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The Edwards Aquifer is one of the most prolific in the world. Located on the eastern edge of the Edwards Plateau in the U.S. state of Texas, it is the source of drinking water for two million people, and is the primary water supply for agriculture and industry in the aquifer's region. Additionally, the Edwards Aquifer feeds the Comal River and San Marcos Springs, provides springflow for recreational and downstream uses in the Nueces River, San Antonio, Guadalupe, and San Marcos river basins, and is home to several unique and endangered species.
The total area of the aquifer forms roughly the shape of a slight upward curve and approximately measures east to west at its furthermost boundaries and north to south at its widest section.Eeason, Sarah. "EAA Subchapter 713 Regulated Zones". ArcGIS. ESRI. Retrieved 17 October 2015. The aquifer is geographically divided into four distinct regions: the total drainage area, recharge zone, artesian zone, and saline zone. These zones run east to west, with the drainage area forming the northernmost portion of the aquifer and the saline zone forming the southernmost portion. The artesian zone intersects the saline zone to the south and west at the fresh water - saline water boundary (FW-SW).
The aquifer's recharge zone, Texas Commission on Environmental Quality where surface water enters the aquifer, follows the Balcones Fault line, from Brackettville (roughly along U.S. Highway 90), through San Antonio, and north to Austin along but a few miles west of Interstate 35. On certain stretches of highway in Austin and San Antonio, signs indicate that the driver is entering or leaving the recharge zone, as the zone's easternmost edge sits beneath heavy urban and suburban development.
Its drainage area, where water is transported near the surface to the recharge zone, extends about north of the recharge zone at the west end, and tapers to end at a point in the east.
The Artesian aquifer, San Antonio Water System where water springs from wells naturally due to the higher elevation of the recharge zone, extends south on the west end to only a few miles south on the east end. Across the eastern half of the aquifer, the recharge and artesian zones occupy common area.
The Maverick Basin portion of the Edwards Aquifer consists of the West Nueces, McKnight, and Salmon Peak Formations. The Devils River Trend unit of the Edwards Aquifer is composed mostly of Devils River Limestone with a thickness of approximately . The third unit of the Edwards Aquifer, the San Marco Platform, consists of the Kainer, Person, and Georgetown Formations.
In the south, the Edwards Aquifer dips beneath the lowland plains of the gulf coast. This area south of the recharge zone is referred to as the Artesian Zone, where the water is held under pressure by low permeability layers, and can flow to the surface without the assistance of pumps through openings like springs and artesian wells.
Due to the karst hydrogeology of the Edwards Aquifer, chemicals that enter the system have the potential to rapidly travel through the aquifer and contaminate down-gradient water sources in a short period of time (hours to days).Assessment, U. E. N. C. for E. Karst Hydrology and Chemical Contamination. at
Edwards Aquifer is home to a large number of invertebrate species, 40 of which have been described. The most diverse groups are the prosobranch gastropods and amphipod crustaceans. The Edwards Aquifer has the highest recorded diversity of in the world. In the United States, only the fauna of the Edwards Aquifer of Texas has a significant component of marine-derived species. Of the major karst regions in the United States, it is the only one with a significant marine component. Of the 64 stygobionts known from the Edwards Aquifer, 17 are marine relics. The U.S. Fish and Wildlife Service (USFWS) consider the Comal and San Marcos Springs ecosystems to have one of the greatest known diversities of organisms of any aquatic ecosystem in the Southwestern United States.San Marcos/Comal Recovery Team, U.S. Fish & Wildlife Service. (1996). San Marcos and Comal Springs and Associated Aquatic Ecosystems (Revised) Recovery Plan 6 This is due in part to the constant nature of the temperature and flow of the aquifer waters that have created unique ecosystems supporting a high degree of endemism.Wilson, E.O. (1992). The Diversity of Life 397. The Edwards Aquifer is the sole environment for the rare Barton Springs salamander ( Eurycea sosorum), which is a federally listed endangered species. At Comal and San Marcos Springs, their openings and in the rivers and lakes originating from the springs, one threatened and seven endangered species have been listed by USFWS under the Endangered Species Act of 1973. The San Marcos salamander ( Eurycea nana) is listed as threatened. The San Marcos gambusia ( Gambusia georgei), Texas wild rice ( Zizania texana), fountain darter ( Etheostoma fonticola), Texas blind salamander ( Eurycea rathbuni), Comal Springs riffle beetle ( Heterelmis comalensis), Comal Springs dryopid beetle ( Stygoparnus comalensis), and Peck's cave amphipod ( Stygobromus pecki) are listed as endangered. Another species, the Blanco blind salamander, is unlisted because it is unknown whether the species is extant or extinct.
Almost all of agricultural lands and a large portion of San Antonio overlie the confined portion of the aquifer (Barker 1996). In an effort to preserve undeveloped land the city of San Antonio passed the Edwards Aquifer Protection Plan in 2000 (renewed in 2005, 2010 and 2015). The plan allows the city to purchase conservation easements for land in Bexar, Medina and Uvalde counties. The landowners retain and upon agreement the landowners cannot divide or develop the land and are paid 40-45% of market value for the easement. The plan has over enrolled.
Between 1990 and 2015, the population increased by two thirds, at this rate, the population of the basin will be doubled in 2050. The population across the counties have approximately the same growth rate of 10% per year. However, Comal and Guadalupe have a greater growth rate of more than 25% per year. This will increase the number of people relying on the aquifer for daily water use.
All of these economic practices in the region put pressure on both the quantity and quality of water in the Edwards Aquifer. A recent study showed that salinity in groundwater wells in the aquifer is high, potentially affected by adjacent, natural salt deposits as well as brine seepage from nearby oil fields. Additionally, irrigated agriculture is a significant user of the Edwards Aquifer groundwater, with a variety of crops cultivated, including: " vegetables, hay sesame, soybeans, peanuts, cotton, corn, sorghum, wheat, and oats". Also, the city of San Antonio is located along the eastern edge of the aquifer and was listed as the 7th largest city in the United States by population in 2014.
In addition to the 2.3 million San Antonio residents are the communities of New Braunfels and San Marcos that depend on the aquifer for clean drinking water. Farming and ranching communities are other significant dependents of the aquifer. From the 1930s to the 1980s, withdrawals have quadrupled with over half of the current withdrawals serving municipal water purposes while the remaining goes to agricultural needs.Hamilton JM. 2003. Edwards Aquifer Authority Hydrogeologic Data Report for 2002. San Antonio (TX): Edwards Aquifer Authority.US Fish and Wildlife Service. 1995. San Marcos and Comal Springs and Associated Aquatic Ecosystems (Revised) Recovery Plan. Albuquerque (NM): USFWS. More than 50,000 people in the city of Austin (6% of Austin's population) rely on the Barton Springs segment of the Edwards Aquifer.
Five groups of stakeholders have played significant roles in shaping the use and conservation of the aquifer, including the Edwards Aquifer Authority (EAA), New Braunfels, San Marcos, San Antonio, and Texas State University."Water for All. Diverse stakeholders are lauded for work to conserve Edwards Aquifer." Texas Parks and Wildlife Magazine July 2014. Additionally, federal entities including US Geological Survey, US Fish and Wildlife Service, and US Environmental Protection Agency have been involved in water steward activities and recovery management plans of the Edwards aquifer system.
The EAA was created as a result of Edwards Aquifer Authority Act enacted by Texas State Legislature in 1993. The main purpose of EAA is to oversee the permitting system for water withdrawals from the aquifer system. A subdivision of state government, EAA is more of a liaison between federal agencies (e.g. USFWS, USEPA, USGS), state agencies (e.g. Texas Water Development Board, Texas Commission on Environmental Quality, etc.) and non-governmental organizations (e.g. Texas Water Conservation Association, Texas Association of Groundwater Districts).
| +Main stakeholders involved in water resources management in the Edwards aquifer system !Stakeholders !Involvement in aquifer resources management | |
| Farmers and ranchers | Depend on water for crops and animal husbandry |
| Edwards Aquifer Authority | Responsible for permitting process for water withdrawal from the Edwards aquifer system |
| Metropolitan areas: Uvalde, San Antonio, New Braunfels, and San Marcos | Depend on water for drinking, recreational uses, utilities, and for irrigation |
| San Antonio Water System (SAWS) | Largest public utility system that relies on Edwards aquifer system. |
In 1992, the TWQB declared the Edwards aquifer an underground river due to the presence of endangered species, but this was overturned later the same year. In 1993, Texas Senate Bill 1477 established the Edwards Aquifer Authority to manage the aquifer and to limit pumping to protect the spring flow levels.
In 1997, Chapter 36 of the Texas Water Code was amended by Senate Bill 1 of the 75th Texas Legislature to require all underground water conservation districts in Texas to develop a groundwater management plan and submit it for approval by the Texas Water Development Board every five years on the anniversary of initial approval (September 17, 1998 for the Edwards Aquifer Authority). The initial requirements of the groundwater management plans were that they address the efficient use of groundwater, methods of controlling and preventing waste of groundwater, conjunctive surface water issues, natural resource issues that affect the use and availability, of groundwater, and methods of controlling and preventing subsidence.
The requirements of groundwater management plans have since undergone expansion to require the inclusion of planning requirements for addressing drought conditions and conservation (2001, the 77th Texas Legislature Senate Bill 2), estimates of the managed available groundwater, the amount of groundwater used within each district, the amount of recharge from precipitation, projected surface water supply, total water demand within the district, and consideration of water management strategies that were included in the adopted state water plan (2005, 79th Texas Legislature HB 1763). Senate Bill 2 of the 77th Texas Legislature also required the groundwater conservation districts to submit groundwater management plans to the Chair of any Regional Water Planning Group in which any part of the district is located so that they may specify any area(s) that conflict with the approved Regional Water Plan1.
In addition to the groundwater management plan, the Edwards Aquifer Authority board of directors maintains a three-year rolling strategic plan that is updated annually. The 2015-2017 strategic plan adopted on October 14, 2014 identifies six major goals:
Annual storage can be negative during dry years with high water use and positive during wet years with relatively low water use. A long-term negative imbalance between recharge and discharge in an aquifer may lead to the depletion of the available water in the aquifer.
Annual storage between 1955 and 2012 estimated from data provided by a continuing program between the U.S. Geologic Survey and the Edwards Aquifer Authority ranged from . The average storage during this period was .
The Contributing Zone, which occurs on of the Edwards Plateau (Texas Hill Country), collects precipitation and streamflow that drain to the Recharge Zone. Major streams draining the Contributing Zone include Cibolo Creek, Helotes Creek, Barton Creek, and Onion Creek.Blome, Charles D., Jason R. Faith, Diana E. Pedraza, et al. (2005). USGS, US Department of Interior, and US Geological Survey.
Average precipitation in the region is around per year.Official Aquifer Level and Statistics (2015). San Antonio Water System. Retrieved 13 October 2015.
Annual well discharge—the sum of all well discharges in a year— ranged from between 1955 and 2012. The average well discharge for this period was approximately , equivalent to 183,000 Olympic-sized swimming pools.
Annual spring discharge ranged from between 1955 and 2012. The average spring discharge for this period was approximately .
During dry years, more water is discharged from wells while during wet years, more water is discharged from springs. Annual total groundwater discharge from pumping and springs ranged from , and the average total groundwater discharge for 1955 to 2012 period was approximately .
Aquifer storage is correlated with water levels recorded in the J-17 Bexar Monitoring wells which serves as the sole official monitoring well in the Edwards Aquifer. The J-17 well, is located in the artisanal confined Edwards Aquifer at a location AY-68-37-203 based on the latitude and longitude. Water levels have been recorded in the J-17 well since the 1910s, and is used to generalize the entire aquifer system. Changes in aquifer storage are used to estimate recharge rates.
In the Edwards aquifer, groundwater flow models have been developed for the San Antonio and Barton Springs aquifer segments in the San Antonio region of Texas. Two model simulations were conducted: steady state and transient. A steady-state groundwater flow model requires magnitude and direction of flow remain constant, whereas a transient model simulation allows for a change in water storage over time. Steady-state results suggest water leaving the aquifer occurs through springs (73.3 percent), water well pumping (25.7 percent), and to the Colorado River (0.6 percent). Inflow of water to the aquifer mostly occurs through natural recharge (93.5 percent) and water delivered through the aquifer's regional boundaries (6.5 percent). The transient simulation model also suggests discharge primarily occurs through springs, followed by water well pumping; however, changes in water storage is heavily dependent upon the amount of monthly precipitation and water well pumping volumes.Lindgren, R., Dutton, A., Hovorka, S., Worthington, S. Painter, S. 2004. Conceptualization and Simulation of the Edwards Aquifer, San Antonio Region Texas. United States Geological Survey Scientific Investigations Report 2004-5277, 154 p.
Wells that produce less than 25,000 gallons per day, wells that are solely for the purpose of watering livestock, and a few other exceptions are considered exempt wells that do not require a permit. Permits for withdrawal can be transferred to another user, provided that the new use is beneficial and occurs within the boundaries of the Authority, with a few geographical exceptions.
Groundwater conservation plans are required for permit holders who withdraw more than , unless irrigators can prove more than 60 percent efficiency in their water use. Conservation plans require the use of Best Management Practices, as determined by the Edwards Aquifer Authority."Rules and Statutes." Edwards Aquifer Authority. N.p., n.d. Web. 9 Oct. 2015.
In recharge zones of the aquifer permits are required to store regulated substances that could damage water quality. Additionally, The Texas Commission of Environmental Quality requires special permits for construction in the recharge zones of the aquifer.
The Texas Legislature directed the EAA to regulate pumping from the aquifer, implement critical period management restrictions, and pursue measures to ensure minimum continuous spring flows of the Comal and San Marcos Springs are maintained to protect endangered and threatened species to the extent required by federal law. In 2013, the U.S. Fish and Wildlife Service approved Edwards Aquifer Authority's Habitat Conservation Plan (HCP), which is a regional 15-year plan designed to protect the water flow and species in the Edwards Aquifer region.
The HCP supports three major project groups of habitat protection measures, flow protection measures, and supporting measures such as applied research, ecological and biological, and water-quality monitoring. HCP project examples include minimization and mitigation of the impacts of low flow, by restoring native riparian zones in order to benefit the Comal Springs riffle beetle by increasing the amount functional habitat and food sources (i.e., root structures and associated biofilms)."Habitat Protection Measures." EAHCP — Restoration of Riparian Zones and Riffle BeetleRiparian Improvement. N.p., n.d. Web. 23 Oct. 2015 http://www.eahcp.org/index.php/habitat_protection/comal_springs/restoration_of_riparian_zones_and_riffle_beetle_riparian_improvement The method of riparian zone establishment will include the removal of non-native, followed by the replanting of native vegetation that may be considered representative of a healthy, functioning riparian zone.
Although implementation of the HCP exists primarily within the EAA, a broad group of stakeholders plays a role in the management of the Edwards Aquifer. The National Research Council (NRC) committee, formed by the National Academy of Sciences (NAS), released the first of three scientific reports in 2015 that evaluate and make recommendations for Habitat Conservation Plan programming of the Edwards Aquifer.
In the initial lawsuit was Sierra Club v. Babbitt in 1991. The plaintiffs included environmental groups (Sierra Club), water districts (Guadalupe-Blanco River Authority and Bexar Metropolitan Water District), municipalities (City of San Marcos and City of New Braunfels), and utilities (Green Valley and Atascosa Rural Water Supply corporations). The defendants included, government agencies (US Fish and Wildlife Service, State of Texas, Texas Parks and Wildlife Department), City of San Antonio, and multiple industrial water users.
In Sierra Club v. Babbitt the plaintiffs claimed that the defendants were not fulfilling their duties under the Endangered Species Act, to protect endangered species and their ecosystems. The endangered species included the Fountain Darter, San Marcos Salamander, San Marcos Gambusia, Texas Blind Salamander, and Zizania texana. The ecosystems for these species depends on water from Comal Springs and San Marcos Springs which have the potential to run dry if too much water is withdrawn from Edwards Aquifer.
The final decision sided with the Sierra Club and other plaintiffs and in 1993 restrictions were placed on pumping from Edwards Aquifer. As an outcome of Sierra Club v. Babbitt as a result of this lawsuit, legislation was passed which created the Edwards Aquifer Authority. (2025). 9780309368872, National Academies Press. ISBN 9780309368872 This was also not the end of litigation, there was an attempt to appeal the initial Sierra Club v. Babbitt in 1993 Sierra Club v. Babbitt the appeal was denied because the US Fish and Wildlife Service agreed with the original ruling, and the City of San Antonio and industrial water users were unable to prove that they were injured by the original Sierra Club v. Babbitt ruling.
Due to Sierra Club v. Babbitt the Edwards Aquifer Act 1993 was passed which created the Edwards Aquifer Authority to oversee pumping regulations.Tex. Gen. Laws § 2350, ch. 626, 73rd. Leg. (1993). http://www.edwardsaquifer.org/files/download/5a48e1d88ffe061 In the case Barshop v. Medina Under. Wat. Cons. Dist. 1996, Medina County Under Water Conservation District challenged the Edwards Aquifer Authority over the constitutionality of the Edwards Aquifer Act. The challenge was over whether property owners have the constitutional right to pump water from their land, or whether concerns for water conservation and endangered species take precedence. Barshop v. Medina Under. Wat. Cons. Dist. went to the Texas Supreme Court where the Edwards Aquifer Act was upheld.
In an effort to reduce San Antonio's dependency on the solitary supply of the Edward's Aquifer, the San Antonio Water System (SAWS) has proposed a water supply pipeline, the Vista Ridge, extending 82,000 ft from Burleson County to San Antonio. SAWS reports that the Vista Ridge pipeline, running 54" in diameter, will supply as much as 50,000 ac-ft of water per year for 30 years, upon the project's estimated completion in 2019. This will increase the city's current water supply by 20%.
By 2020, SAWS estimates the average San Antonio residential water bill to be $88/mnth; this would place San Antonio at the lowest rate for water in any major Texan city. The water is provided through over 3,400 leases with private landowners drawing from the Caririzo and Simsboro aquifers. In an effort to protect the ratepayer (i.e. San Antonio citizens), the project proposes an undetermined lifeline rate. Any water that fails to be delivered (i.e. shortages, contamination) will be compensated by Blue Water Systems, L.P and not at the expense of the ratepayer.
This project is projected to promote job growth and prosperity surrounding the city, as the supply will withstand San Antonio's projected growth rate of 20,000 people/year. Companies invested in the project lobbied for a state drought-planning bill to enable regional approval for the sale of private activity bonds. Despite strong support from the house, the bill failed at the end of May 2015, due to lack of support in the senate. Consequently, the project requires approval from each of the seven counties along the route.
Those in favor of the Vista Ridge pipeline believe the project will help protect and sustain the Edwards Aquifer, as well as enable the conservation of diversified water. Those who oppose the pipeline are concerned that installment will damage the natural system's ability to recharge the Edwards Aquifer and retain soil moisture. Further, whether or not the city needs additional supply is in question, as projected increase in water demand is speculated to present commercial expansion, not San Antonio's municipal population demand. Environmental groups, such as the Sierra Club, suggest the project is allocating funds to an unsustainable solution, and that San Antonio should instead be "investing in alternative and innovative resources that are less expensive, less energy-intensive, and locally accessible."
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