The Boerne Star recently printed a letter to the editor in which the author discussed the findings of a Trinity Aquifer Study in Kendall County by Wet Rock Groundwater Services.
“According to the report, the average recharge to the aquifer is 132,000 acre-feet per year of which CCGCD permits less than 5,000 acre-feet.”
The study did report the recharge figure of 132,000 acre feet per year. However, this was an average based on precipitation recorded through years 1940 to 2007.
Because droughts are common in the Hill Country and vary in frequency, duration, and lack of rainfall, water plans incorporate the worst-case scenario - a drought of record. Based on measured precipitation for the last 100 years, the drought of record for the Hill Country occurred between 1950 and 1956.
The study noted the average annual recharge recorded for this seven year period was 15,482 acre feet. In the last three years of the drought, 1954-1956, the average recharge was 3,139 acre feet.
Although, this drought is considered the gold standard for planning, a 2006 University of Arkansas study of tree rings indicates there have been droughts far worse. Droughts of the last half of the 16th century certainly exceeded the 1950s drought in duration. Because of the massive increases in population s similar one probably would have a greater impact on Texas if it happened again.
Coincidentally, given the rainfall to date, we are experiencing drought of record conditions today. Until the rains of mid-August, we had only 10.07 inches since October of 2007. Our average rainfall for that period from 1893 to date is 27.46 inches.
Furthermore, these recharge potentials are not to be confused with “recoverable” groundwater. All groundwater is not recoverable. Some is lost to spring flow, some is used by plants while the water is still near the surface, and some is almost permanently retained within the rock itself.
The Wet Rock Study was commissioned by the District. The goals of this study were to determine if the Trinity Aquifer Groundwater Availability Model (GAM) overestimates, underestimates or accurately estimates the groundwater resources of the District based on a comparison with real data.
This study was considered necessary because in the near future, the Texas Water Development Board (TWDB) will use the Trinity Aquifer GAM to assign the amount of groundwater the District will be tasked to manage.
This is referred to as the Managed Available Groundwater or MAG. This MAG could be larger than the roughly 3,800 acre feet the District presently has granted permits for. Until that number is determined, permits should be issued as conservatively as possible.
Recently, you may have read or heard about a water availability study commissioned by the Cow Creek Groundwater Conservation District. The goals of this study (Wet Rock Groundwater Services) were to determine if the Trinity Aquifer Groundwater Availability Model (GAM) overestimates, underestimates or accurately estimates the groundwater resources of the District based on a comparison with real data.
Once this figure is approved, the model will determine the available groundwater of this district. It will be known as Managed Available Groundwater or MAG.
When the process is complete, this district, along with 90 others statewide, must issue permits to the full amount of the MAG.
It is important to note that though all wells must be registered, not all wells are required to have a permit, specifically, an operating permit. Wells used for domestic or livestock purposes are generally exempt from the permit process.
In order to make sure everyone in Kendall County will have access to groundwater in the future, the district will consider domestic exempt wells in the total MAG, something not included in either modeling or the study we have been talking about. [Editors Note: The Trinity Aquifer GAM, TWDB Report 353, September 2000, categorized these wells as unreported domestic. Through analysis of records of the USGS, TCEQ and TWDB, an estimated and predictive demand of groundwater throughout the study area was established. The Wet Rock Study noted much of the groundwater production in Kendall County is under exempt permits. These unmetered wells make it difficult to quantify the total amount of groundwater produced annually].
The exempt wells are estimated to account for 2,500 acre feet. When counted, this demand significantly impacts groundwater availability considering the 3,800 acre feet currently permitted.
Prior to introduction of the MAG concept, Groundwater Conservation Districts either used state-supplied estimates of available groundwater that could be permitted from Regional Water Planning Groups or proposed their own estimates based on independent studies. This autonomy has been replaced by regionalization through recent legislative action.
This district is one of six others within the regional framework of Groundwater Management Area (GMA)-9. Through a process of consensus, all Districts are expected to agree to a Desired Future Condition (DFC).
By TWDB definition: “Desired future conditions are the desired, quantified conditions of groundwater resources (such as water levels, water quality, spring flows or volumes) at a specified time or times in the future or in perpetuity.”
A DFC could be a 25 foot drawdown of the Trinity Aquifer across GMA-9 in 50 years. It could be 33 feet of drawdown in the year 2050. It could just as well be zero.
In any event, this will be determined by consensus. Once agreed to, the DFC will be inserted into the Trinity Aquifer GAM to determine the MAG.
I must reiterate that once approved by the TWDB, Districts will be obligated to permit to the full MAG. It is crucial to understand that the model has limitations and must be evaluated based on all contributing factors used to construct the model.
Just like the model, it is imperative the study recently released by Wet Rock be discussed and analyzed in its full context using factual information.
Meetings are being held to determine the DFC and final MAG, for GMA-9. It is imperative we maintain a conservative approach in order to manage the groundwater for all who depend on this resource within Kendall County.
These facts were taken from the numerous sources used by Cow Creek Groundwater Conservation District and readily available to the public. This information is available on-line or in print at the district office, including the Wet Rock Study posted on the District Web site.
Directors and staff are always available to answer any questions. Additionally, much can be learned about our groundwater resources by attending any of the district meetings.
These are the best ways to learn the truth about water.
Milan J. Michalec is a retired U.S. Air Force veteran who lives near Bergheim in Kendall County. He is serving his second term as a director on the Cow Creek Groundwater Conservation District board. He is a Texas Master Naturalist and member of the Alamo Area chapter of Texas Master Naturalists.
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