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Carrizo-Wilcox Aquifer

The Carrizo-Wilcox Aquifer extends from the Rio Grande in south Texas into parts of Arkansas and Louisiana, supplying water to more than 60 Texas counties. It is one of Texas’ greatest water assets.

The Carrizo-Wilcox is composed mainly of hydraulically connected sands, and it also contains layers of gravel, silt, clay, and lignite deposited during the Tertiary Period. The thickness of the sands can reach 3,000 feet, and the total Aquifer thickness can reach 10,000 feet.

The Carrizo Sand and Wilcox Group outcrop along a narrow band that lies parallel to the Gulf Coast and dips beneath the land surface toward the coast, except in the East Texas structural basin where a trough has formed. The Aquifer is recharged with water from rainfall or from streams that cross the outcrop and lose a portion of their flow to the underlying sands.

(click on map for larger view)

Because of its large size, the Carrizo-Wilcox is broken down into three regions for modeling and planning purposes: Northern, Central, and Southern.

The Northern region of the Aquifer receives the majority of its water from the Brazos, Trinity, Neches, Sabine, and Red River basins. The Central region receives water mainly from the Brazos, Trinity, and Colorado River basins, while the Southern region receives the majority of its water from the Rio Grande, Nueces, San Antonio, Guadalupe, Colorado, and Lavaca River basins.

Groundwater in the Carrizo-Wilcox exists under both water-table and artesian conditions. Water-table conditions usually occur in the outcrop areas, and artesian conditions occur where the aquifer is overlain by confining beds with lower hydraulic conductivity rates. Well yields are usually 500 gal/min, but some may reach 3,000 gal/min downdip where the aquifer is under artesian conditions (Thorkildsen and Price, 1991).

The groundwater in the Carrizo-Wilcox Aquifer is naturally fresh to slightly saline in some places. The chemical quality declines with depth. The deeper waters have higher temperatures and have been under greater pressures, which have led to greater mineralization. In some places it is high in iron that was dissolved from rocks and soils (Thorkildsen and Price, 1991). Flouride and chloride are also present as natural chemicals that dissolved from rocks and soil, and chloride can also be found in the salty water deep water (Follett, 1974). Hydrogen sulfide and methane may be present in some areas (Thorkildsen and Price, 1991). Unlike Edwards water, Carrizo water usually requires treatment, especially to be made compatible with Edwards supplies when mixed in a distribution system.

For purposes of fresh water supply, the Carrizo and Simsboro Formations are the most important layers because they contain more permeable and thicker sands. The Calvert Bluff and Hooper Formations are made of clay, silt, sand, and lignite mixtures; they generally have a low vertical permeability, which makes them act as leaky aquitards that confine fluid pressures in the Carrizo and Simsboro and restrict groundwater movement between the layers (Dutton et al., 2003).

The Lower Wilcox contains slightly saline water that has been called “one of the best potential sources for brackish water in Texas” by the Texas Water Development Board. The San Antonio Water System is currently constructing a facility that will be the largest inland desalination plant in the country when finished in 2016 (see the Desalination page).

In addition to desalination of water from the Lower Wilcox, there are several projects that have been completed or are under development to diversify San Antonio’s water supply and reduce the city’s reliance on the Edwards Aquifer. These are the Gonzales Project and the Vista Ridge Project.

Gonzales Leases

On August 20, 2002 the Board of the San Antonio Water System approved the lease of 4,635 acres in central Gonzales county over a productive part of the Carrizo Aquifer.  The utility planned to bring the water source online in 2007 if an initial drilling program determined the project was feasible.  Two more leases were planned totaling another 10,400 acres, and total production from the three leases could total about 20,000 acre-feet per year.  Landowners would be paid $62.50 per acre-foot.  The total project cost was estimated to be about $102 million, including the land and water leases, construction of a wellfield, treatment facilities, and a 58 mile long pipeline to bring the water to San Antonio (1).

The cities of Seguin and Schertz also leased land in Gonzales county to extract a similar volume of water, and the Bexar Metropolitan Water District leased land and water rights on the border of Gonzales and Guadalupe counties for water production.

In 2003, some area residents began to become concerned about the project when different groundwater models predicted very different impacts.  The Texas Water Development Board prepared separate models of the southern and central Carrizo, but they overlapped in Gonzales county, and one model predicted there was about four times as much water available as the other.  The Gonzales County Groundwater District adopted the more conservative model, but SAWS said its own modeling and field tests showed there is plenty of water available.  Since SAWS needs permits from the District, how the agencies resolved the disagreement had potential to impact the future of the project (2).

By late 2005, with SAWS preparing to drill wells and start pipeline construction, there were rising concerns among area citizens about the impact the project will have on their own wells.  SAWS stressed that it has a strong commitment to mitigation of any impacts, while District general manager Barry Miller said the permits that SAWS requires "do not fit the district's certified management plan."

In April of 2006 SAWS scaled back the project, eliminating plans to take groundwater from eastern Gonzales county (3)

In October of 2008 the Guadalupe-Blanco River Authority announced the filing of permit applications for a new water project involving the Carrizo. The project would provide up to 30,000 acre-feet of water per year to Caldwell and Hays counties. The plans include drawing water from the Guadalupe River near Gonzales, along with a Carrizo Aquifer wellfield and an off-channel storage reservoir on a tributary of the Guadalupe River. The permit application requests that during wet years, GBRA be allowed to divert all 30,000 acre-feet from the Guadalupe. During dry years, the Carrizo wellfield and/or the off-channel reservoir would supplement available Guadalupe supplies. GBRA General Manager Bill West said he hoped the project could be online in five to seven years (4).

In July of 2010, the board of the Gonzales County Underground Water Conservation District voted 3-2 to approve SAWS’ permit application to pump 11,687 acre-feet per year from the Carrizo. The permit is for 30 years but has to be renewed every five (5).

SAWS then completed negotiations to rent pipeline capacity from the Schertz-Seguin Local Government Corporation (SSLGC), which built a pipeline from the Carrizo to supply water to those two towns. In February of 2011, SAWS and the SSLGC signed a contract. In addition to the 11,687 acre-feet for which SAWS received a permit, the contract provides SAWS an option to purchase up to 5,000 acre-feet per year of surplus water not used by the cities of Schertz and Seguin (6).

On Nov. 13, 2013, San Antonio received its first delivery of Carrizo water from the SSLGC, a flow of about 4.5 million gallons. Water is integrated into the SAWS system on the northeast side of town. Construction of new wells on SAWS' leased properties was well under way, as well as a major expansion of SSLGC's treatment facility.

New Carrizo well

One of SAWS' new Carrizo Aquifer wells nearing completion in January of 2014. These wells are part of SAWS efforts to expand and diversity its water supplies.

Carrizo treatment units

As Carrizo water requires treatment, SSLGC's facilities were expanded to accommodate the increased volume from SAWS wells.

Greensand filters

Part of the treatment process involves filtration using Greensand, a product made by the Inversand company for removal of iron, manganese, arsenic, radium and hydrogen sulfide in municipal and industrial treatment applications. Here, bags of Greensand await installation in the new filtration unit in January of 2014.

The Vista Ridge Project

In January of 2011, SAWS issued a formal request for proposals for new water supply projects that would provide an alternative water source and help diversify the city’s long-term water supplies (7). The objective was to identify projects by which private sector suppliers could provide 20,000 acre-feet per year to San Antonio by 2020, and 60,000 acre-feet by 2060. Another objective was to shift all risk to a private developer; SAWS was seeking a turnkey solution in which a developer would build a project and deliver water to a local SAWS pump station.

There were nine proposals received and in 2013, three were still under consideration. SAWS also broadened the scope of the deal by asking finalists to rework their proposals to supply up to 50,000 acre-feet instead of 20,000, and it moved the start date up to 2018 from 2020 (8). But significant public oppositon emerged against two of them, and SAWS said it would listen to the concerns of opponents (9), (10).

The only proposal with no significant opposition was that of the Vista Ridge consortium to bring Carrizo Aquifer water from east of Austin. The Vista Ridge consortium is is composed of Austin-based Blue Water, which has obtained long-term pumping and transfer permits, and Abengoa, a Spanish-based firm that will build the pipeline. Their proposal was ranked the highest by SAWS staff, but there were several aspects of the proposal that SAWS found unsatisfactory. Most importantly, it could only guarantee costs and not water. SAWS CEO Robert Puente said “The highest ranked proposal was unwilling to assume the risk of water being cut off by the groundwater district that regulates the supply. We are unwilling to ask our ratepayers to absorb the cost of a project with potentially no water.”

Other concerns with the Vista Ridge proposal were a $5 million annual “reservation fee”, and annual 2% price escalations.

In light of all this, SAWS announced it would recommend to its Board of Trustees that it accept none of the proposals and instead focus on an expansion of its brackish water desalination plans. Desalination could be phased in as necessary, so that investment could be matched to need (11).

Not everyone was immediately sold on the idea of expanding desalination instead of accepting one of the private sector proposals offered for new supplies. Mayor Julian Castro said he was open to support desalination as a way for San Antonio to "control our own destiny", but he also wanted to keep the door open to purchase of other supplies (12). Long-time water advocate Weir Labatt also said he supported desalination but feared the city might fumble yet another chance to buy water from outside the region. "San Antonio had had a history of failed attempts to secure additional water," he said. "What I hope is this is not another chapter in that same story. I'm afraid it might be." (13)

The private firm asked SAWS to reconsider its decision, saying it was not provided “an opportunity to fully explore solutions” to SAWS concerns about its proposal (14).

The business community responded to SAWS announcement by releasing a study that spelled out dire economic consequences if only a small shortfall of water were to occur (see study). SAWS countered by pointing out that water for business and industry would never be cut because it has the supplies to support economic growth. In a statement SAWS said "The only cuts we require of our customers is for lawn and landscape irrigation." (15)

In any case, SAWS Board voted to continue discussions with Vista Ridge, but also defended the staff recommendation. Chairman Berto Guerra said "While I appreciate comments from various members of the public, I do not want to commit our ratepayers to $85 million per year for 30 years for a project that may or may not deliver on its promise. We stand together as a Board. We stand behind our Mayor. We stand behind Robert Puente." (16)

By mid-June of 2014, SAWS was making progress on re-negotiating the proposal. President and CEO Robert Puente said “the major hurdles and objections to the original proposal from Vista Ridge are being overcome, and we can now take the next step toward securing the largest non-Edwards supply in our city’s history.” (17). Vista Ridge agreed to assume all risks with the project, and also agreed to waive the $5 million reservation fee and automatic annual price increases (18).

On July 1, 2014, the SAWS Board formally approved the proposal and appointed a negotiating team to work out the details of a long-term contract for Board and City Council approval in the fall (19).

SAWS CEO Robert Puente said "This project is a game-changer for San Antonio, helping us meet a diverse and growing demand for water for decades to come. Purchasing this quantity of water is one of the most significant decisions our community will make. It will require a 30-year commitment of annual payments, but it will provide the security of knowing our economic future and our quality of life will not be held back because of a lack of water (20)."

In a move to promote transparency and invite ratepayer scrutiny, SAWS decided to conduct negotiations in public. A series of seven negotiation sessions were attended by news media, elected officials, environmental groups, and the general public. Along the way, SAWS conducted 61 separate community presentations, meetings, and tours.

By mid-September, SAWS had wrapped up talk with Vista Ridge and secured much more favorable contract terms. These included a fixed long-term price, payment only for water actually delivered, elimination of annual reservation fees, a cap on the interest rate that may be applied when Vista Ridge secures its financing, ownership of the pipeline and facilities at the end of the 30-year contract, and a right of first refusal on water purchases after 30 years. The SAWS Board of Trustees approved the contract on September 29 (21), and a vote by City Council may be scheduled for late October. SAWS also began discussions with cities and water providers that may be interested in purchasing some of the water on an interim basis, until it is needed in San Antonio.

Meanwhile, some opposition to the project emerged, but not from the hundreds of Burleson county residents who own the water. SAWS Trustee Reed Williams noted "It's their water. It's their right to sell it, and it's their right to control it (22)."

Opponents seemed to be mainly people from adjacent counties who fear the impact of the project on their own ability to produce Carrizo water. The League of Independent Voters of Texas began assisting their efforts to organize and enlist lawyers to speak against the project.

The Greater Edwards Aquifer Alliance also emerged in oppositon - in an editorial piece GEAA President Annalisa Peace urged the city not to "rush to judgment" on the project and postpone a decision until a new City Council is installed in June of 2015 (23). In an email to supporters and in online materials, GEAA emphasized the main issue for them is the development that new water supplies would bring. SAWS insisted that it would remain vigilant in Edwards Aquifer protection, and that having an abundant water supply would not cause it to abandon its world-famous culture of conservation.

In anticipation of a City Council vote on October 30, a public hearing was scheduled for October 8 at 6:00 pm in council chambers.

At the hearing about 100 people signed up to speak, and opinions were about evenly divided, except that most who spoke in favor were locals and most in opposition were from elsewhere.

Speaking in favor were residents, small business owners, representatives from the Bexar County Medical Society, local banks, the Responsible Growth Alliance, several Chambers of Commerce and builders associations, the San Antonio River Authority, and community organizations.

Speaking against the project were legal representatives of the League of Independent Voters, the Sierra Club, the Save Our Springs Alliance, property owners in Lee and Burleson counties, and the Greater Edwards Aquifer Alliance. Objections focused mainly on the impacts that growth and development will bring, although water attorney Amy Hardberger focused her comments mainly on financial questions.

Speaking in favor of the project, San Antonio River Authority General Manager Suzanne Scott noted the environmental benefits it could bring - it could restore longer periods of natural springflow in Bexar county and would make SAWS' commitment to release recycled water for environmental flows more certain.

Several speakers noted an irony that is evident in the opposition from environmental groups - in the 1990s they sued San Antonio to force the city to diversity its water supplies, and now they seem opposed to that diversification.

For readers who would like to contrast some different viewpoints, here are two editorial pieces by Amy Hardberger and Rep. Lyle Larson:

Water Partnership Should Become Model for Texas, by Lyle Larson.

Vista Ridge Project Creates More Questions than Answers, by Amy Hardberger.

When San Antonio's City Council met to vote on the project on October 30, advocates and opponents again turned out for a nearly four hour discussion that included presentations from city staff, SAWS, and remarks from each councilmember.

The City's Chief Financial Officer Ben Gorzell said SAWS had "done their homework" in structuring a deal that his staff strongly supported.

SAWS President and CEO Robert Puente reiterated that SAWS three core principles are protection of the Edwards Aquifer, an unwavering commitment to conservation, and lifeline rates for low water users.

Mayor Ivy Taylor noted that Vista Ridge goes further than water and touches on larger issues such as balancing prosperity with environmental protection, and that both opponents and proponents have something to offer in the debate. She said the city must use the "expertise and convictions" of all "to create and adopt a real, regional comprehensive plan that mandates more efficient growth, protects the air and water quality and offers a better environment for humans and endangered species (24)."

In the end, the project received unanimous council support.

The League of Independent Voters promised it would be back and would continue to try and unravel the project, pointing to a 30-month time period in which San Antonio can still walk away from the deal (25).

Materials used to prepare this section:

Deeds, N., Kelley, V., Fryar, D., Jones, T., Whallon, A.J., and Dean, K.E. (2003). Groundwater availability model for the Southern Carrizo-Wilcox Aquifer. Final report, prepared for Texas Water Development Board. 

Dutton, A.R., Harden, B., Nicot, J.P., O’Rourke, D., and Tinker, S.W. (2003). Groundwater availability model for the central part of the Carrizo-Wilcox Aquifer in Texas. Final report, prepared for Texas Water Development Board. 

Follett, C.R. 1974. Ground-water resources of Brazos and Burleson Counties, Texas. Report prepared by United States Geological Survey for the Texas Water Devlopment Board, USGS Report 185.

Fryar, D., Senger, R., Deeds, N., Pickens, J., Jones, T., Whallon, A.J., and Dean, K.E. (2003). Groundwater availability model for the Northern Carrizo-Wilcox Aquifer. Final report, prepared for Texas Water Development Board.

Mace, R.E, Smyth, R.C., Xu, L., and Liang, J. (1999). Transmissivity, hydraulic conductivity, and storativity of the Carrizo-Wilcox Aquifer in Texas. Austin: Bureau of Economic Geology.

Thorkildsen, D. and Price, R.D. (1991). Ground-water resources of the Carrizo-Wilcox Aquifer in the Central Texas Region. Austin: Texas Water Development Board, Report #332.

(1) "SAWS eyes Gonzales leases" San Antonio Express-News, August 20, 2002.
(2) "SAWS making waves in Smiley" San Antonio Express-News, December 31, 2003.
(3) "SAWS cuts back Carrizo project" San Antonio Express-News, April 5, 2006.
(4) "Guadalupe-Blanco River Authority project would help Caldwell, Hays" San Antonio Express-News, October 25, 2008.
(5) "SAWS will tap into Carrizo Aquifer" San Antonio Express-News, July 14, 2010.
(6) "SAWS signs Carrizo Aquifer deal" San Antonio Express-News, February 2, 2011.
(7) "SAWS accepting proposals on long term water project" San Antonio Express-News, January 13, 2011.
(8) "SAWS is shooting for bigger water deal " San Antonio Express-News, September 1, 2013.
(9) "SAWS debate starting to boil " San Antonio Express-News, October 23, 2013.
(10) "West Texas water proposal critics will have SAWS ear, says CEO" San Antonio Express-News, January 16, 2014.
(11) "SAWS staff urging board to reject private proposals for new water, February 7, 2014.
(12) "Mayor not sold on brackish water" San Antonio Express-News, February 11, 2014.
(13) "Desalination water option prompts concerns" San Antonio Express-News, February 16, 2014.
(14) "SAWS urged to reconsider plan" San Antonio Express-News, February 9, 2014.
(15) "SAWS responds to dire Chamber of Commerce report" Ticket 360, March 3, 2014.
(16) "Deal on brackish water plant gets OK" San Antonio Express-News, March 5, 2014.
(17) "SAWS officials make progress on long-term water proposal" San Antonio Business Journal, June 19, 2014.
(18) "SAWS says that would-be supplier is willing to assume all risks" San Antonio Express-News, June 18, 2014.
(19) "SAWS selects proposal for largest non-Edwards water deal" La Prensa, July 2, 2014.
(20) "SAWS moves forward on largest-ever non-Edwards supply" San Antonio Water System press release, July 11, 2014.
(21) "SAWS wraps up talks on water pipeline" SAWS WaterMark, September 29, 2014.
(22) "CEO sells project as regional answer" San Antonio Express-News, September 30, 2014.
(23) "Don't allow rush to judgment on pipeline" San Antonio Express-News, October 3, 2014.
(24) "Council OKs water pipeline" San Antonio Express-News, October 31, 2014.
(25) "Thanks San Antonio Council...we have 30 months to bust Vista Ridge!" League of Independent Voters, Staff Writer, October 31, 2014.