Baseline Pumping Plus Proposed Pumping by Vista Ridge, End OP, Forestar, and LCRA” dated March 22, 2016 (Attached). The report examines the effects of pumping on groundwater and surface water in the Lost Pines Groundwater Conservation District (LPGCD), the Post Oak Savannah Groundwater Conservation District (POSGCD), and surrounding counties.
    • The Rice report demonstrates that the GAM predicts:
      • Significant communication between the Simsboro, Hooper, Carrizo and Calvert Bluff aquifers in the Carrizo-Wilcox Group.
      • Significant decrease in outflow from these aquifers to the Colorado River and its tributaries (see Consideration 4).
      • Significant drawdown from anticipated pumping of the Simsboro aquifer in the Simsboro, Hooper Carrizo and Calvert Bluffs aquifers regionally in counties outside GMA-12 (as far away as Gonzales, Lavaca, Colorado, Austin, Grimes, and Walker counties).
      • Baseline plus additional pumping will exceed current and proposed DFCs in the Simsboro Aquifer by 2060 (see Consideration 8).